Add signature

Fixes #176.

22 files changed, 544 insertions, 289 deletions

diff --git a/library/src/main/java/com/bumptech/glide/BitmapRequestBuilder.java b/library/src/main/java/com/bumptech/glide/BitmapRequestBuilder.java
index ce465ea1..6dc00262 100644
--- a/library/src/main/java/com/bumptech/glide/BitmapRequestBuilder.java
+++ b/library/src/main/java/com/bumptech/glide/BitmapRequestBuilder.java
@@ -1,14 +1,13 @@
 package com.bumptech.glide;
 
-import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.drawable.Drawable;
 import android.os.ParcelFileDescriptor;
 import android.view.animation.Animation;
 import android.widget.ImageView;
-
 import com.bumptech.glide.load.DecodeFormat;
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
@@ -22,8 +21,6 @@ import com.bumptech.glide.load.resource.bitmap.ImageVideoBitmapDecoder;
 import com.bumptech.glide.load.resource.bitmap.StreamBitmapDecoder;
 import com.bumptech.glide.load.resource.bitmap.VideoBitmapDecoder;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
-import com.bumptech.glide.manager.Lifecycle;
-import com.bumptech.glide.manager.RequestTracker;
 import com.bumptech.glide.provider.LoadProvider;
 import com.bumptech.glide.request.RequestListener;
 import com.bumptech.glide.request.animation.ViewPropertyAnimation;
@@ -47,18 +44,15 @@ import java.io.InputStream;
 public class BitmapRequestBuilder<ModelType, TranscodeType>
         extends GenericRequestBuilder<ModelType, ImageVideoWrapper, Bitmap, TranscodeType> implements BitmapOptions {
     private final BitmapPool bitmapPool;
-    private final Glide glide;
     private Downsampler downsampler = Downsampler.AT_LEAST;
     private DecodeFormat decodeFormat = DecodeFormat.PREFER_RGB_565;
     private ResourceDecoder<InputStream, Bitmap> imageDecoder;
     private ResourceDecoder<ParcelFileDescriptor, Bitmap> videoDecoder;
 
-    BitmapRequestBuilder(Context context, ModelType model,
-            LoadProvider<ModelType, ImageVideoWrapper, Bitmap, TranscodeType> streamLoadProvider,
-            Class<TranscodeType> transcodeClass, Glide glide, RequestTracker requestTracker, Lifecycle lifecycle) {
-        super(context, model, streamLoadProvider, transcodeClass, glide, requestTracker, lifecycle);
-        this.glide = glide;
-        this.bitmapPool = glide.getBitmapPool();
+    BitmapRequestBuilder(LoadProvider<ModelType, ImageVideoWrapper, Bitmap, TranscodeType> loadProvider,
+            Class<TranscodeType> transcodeClass, GenericRequestBuilder<ModelType, ?, ?, ?> other) {
+        super(loadProvider, transcodeClass, other);
+        this.bitmapPool = other.glide.getBitmapPool();
 
         imageDecoder = new StreamBitmapDecoder(bitmapPool);
         videoDecoder = new FileDescriptorBitmapDecoder(bitmapPool);
@@ -450,6 +444,12 @@ public class BitmapRequestBuilder<ModelType, TranscodeType>
         return this;
     }
 
+    @Override
+    public BitmapRequestBuilder<ModelType, TranscodeType> signature(Key signature) {
+        super.signature(signature);
+        return this;
+    }
+
     /**
      * {@inheritDoc}
      *
diff --git a/library/src/main/java/com/bumptech/glide/BitmapTypeRequest.java b/library/src/main/java/com/bumptech/glide/BitmapTypeRequest.java
index 8e99ef7e..2812e5d6 100644
--- a/library/src/main/java/com/bumptech/glide/BitmapTypeRequest.java
+++ b/library/src/main/java/com/bumptech/glide/BitmapTypeRequest.java
@@ -1,16 +1,12 @@
 package com.bumptech.glide;
 
-import android.content.Context;
 import android.graphics.Bitmap;
 import android.os.ParcelFileDescriptor;
-
 import com.bumptech.glide.load.model.ImageVideoModelLoader;
 import com.bumptech.glide.load.model.ImageVideoWrapper;
 import com.bumptech.glide.load.model.ModelLoader;
 import com.bumptech.glide.load.resource.transcode.BitmapBytesTranscoder;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
-import com.bumptech.glide.manager.Lifecycle;
-import com.bumptech.glide.manager.RequestTracker;
 import com.bumptech.glide.provider.DataLoadProvider;
 import com.bumptech.glide.provider.FixedLoadProvider;
 
@@ -24,14 +20,11 @@ import java.io.InputStream;
  * @param <ModelType> The type of model to load the {@link Bitmap} or transcoded class from.
  */
 public class BitmapTypeRequest<ModelType> extends BitmapRequestBuilder<ModelType, Bitmap> {
-    private final Context context;
     private final ModelType model;
     private final ModelLoader<ModelType, InputStream> streamModelLoader;
     private final ModelLoader<ModelType, ParcelFileDescriptor> fileDescriptorModelLoader;
     private final Glide glide;
-    private final RequestTracker requestTracker;
     private final RequestManager.OptionsApplier optionsApplier;
-    private final Lifecycle lifecycle;
 
     private static <A, R> FixedLoadProvider<A, ImageVideoWrapper, Bitmap, R> buildProvider(Glide glide,
             ModelLoader<A, InputStream> streamModelLoader,
@@ -52,22 +45,16 @@ public class BitmapTypeRequest<ModelType> extends BitmapRequestBuilder<ModelType
         return new FixedLoadProvider<A, ImageVideoWrapper, Bitmap, R>(modelLoader, transcoder, loadProvider);
     }
 
-    BitmapTypeRequest(Context context, ModelType model,
+    BitmapTypeRequest(GenericRequestBuilder<ModelType, ?, ?, ?> other,
             ModelLoader<ModelType, InputStream> streamModelLoader,
             ModelLoader<ModelType, ParcelFileDescriptor> fileDescriptorModelLoader,
-            Glide glide, RequestTracker requestTracker, Lifecycle lifecycle,
             RequestManager.OptionsApplier optionsApplier) {
-        super(context, model,
-                buildProvider(glide, streamModelLoader, fileDescriptorModelLoader, Bitmap.class, null),
-                Bitmap.class,
-                glide, requestTracker, lifecycle);
-        this.context = context;
-        this.model = model;
+        super(buildProvider(other.glide, streamModelLoader, fileDescriptorModelLoader, Bitmap.class, null),
+                Bitmap.class, other);
         this.streamModelLoader = streamModelLoader;
         this.fileDescriptorModelLoader = fileDescriptorModelLoader;
-        this.glide = glide;
-        this.requestTracker = requestTracker;
-        this.lifecycle = lifecycle;
+        this.model = other.model;
+        this.glide = other.glide;
         this.optionsApplier = optionsApplier;
     }
 
@@ -81,9 +68,9 @@ public class BitmapTypeRequest<ModelType> extends BitmapRequestBuilder<ModelType
      */
     public <R> BitmapRequestBuilder<ModelType, R> transcode(ResourceTranscoder<Bitmap, R> transcoder,
             Class<R> transcodeClass) {
-        return optionsApplier.apply(model, new BitmapRequestBuilder<ModelType, R>(context, model,
+        return optionsApplier.apply(model, new BitmapRequestBuilder<ModelType, R>(
                 buildProvider(glide, streamModelLoader, fileDescriptorModelLoader, transcodeClass, transcoder),
-                transcodeClass, glide, requestTracker, lifecycle));
+                transcodeClass, this));
     }
 
     /**
diff --git a/library/src/main/java/com/bumptech/glide/DrawableRequestBuilder.java b/library/src/main/java/com/bumptech/glide/DrawableRequestBuilder.java
index 7dde002d..ce01593a 100644
--- a/library/src/main/java/com/bumptech/glide/DrawableRequestBuilder.java
+++ b/library/src/main/java/com/bumptech/glide/DrawableRequestBuilder.java
@@ -5,8 +5,8 @@ import android.graphics.Bitmap;
 import android.graphics.drawable.Drawable;
 import android.view.animation.Animation;
 import android.widget.ImageView;
-
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
@@ -40,16 +40,11 @@ import java.io.File;
 public class DrawableRequestBuilder<ModelType>
         extends GenericRequestBuilder<ModelType, ImageVideoWrapper, GifBitmapWrapper, GlideDrawable>
         implements BitmapOptions, DrawableOptions {
-    private final Glide glide;
-    private final Context context;
 
     DrawableRequestBuilder(Context context, ModelType model,
             LoadProvider<ModelType, ImageVideoWrapper, GifBitmapWrapper, GlideDrawable> loadProvider, Glide glide,
             RequestTracker requestTracker, Lifecycle lifecycle) {
         super(context, model, loadProvider, GlideDrawable.class, glide, requestTracker, lifecycle);
-        this.context = context;
-        this.glide = glide;
-
         // Default to animating.
         crossFade();
     }
@@ -402,6 +397,12 @@ public class DrawableRequestBuilder<ModelType>
         return this;
     }
 
+    @Override
+    public DrawableRequestBuilder<ModelType> signature(Key signature) {
+        super.signature(signature);
+        return this;
+    }
+
     /**
      * {@inheritDoc}
      *
diff --git a/library/src/main/java/com/bumptech/glide/DrawableTypeRequest.java b/library/src/main/java/com/bumptech/glide/DrawableTypeRequest.java
index 84520056..21c1139f 100644
--- a/library/src/main/java/com/bumptech/glide/DrawableTypeRequest.java
+++ b/library/src/main/java/com/bumptech/glide/DrawableTypeRequest.java
@@ -2,7 +2,6 @@ package com.bumptech.glide;
 
 import android.content.Context;
 import android.os.ParcelFileDescriptor;
-
 import com.bumptech.glide.load.model.ImageVideoModelLoader;
 import com.bumptech.glide.load.model.ImageVideoWrapper;
 import com.bumptech.glide.load.model.ModelLoader;
@@ -30,12 +29,7 @@ import java.io.InputStream;
 public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<ModelType> implements DownloadOptions {
     private final ModelLoader<ModelType, InputStream> streamModelLoader;
     private final ModelLoader<ModelType, ParcelFileDescriptor> fileDescriptorModelLoader;
-    private final Context context;
-    private final Glide glide;
-    private final RequestTracker requestTracker;
     private final RequestManager.OptionsApplier optionsApplier;
-    private final Lifecycle lifecycle;
-    private final ModelType model;
 
     private static <A, Z, R> FixedLoadProvider<A, ImageVideoWrapper, Z, R> buildProvider(Glide glide,
             ModelLoader<A, InputStream> streamModelLoader,
@@ -63,14 +57,9 @@ public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<Model
                 buildProvider(glide, streamModelLoader, fileDescriptorModelLoader, GifBitmapWrapper.class,
                         GlideDrawable.class, null),
                 glide, requestTracker, lifecycle);
-        this.model = model;
         this.streamModelLoader = streamModelLoader;
         this.fileDescriptorModelLoader = fileDescriptorModelLoader;
-        this.context = context;
-        this.glide = glide;
-        this.requestTracker = requestTracker;
         this.optionsApplier = optionsApplier;
-        this.lifecycle = lifecycle;
     }
 
     /**
@@ -79,8 +68,8 @@ public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<Model
      * @return A new request builder for loading a {@link android.graphics.Bitmap}
      */
     public BitmapTypeRequest<ModelType> asBitmap() {
-        return optionsApplier.apply(model, new BitmapTypeRequest<ModelType>(context, model, streamModelLoader,
-                fileDescriptorModelLoader, glide, requestTracker, lifecycle, optionsApplier));
+        return optionsApplier.apply(model, new BitmapTypeRequest<ModelType>(this, streamModelLoader,
+                fileDescriptorModelLoader, optionsApplier));
     }
 
     /**
@@ -96,8 +85,7 @@ public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<Model
      * @return A new request builder for loading a {@link com.bumptech.glide.load.resource.gif.GifDrawable}.
      */
     public GifTypeRequest<ModelType> asGif() {
-        return optionsApplier.apply(model, new GifTypeRequest<ModelType>(context, model, streamModelLoader, glide,
-                requestTracker, lifecycle, optionsApplier));
+        return optionsApplier.apply(model, new GifTypeRequest<ModelType>(this, streamModelLoader, optionsApplier));
     }
 
     /**
@@ -115,7 +103,7 @@ public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<Model
     }
 
     private GenericTranscodeRequest<ModelType, InputStream, File> getDownloadOnlyRequest() {
-        return optionsApplier.apply(model, new GenericTranscodeRequest<ModelType, InputStream, File>(context, glide,
-                model, streamModelLoader, InputStream.class, File.class, requestTracker, lifecycle, optionsApplier));
+        return optionsApplier.apply(model, new GenericTranscodeRequest<ModelType, InputStream, File>(File.class, this,
+                streamModelLoader, InputStream.class, File.class, optionsApplier));
     }
 }
diff --git a/library/src/main/java/com/bumptech/glide/GenericRequestBuilder.java b/library/src/main/java/com/bumptech/glide/GenericRequestBuilder.java
index b56c327b..1d3fc690 100644
--- a/library/src/main/java/com/bumptech/glide/GenericRequestBuilder.java
+++ b/library/src/main/java/com/bumptech/glide/GenericRequestBuilder.java
@@ -4,8 +4,9 @@ import android.content.Context;
 import android.graphics.drawable.Drawable;
 import android.view.animation.Animation;
 import android.widget.ImageView;
-
+import com.bumptech.glide.signature.EmptySignature;
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.MultiTransformation;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
@@ -49,13 +50,15 @@ import java.io.File;
  * @param <TranscodeType> The type of resource the decoded resource will be transcoded to.
  */
 public class GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> {
-    private final Context context;
-    private final ModelType model;
+    protected final Context context;
+    protected final Glide glide;
+    protected final ModelType model;
+    protected final Class<TranscodeType> transcodeClass;
+    protected final RequestTracker requestTracker;
+    protected final Lifecycle lifecycle;
     private final ChildLoadProvider<ModelType, DataType, ResourceType, TranscodeType> loadProvider;
-    private final Class<TranscodeType> transcodeClass;
-    private final Glide glide;
-    private final RequestTracker requestTracker;
-    private final Lifecycle lifecycle;
+
+    private Key signature = EmptySignature.obtain();
 
     private int placeholderId;
     private int errorId;
@@ -74,9 +77,18 @@ public class GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeT
     private Transformation<ResourceType> transformation = UnitTransformation.get();
     private boolean isTransformationSet;
 
+    GenericRequestBuilder(LoadProvider<ModelType, DataType, ResourceType, TranscodeType> loadProvider,
+            Class<TranscodeType> transcodeClass, GenericRequestBuilder<ModelType, ?, ?, ?> other) {
+        this(other.context, other.model, loadProvider, transcodeClass, other.glide, other.requestTracker,
+                other.lifecycle);
+        this.signature = other.signature;
+    }
+
     GenericRequestBuilder(Context context, ModelType model,
             LoadProvider<ModelType, DataType, ResourceType, TranscodeType> loadProvider,
             Class<TranscodeType> transcodeClass, Glide glide, RequestTracker requestTracker, Lifecycle lifecycle) {
+        this.context = context;
+        this.model = model;
         this.transcodeClass = transcodeClass;
         this.glide = glide;
         this.requestTracker = requestTracker;
@@ -90,8 +102,6 @@ public class GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeT
         if (model != null && loadProvider == null) {
             throw new NullPointerException("LoadProvider must not be null");
         }
-        this.context = context;
-        this.model = model;
     }
 
     /**
@@ -505,6 +515,28 @@ public class GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeT
     }
 
     /**
+     * Sets some additional data to be mixed in to the memory and disk cache keys allowing the caller more control over
+     * when cached data is invalidated.
+     *
+     * <p>
+     *     Note - The signature does not replace the cache key, it is purely additive.
+     * </p>
+     *
+     * @see com.bumptech.glide.signature.StringSignature
+     *
+     * @param signature A unique non-null {@link com.bumptech.glide.load.Key} representing the current state of the
+     *                  model that will be mixed in to the cache key.
+     * @return This request builder.
+     */
+    public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> signature(Key signature) {
+        if (signature == null) {
+            throw new NullPointerException("Signature must not be null");
+        }
+        this.signature = signature;
+        return this;
+    }
+
+    /**
      * Set the target the resource will be loaded into.
      *
      * @see Glide#clear(com.bumptech.glide.request.target.Target)
@@ -676,6 +708,7 @@ public class GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeT
         return GenericRequest.obtain(
                 loadProvider,
                 model,
+                signature,
                 context,
                 priority,
                 target,
diff --git a/library/src/main/java/com/bumptech/glide/GenericTranscodeRequest.java b/library/src/main/java/com/bumptech/glide/GenericTranscodeRequest.java
index 9960c06c..4274cb6e 100644
--- a/library/src/main/java/com/bumptech/glide/GenericTranscodeRequest.java
+++ b/library/src/main/java/com/bumptech/glide/GenericTranscodeRequest.java
@@ -1,7 +1,6 @@
 package com.bumptech.glide;
 
 import android.content.Context;
-
 import com.bumptech.glide.load.engine.DiskCacheStrategy;
 import com.bumptech.glide.load.model.ModelLoader;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
@@ -31,15 +30,10 @@ import java.io.File;
  */
 public class GenericTranscodeRequest<ModelType, DataType, ResourceType>
         extends GenericRequestBuilder<ModelType, DataType, ResourceType, ResourceType> implements DownloadOptions {
-    private final Context context;
-    private final ModelType model;
-    private final Glide glide;
     private final ModelLoader<ModelType, DataType> modelLoader;
     private final Class<DataType> dataClass;
     private final Class<ResourceType> resourceClass;
-    private final RequestTracker requestTracker;
     private final RequestManager.OptionsApplier optionsApplier;
-    private final Lifecycle lifecycle;
 
     private static <A, T, Z, R> LoadProvider<A, T, Z, R> build(Glide glide, ModelLoader<A, T> modelLoader,
             Class<T> dataClass, Class<Z> resourceClass, ResourceTranscoder<Z, R> transcoder) {
@@ -47,21 +41,27 @@ public class GenericTranscodeRequest<ModelType, DataType, ResourceType>
         return new FixedLoadProvider<A, T, Z, R>(modelLoader, transcoder, dataLoadProvider);
     }
 
+    GenericTranscodeRequest(
+            Class<ResourceType> transcodeClass, GenericRequestBuilder<ModelType, ?, ?, ?> other,
+            ModelLoader<ModelType, DataType> modelLoader, Class<DataType> dataClass, Class<ResourceType> resourceClass,
+            RequestManager.OptionsApplier optionsApplier) {
+        super(build(other.glide, modelLoader, dataClass, resourceClass, UnitTranscoder.<ResourceType>get()),
+                transcodeClass, other);
+        this.modelLoader = modelLoader;
+        this.dataClass = dataClass;
+        this.resourceClass = resourceClass;
+        this.optionsApplier = optionsApplier;
+    }
+
     GenericTranscodeRequest(Context context, Glide glide, ModelType model, ModelLoader<ModelType, DataType> modelLoader,
             Class<DataType> dataClass, Class<ResourceType> resourceClass, RequestTracker requestTracker,
             Lifecycle lifecycle, RequestManager.OptionsApplier optionsApplier) {
-        super(context, model,
-                build(glide, modelLoader, dataClass, resourceClass, UnitTranscoder.<ResourceType>get()),
+        super(context, model, build(glide, modelLoader, dataClass, resourceClass, UnitTranscoder.<ResourceType>get()),
                 resourceClass, glide, requestTracker, lifecycle);
-        this.context = context;
-        this.model = model;
-        this.glide = glide;
         this.modelLoader = modelLoader;
         this.dataClass = dataClass;
         this.resourceClass = resourceClass;
-        this.requestTracker = requestTracker;
         this.optionsApplier = optionsApplier;
-        this.lifecycle = lifecycle;
     }
 
     /**
@@ -78,8 +78,8 @@ public class GenericTranscodeRequest<ModelType, DataType, ResourceType>
                 dataClass, resourceClass, transcoder);
 
         return optionsApplier.apply(model,
-                new GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType>(context, model,
-                loadProvider, transcodeClass, glide, requestTracker, lifecycle));
+                new GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType>(loadProvider,
+                        transcodeClass, this));
     }
 
     /**
@@ -101,13 +101,10 @@ public class GenericTranscodeRequest<ModelType, DataType, ResourceType>
         DataLoadProvider<DataType, File> dataLoadProvider = glide.buildDataProvider(dataClass, File.class);
         FixedLoadProvider<ModelType, DataType, File, File> fixedLoadProvider =
                 new FixedLoadProvider<ModelType, DataType, File, File>(modelLoader, transcoder, dataLoadProvider);
-        return optionsApplier.apply(model, new GenericRequestBuilder<ModelType, DataType, File, File>(context, model,
-                fixedLoadProvider,
-                File.class, glide,
-                requestTracker, lifecycle)
+        return optionsApplier.apply(model, new GenericRequestBuilder<ModelType, DataType, File, File>(fixedLoadProvider,
+                File.class, this))
                 .priority(Priority.LOW)
                 .diskCacheStrategy(DiskCacheStrategy.SOURCE)
-                .skipMemoryCache(true));
-
+                .skipMemoryCache(true);
     }
 }
diff --git a/library/src/main/java/com/bumptech/glide/GifRequestBuilder.java b/library/src/main/java/com/bumptech/glide/GifRequestBuilder.java
index 1059b7ca..d6918f68 100644
--- a/library/src/main/java/com/bumptech/glide/GifRequestBuilder.java
+++ b/library/src/main/java/com/bumptech/glide/GifRequestBuilder.java
@@ -1,11 +1,10 @@
 package com.bumptech.glide;
 
-import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.drawable.Drawable;
 import android.view.animation.Animation;
-
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
@@ -14,8 +13,6 @@ import com.bumptech.glide.load.resource.bitmap.BitmapTransformation;
 import com.bumptech.glide.load.resource.gif.GifDrawable;
 import com.bumptech.glide.load.resource.gif.GifDrawableTransformation;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
-import com.bumptech.glide.manager.Lifecycle;
-import com.bumptech.glide.manager.RequestTracker;
 import com.bumptech.glide.provider.LoadProvider;
 import com.bumptech.glide.request.RequestListener;
 import com.bumptech.glide.request.animation.DrawableCrossFadeViewAnimation;
@@ -37,15 +34,10 @@ import java.io.InputStream;
 public class GifRequestBuilder<ModelType>
         extends GenericRequestBuilder<ModelType, InputStream, GifDrawable, GifDrawable>
         implements BitmapOptions, DrawableOptions {
-    private final Context context;
-    private final Glide glide;
 
-    GifRequestBuilder(Context context, ModelType model,
-            LoadProvider<ModelType, InputStream, GifDrawable, GifDrawable> loadProvider, Glide glide,
-            RequestTracker requestTracker, Lifecycle lifecycle) {
-        super(context, model, loadProvider, GifDrawable.class, glide, requestTracker, lifecycle);
-        this.context = context;
-        this.glide = glide;
+    GifRequestBuilder(LoadProvider<ModelType, InputStream, GifDrawable, GifDrawable> loadProvider,
+            Class<GifDrawable> transcodeClass, GenericRequestBuilder<ModelType, ?, ?, ?> other) {
+        super(loadProvider, transcodeClass, other);
     }
 
     /**
@@ -397,6 +389,12 @@ public class GifRequestBuilder<ModelType>
     }
 
     @Override
+    public GifRequestBuilder<ModelType> signature(Key signature) {
+        super.signature(signature);
+        return this;
+    }
+
+    @Override
     void applyFitCenter() {
         fitCenter();
     }
diff --git a/library/src/main/java/com/bumptech/glide/GifTypeRequest.java b/library/src/main/java/com/bumptech/glide/GifTypeRequest.java
index 857e516f..bded0f99 100644
--- a/library/src/main/java/com/bumptech/glide/GifTypeRequest.java
+++ b/library/src/main/java/com/bumptech/glide/GifTypeRequest.java
@@ -1,13 +1,9 @@
 package com.bumptech.glide;
 
-import android.content.Context;
-
 import com.bumptech.glide.load.model.ModelLoader;
 import com.bumptech.glide.load.resource.gif.GifDrawable;
 import com.bumptech.glide.load.resource.transcode.GifDrawableBytesTranscoder;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
-import com.bumptech.glide.manager.Lifecycle;
-import com.bumptech.glide.manager.RequestTracker;
 import com.bumptech.glide.provider.DataLoadProvider;
 import com.bumptech.glide.provider.FixedLoadProvider;
 
@@ -22,13 +18,8 @@ import java.io.InputStream;
  *           transcoded class from.
  */
 public class GifTypeRequest<ModelType> extends GifRequestBuilder<ModelType> {
-    private final Context context;
-    private final ModelType model;
     private final ModelLoader<ModelType, InputStream> streamModelLoader;
-    private final Glide glide;
-    private final RequestTracker requestTracker;
     private final RequestManager.OptionsApplier optionsApplier;
-    private final Lifecycle lifecycle;
 
     private static <A, R> FixedLoadProvider<A, InputStream, GifDrawable, R> buildProvider(Glide glide,
             ModelLoader<A, InputStream> streamModelLoader, Class<R> transcodeClass,
@@ -45,17 +36,11 @@ public class GifTypeRequest<ModelType> extends GifRequestBuilder<ModelType> {
         return new FixedLoadProvider<A, InputStream, GifDrawable, R>(streamModelLoader, transcoder, dataLoadProvider);
     }
 
-    GifTypeRequest(Context context, ModelType model, ModelLoader<ModelType, InputStream> streamModelLoader, Glide glide,
-            RequestTracker requestTracker, Lifecycle lifecycle, RequestManager.OptionsApplier optionsApplier) {
-        super(context, model, buildProvider(glide, streamModelLoader, GifDrawable.class, null),  glide,
-                requestTracker, lifecycle);
-        this.context = context;
-        this.model = model;
+    GifTypeRequest(GenericRequestBuilder<ModelType, ?, ?, ?> other,
+            ModelLoader<ModelType, InputStream> streamModelLoader, RequestManager.OptionsApplier optionsApplier) {
+        super(buildProvider(other.glide, streamModelLoader, GifDrawable.class, null), GifDrawable.class, other);
         this.streamModelLoader = streamModelLoader;
-        this.glide = glide;
-        this.requestTracker = requestTracker;
         this.optionsApplier = optionsApplier;
-        this.lifecycle = lifecycle;
 
         // Default to animating.
         crossFade();
@@ -77,8 +62,8 @@ public class GifTypeRequest<ModelType> extends GifRequestBuilder<ModelType> {
             ResourceTranscoder<GifDrawable, R> transcoder, Class<R> transcodeClass) {
         FixedLoadProvider<ModelType, InputStream, GifDrawable, R> provider = buildProvider(glide, streamModelLoader,
                 transcodeClass, transcoder);
-        return optionsApplier.apply(model, new GenericRequestBuilder<ModelType, InputStream, GifDrawable, R>(context,
-                model, provider, transcodeClass, glide, requestTracker, lifecycle));
+        return optionsApplier.apply(model,
+                new GenericRequestBuilder<ModelType, InputStream, GifDrawable, R>(provider, transcodeClass, this));
     }
 
     /**
diff --git a/library/src/main/java/com/bumptech/glide/RequestManager.java b/library/src/main/java/com/bumptech/glide/RequestManager.java
index 3e2b751b..3b6ba991 100644
--- a/library/src/main/java/com/bumptech/glide/RequestManager.java
+++ b/library/src/main/java/com/bumptech/glide/RequestManager.java
@@ -5,7 +5,6 @@ import android.net.Uri;
 import android.os.Handler;
 import android.os.Looper;
 import android.os.ParcelFileDescriptor;
-
 import com.bumptech.glide.load.model.ModelLoader;
 import com.bumptech.glide.load.model.file_descriptor.FileDescriptorModelLoader;
 import com.bumptech.glide.load.model.stream.MediaStoreStreamLoader;
@@ -36,7 +35,7 @@ import java.util.UUID;
  */
 public class RequestManager implements LifecycleListener {
     private final Context context;
-    private Lifecycle lifecycle;
+    private final Lifecycle lifecycle;
     private final RequestTracker requestTracker;
     private final Glide glide;
     private final OptionsApplier optionsApplier;
@@ -167,98 +166,111 @@ public class RequestManager implements LifecycleListener {
     }
 
     /**
-     * Use the given generic model loader to load the given generic data class.
+     * Returns a request builder that uses the given {@link com.bumptech.glide.load.model.ModelLoader} to fetch a
+     * generic data type.
+     *
      * <p>
      *     Warning - This is an experimental api that may change without a change in major version.
      * </p>
+     *
      * @param modelLoader The {@link ModelLoader} class to use to load the model.
      * @param dataClass The type of data the {@link ModelLoader} will load.
      * @param <A> The type of the model to be loaded.
      * @param <T> The type of the data to be loaded from the mode.
-     * @return A {@link GenericModelRequest} to set options for the load and ultimately the target to load the model
-     * into.
      */
     public <A, T> GenericModelRequest<A, T> using(ModelLoader<A, T> modelLoader, Class<T> dataClass) {
         return new GenericModelRequest<A, T>(modelLoader, dataClass);
     }
 
     /**
-     * Set the {@link ModelLoader} to use for for a new load where the model loader translates from a model to an
-     * {@link InputStream} resource for loading images.
+     * Returns a request builder that uses the given {@link com.bumptech.glide.load.model.stream.StreamModelLoader} to
+     * fetch an {@link InputStream} for loading images.
      *
      * @param modelLoader The model loader to use.
      * @param <T> The type of the model.
-     * @return A new {@link ImageModelRequest}.
      */
     public <T> ImageModelRequest<T> using(final StreamModelLoader<T> modelLoader) {
         return new ImageModelRequest<T>(modelLoader);
     }
 
     /**
-     * A convenience method to use a {@link StreamByteArrayLoader} to decode an image from a byte array.
+     * Returns a request builder that uses the given
+     * {@link com.bumptech.glide.load.model.stream.StreamByteArrayLoader} to fetch an {@link java.io.InputStream} for
+     * loading Bitmaps.
      *
      * @param modelLoader The byte array loader.
-     * @return A new {@link ImageModelRequest}.
      */
     public ImageModelRequest<byte[]> using(StreamByteArrayLoader modelLoader) {
         return new ImageModelRequest<byte[]>(modelLoader);
     }
 
     /**
-     * Set the {@link ModelLoader} to use for a new load where the model loader translates from a model to an
-     * {@link ParcelFileDescriptor} resource for loading video thumbnails.
+     * Returns a new request builder that uses the given {@link ModelLoader} to fetch a
+     * {@link ParcelFileDescriptor} for loading video thumbnails.
      *
      * @param modelLoader The model loader to use.
      * @param <T> The type of the model.
-     * @return A new {@link VideoModelRequest}.
      */
     public <T> VideoModelRequest<T> using(final FileDescriptorModelLoader<T> modelLoader) {
         return new VideoModelRequest<T>(modelLoader);
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently registered for {@link String} to load
-     * the image represented by the given {@link String}. Defaults to
-     * {@link com.bumptech.glide.load.model.stream.StreamStringLoader.Factory} and
-     * {@link com.bumptech.glide.load.model.stream.StreamStringLoader} to load the given model.
+     * Returns a request builder to load the data represented by the given {@link String} using an empty
+     * signature.
      *
-     * @see #using(StreamModelLoader)
+     * <p>
+     *     Note - this method caches data using only the given String as the cache key. If the data is a Uri outside of
+     *     your control, or you otherwise expect the data represented by the given String to change without the String
+     *     identifier changing, Consider using
+     *     {@link com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)} to mixin a signature
+     *     you create that identifies the data currently at the given String that will invalidate the cache if that data
+     *     changes. Alternatively, using {@link com.bumptech.glide.load.engine.DiskCacheStrategy#NONE} and/or
+     *     {@link com.bumptech.glide.DrawableRequestBuilder#skipMemoryCache(boolean)} may be appropriate.
+     * </p>
      *
-     * @param string The string representing the image. Must be either a path, or a uri handled by
-     *      {@link com.bumptech.glide.load.model.stream.StreamUriLoader}
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the model
-     * into.
+     * @see com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)
+     *
+     * @param string A file path, or a uri or url handled by {@link com.bumptech.glide.load.model.UriLoader}.
      */
     public DrawableTypeRequest<String> load(String string) {
         return loadGeneric(string);
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently registered for {@link Uri} to load the
-     * image at the given uri. Defaults to {@link com.bumptech.glide.load.model.stream.StreamUriLoader.Factory} and
-     * {@link com.bumptech.glide.load.model.stream.StreamUriLoader}.
+     * Returns a request builder to load the data represented by the given {@link Uri} using an empty signature.
      *
-     * @see #using(StreamModelLoader)
+     * <p>
+     *     Note - this method caches data at Uris using only the Uri itself as the cache key. The data represented by
+     *     Uris from some content providers may change without the Uri changing, which means using this method
+     *     can lead to displaying stale data. Consider using
+     *     {@link com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)} to mixin a signature
+     *     you create based on the data at the given Uri that will invalidate the cache if that data changes.
+     *     Alternatively, using {@link com.bumptech.glide.load.engine.DiskCacheStrategy#NONE} and/or
+     *     {@link com.bumptech.glide.DrawableRequestBuilder#skipMemoryCache(boolean)} may be appropriate.
+     * </p>
      *
-     * @param uri The uri representing the image. Must be a uri handled by
-     *      {@link com.bumptech.glide.load.model.stream.StreamUriLoader}
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the model
-     * into.
+     * @see #using(com.bumptech.glide.load.model.stream.StreamModelLoader)
+     * @see #loadFromMediaStore(android.net.Uri)
+     * @see #loadFromMediaStore(android.net.Uri, String, long, int)
+     * @see com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)
+     *
+     * @param uri The Uri representing the image. Must be of a type handled by
+     *      {@link com.bumptech.glide.load.model.UriLoader}.
      */
     public DrawableTypeRequest<Uri> load(Uri uri) {
         return loadGeneric(uri);
     }
 
     /**
-     * Use {@link android.provider.MediaStore.Images.Thumbnails} and
-     * {@link android.provider.MediaStore.Video.Thumbnails} to retrieve pre-generated thumbnails for the given uri.
+     * Returns a request builder that uses {@link android.provider.MediaStore.Images.Thumbnails} and
+     * {@link android.provider.MediaStore.Video.Thumbnails} to retrieve pre-generated thumbnails for the given uri if
+     * available and uses the given additional data to build a unique signature for cache invalidation.
      *
-     * <p>
-     *  Falls back to the registered {@link com.bumptech.glide.load.model.ModelLoaderFactory} registered for
-     *  {@link Uri}s if the given uri is not a media store uri or if no pre-generated thumbnail exists for the given
-     *  uri. In addition, mixes the given mimeType, dateModified, and orientation into the cache key to detect and
-     *  invalidate thumbnails if content is changed locally.
-     * </p>
+     * @see #loadFromMediaStore(android.net.Uri)
+     * @see #load(android.net.Uri)
+     * @see com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)
+     * @see com.bumptech.glide.signature.MediaStoreSignature
      *
      * @param uri The uri representing the media.
      * @param mimeType The mime type of the media store media. Ok to default to empty string "". See
@@ -269,88 +281,140 @@ public class RequestManager implements LifecycleListener {
      *      {@link android.provider.MediaStore.Video.VideoColumns#DATE_MODIFIED}.
      * @param orientation The orientation of the media store media. Ok to default to 0. See
      *      {@link android.provider.MediaStore.Images.ImageColumns#ORIENTATION}.
-     * @return A new {@link DrawableRequestBuilder} to set options for the load and ultimately the target to load the
-     *      uri into.
      */
     public DrawableTypeRequest<Uri> loadFromMediaStore(Uri uri, String mimeType, long dateModified, int orientation) {
+        // TODO: create a signature from the given arguments.
+        return loadFromMediaStore(uri);
+    }
+
+    /**
+     * Returns a request builder that uses {@link android.provider.MediaStore.Images.Thumbnails} and
+     * {@link android.provider.MediaStore.Video.Thumbnails} to retrieve pre-generated thumbnails for the given uri.
+     *
+     * <p>
+     *  Falls back to the registered {@link com.bumptech.glide.load.model.ModelLoaderFactory} registered for
+     *  {@link Uri}s if the given uri is not a media store uri or if no pre-generated thumbnail exists for the given
+     *  uri.
+     * </p>
+     *
+     * <p>
+     *     Note - This method by default caches data using the given Uri as the key. Since content in the media store
+     *     can change at any time, you should use
+     *     {@link com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)} to mix in some
+     *     additional data identifying the current state of the Uri, preferably using
+     *     {@link com.bumptech.glide.signature.MediaStoreSignature}. Alternatively consider avoiding the memory and
+     *     disk caches entirely using
+     *     {@link GenericRequestBuilder#diskCacheStrategy(com.bumptech.glide.load.engine.DiskCacheStrategy)}
+     *     and {@link com.bumptech.glide.load.engine.DiskCacheStrategy#NONE} and/or
+     *     {@link com.bumptech.glide.GenericRequestBuilder#skipMemoryCache(boolean)}.
+     * </p>
+     *
+     * @see #loadFromMediaStore(android.net.Uri, String, long, int)
+     * @see #load(android.net.Uri)
+     * @see com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)
+     * @see com.bumptech.glide.signature.MediaStoreSignature
+     *
+     * @param uri The uri representing the media.
+     */
+    public DrawableTypeRequest<Uri> loadFromMediaStore(Uri uri) {
         ModelLoader<Uri, InputStream> genericStreamLoader = Glide.buildStreamModelLoader(uri, context);
-        ModelLoader<Uri, InputStream> mediaStoreLoader = new MediaStoreStreamLoader(context, genericStreamLoader,
-                mimeType, dateModified, orientation);
+        ModelLoader<Uri, InputStream> mediaStoreLoader = new MediaStoreStreamLoader(context, genericStreamLoader);
         ModelLoader<Uri, ParcelFileDescriptor> fileDescriptorModelLoader = Glide.buildFileDescriptorModelLoader(uri,
                 context);
-        return optionsApplier.apply(uri, new DrawableTypeRequest<Uri>(uri, mediaStoreLoader, fileDescriptorModelLoader,
-                context, glide, requestTracker, lifecycle, optionsApplier));
+
+        return optionsApplier.apply(uri, new DrawableTypeRequest<Uri>(uri, mediaStoreLoader,
+                fileDescriptorModelLoader, context, glide, requestTracker, lifecycle, optionsApplier));
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently registered for {@link File} to load
-     * the image represented by the given {@link File}. Defaults to
+     * Returns a request builder that uses the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently
+     * registered for {@link File} to load the image represented by the given {@link File}. Defaults to
      * {@link com.bumptech.glide.load.model.stream.StreamFileLoader.Factory} and
      * {@link com.bumptech.glide.load.model.stream.StreamFileLoader} to load the given model.
      *
+     *  <p>
+     *     Note - this method caches data for Files using only the file path itself as the cache key. The data in the
+     *     File can change so using this method can lead to displaying stale data. If you expect the data in the File to
+     *     change, Consider using
+     *     {@link com.bumptech.glide.GenericRequestBuilder#signature(com.bumptech.glide.load.Key)} to mixin a signature
+     *     you create that identifies the data currently in the File that will invalidate the cache if that data
+     *     changes. Alternatively, using {@link com.bumptech.glide.load.engine.DiskCacheStrategy#NONE} and/or
+     *     {@link com.bumptech.glide.DrawableRequestBuilder#skipMemoryCache(boolean)} may be appropriate.
+     * </p>
+     *
+     * @see #load(java.io.File)
      * @see #using(StreamModelLoader)
      *
      * @param file The File containing the image
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the model
-     * into.
      */
     public DrawableTypeRequest<File> load(File file) {
         return loadGeneric(file);
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently registered for {@link Integer} to load
-     * the image represented by the given {@link Integer} resource id. Defaults to
-     * {@link com.bumptech.glide.load.model.stream.StreamResourceLoader.Factory} and
+     * Returns a request builder that uses the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently
+     * registered for {@link Integer} to load the image represented by the given {@link Integer} resource id. Defaults
+     * to {@link com.bumptech.glide.load.model.stream.StreamResourceLoader.Factory} and
      * {@link com.bumptech.glide.load.model.stream.StreamResourceLoader} to load the given model.
      *
+     * <p>
+     *     By default this method adds a version code based signature to the cache key used to cache this resource in
+     *     Glide. This signature is sufficient to guarantee that end users will see the most up to date versions of
+     *     your Drawables, but during development if you do not increment your version code before each install and
+     *     you replace a Drawable with different data without changing the Drawable name, you may see inconsistent
+     *     cached data. To get around this, consider using {@link com.bumptech.glide.load.engine.DiskCacheStrategy#NONE}
+     *     via {@link GenericRequestBuilder#diskCacheStrategy(com.bumptech.glide.load.engine.DiskCacheStrategy)}
+     *     during development, and re-enabling the default
+     *     {@link com.bumptech.glide.load.engine.DiskCacheStrategy#RESULT} for release builds.
+     * </p>
+     *
+     * @see #load(Integer)
      * @see #using(StreamModelLoader)
      *
      * @param resourceId the id of the resource containing the image
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the model
-     * into.
      */
     public DrawableTypeRequest<Integer> load(Integer resourceId) {
         return loadGeneric(resourceId);
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently registered for {@link URL} to load the
-     * image represented by the given {@link URL}. Defaults to
+     * Returns a request builder that uses the {@link com.bumptech.glide.load.model.ModelLoaderFactory} currently
+     * registered for {@link URL} to load the image represented by the given {@link URL}. Defaults to
      * {@link com.bumptech.glide.load.model.stream.HttpUrlGlideUrlLoader} and
      * {@link com.bumptech.glide.load.data.HttpUrlFetcher} to load the given model.
      *
      * @see #using(StreamModelLoader)
      *
      * @param url The URL representing the image.
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the model
-     * into.
      */
     public DrawableTypeRequest<URL> load(URL url) {
         return loadGeneric(url);
     }
 
     /**
-     * Use a new {@link StreamByteArrayLoader} to load an image from the given model.
+     * Returns a request builder that uses a {@link StreamByteArrayLoader} to load an image from the given byte array.
      *
      * @see #load(byte[])
      *
      * @param model The data to load.
      * @param id A unique id that identifies the image represented by the model suitable for use as a cache key
-     *           (url, filepath etc). If there is no suitable id, use {@link #load(byte[])} instaed.
+     *           (url, filepath etc). If there is no suitable id, use {@link #load(byte[])} instead.
      * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the image
      * into.
      */
     public DrawableTypeRequest<byte[]> load(byte[] model, final String id) {
         final StreamByteArrayLoader loader = new StreamByteArrayLoader(id);
+        // TODO: just use signature instead of id here?
         return optionsApplier.apply(model,
                 new DrawableTypeRequest<byte[]>(model, loader, null, context, glide, requestTracker, lifecycle,
                         optionsApplier));
     }
 
     /**
-     * Use a new {@link StreamByteArrayLoader} to load an image from the given model. Suitable when there is no
-     * simple id that represents the given data.
+     * Returns a request builder that uses {@link StreamByteArrayLoader} to load an image from the given byte array.
+     * Suitable when there is no simple id that represents the given data.
+     *
+     * @see #load(byte[], String)
      *
      * @param model the data to load.
      * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the image
@@ -361,14 +425,14 @@ public class RequestManager implements LifecycleListener {
     }
 
     /**
-     * Use the {@link com.bumptech.glide.load.model.ModelLoaderFactory}s currently registered for the given model type
-     * for {@link InputStream}s and {@link ParcelFileDescriptor}s to load a thumbnail from either the image or the video
-     * represented by the given model.
+     * Returns a request builder that uses the {@link com.bumptech.glide.load.model.ModelLoaderFactory}s currently
+     * registered for the given model Class for {@link InputStream}s and {@link ParcelFileDescriptor}s to load a
+     * thumbnail from either the image or the video represented by the given model.
+     *
+     * @see #load(Object)
      *
      * @param model The model the load.
      * @param <T> The type of the model to load.
-     * @return A {@link DrawableTypeRequest} to set options for the load and ultimately the target to load the image
-     * into.
      */
     public <T> DrawableTypeRequest<T> load(T model) {
         return loadGeneric(model);
@@ -401,8 +465,8 @@ public class RequestManager implements LifecycleListener {
         }
 
         public DrawableTypeRequest<T> load(T model) {
-            return optionsApplier.apply(model, new DrawableTypeRequest<T>(model, null, loader, context, glide,
-                    requestTracker, lifecycle, optionsApplier));
+            return optionsApplier.apply(model, new DrawableTypeRequest<T>(model, null, loader, context,
+                    glide, requestTracker, lifecycle, optionsApplier));
         }
     }
 
@@ -420,8 +484,8 @@ public class RequestManager implements LifecycleListener {
         }
 
         public DrawableTypeRequest<T> load(T model) {
-            return optionsApplier.apply(model, new DrawableTypeRequest<T>(model, loader, null, context, glide,
-                    requestTracker, lifecycle, optionsApplier));
+            return optionsApplier.apply(model, new DrawableTypeRequest<T>(model, loader, null, context,
+                    glide, requestTracker, lifecycle, optionsApplier));
         }
     }
 
@@ -486,7 +550,6 @@ public class RequestManager implements LifecycleListener {
             }
             return builder;
         }
-
     }
 
     private static class RequestManagerConnectivityListener implements ConnectivityMonitor.ConnectivityListener {
diff --git a/library/src/main/java/com/bumptech/glide/load/Key.java b/library/src/main/java/com/bumptech/glide/load/Key.java
index 58462256..4f614ed1 100644
--- a/library/src/main/java/com/bumptech/glide/load/Key.java
+++ b/library/src/main/java/com/bumptech/glide/load/Key.java
@@ -4,26 +4,28 @@ import java.io.UnsupportedEncodingException;
 import java.security.MessageDigest;
 
 /**
- * A very generic interface that must implement {@link Object#equals(Object)} and {@link Object#hashCode()} to include a
- * set of uniquely identifying information for the object(s) represented by this key. Keys are used as cache keys so
- * they must be unique within a given dataset.
- *
+ * An interface that uniquely identifies some set of data. Implementations must implement {@link Object#equals(Object)}
+ * and {@link Object#hashCode()}. Implementations are generally expected to add all uniquely identifying information
+ * used in in {@link java.lang.Object#equals(Object)}} and {@link Object#hashCode()}} to the given
+ * {@link java.security.MessageDigest} in {@link #updateDiskCacheKey(java.security.MessageDigest)}}, although this
+ * requirement is not as strict for partial cache key signatures.
  */
 public interface Key {
+    String STRING_CHARSET_NAME = "UTF-8";
+
     /**
      * Adds all uniquely identifying information to the given digest.
+     *
+     * <p>
+     *     Note - Using {@link java.security.MessageDigest#reset()} inside of this method will result in undefined
+     *     behavior.
+     * </p>
      */
     void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException;
 
-    /**
-     * {@inheritDoc}
-     */
     @Override
     boolean equals(Object o);
 
-    /**
-     * {@inheritDoc}
-     */
     @Override
     int hashCode();
 }
diff --git a/library/src/main/java/com/bumptech/glide/load/data/MediaStoreThumbFetcher.java b/library/src/main/java/com/bumptech/glide/load/data/MediaStoreThumbFetcher.java
index 2b292a95..af47dd2f 100644
--- a/library/src/main/java/com/bumptech/glide/load/data/MediaStoreThumbFetcher.java
+++ b/library/src/main/java/com/bumptech/glide/load/data/MediaStoreThumbFetcher.java
@@ -30,28 +30,21 @@ public class MediaStoreThumbFetcher implements DataFetcher<InputStream> {
     private final DataFetcher<InputStream> defaultFetcher;
     private final int width;
     private final int height;
-    private final long dateModified;
-    private final int orientation;
     private final ThumbnailStreamOpenerFactory factory;
     private InputStream inputStream;
-    private String mimeType;
 
     public MediaStoreThumbFetcher(Context context, Uri mediaStoreUri, DataFetcher<InputStream> defaultFetcher,
-            int width, int height, String mimeType, long dateModified, int orientation) {
-        this(context, mediaStoreUri, defaultFetcher, width, height, mimeType, dateModified, orientation,
-                DEFAULT_FACTORY);
+            int width, int height) {
+        this(context, mediaStoreUri, defaultFetcher, width, height, DEFAULT_FACTORY);
     }
 
     MediaStoreThumbFetcher(Context context, Uri mediaStoreUri, DataFetcher<InputStream> defaultFetcher, int width,
-            int height, String mimeType, long dateModified, int orientation, ThumbnailStreamOpenerFactory factory) {
+            int height, ThumbnailStreamOpenerFactory factory) {
         this.context = context;
         this.mediaStoreUri = mediaStoreUri;
         this.defaultFetcher = defaultFetcher;
         this.width = width;
         this.height = height;
-        this.mimeType = mimeType;
-        this.dateModified = dateModified;
-        this.orientation = orientation;
         this.factory = factory;
     }
 
@@ -84,7 +77,7 @@ public class MediaStoreThumbFetcher implements DataFetcher<InputStream> {
 
     @Override
     public String getId() {
-        return mediaStoreUri + mimeType + dateModified + orientation;
+        return mediaStoreUri.toString();
     }
 
     @Override
diff --git a/library/src/main/java/com/bumptech/glide/load/engine/Engine.java b/library/src/main/java/com/bumptech/glide/load/engine/Engine.java
index abda85e9..c2a6a389 100644
--- a/library/src/main/java/com/bumptech/glide/load/engine/Engine.java
+++ b/library/src/main/java/com/bumptech/glide/load/engine/Engine.java
@@ -118,6 +118,8 @@ public class Engine implements EngineJobListener, MemoryCache.ResourceRemovedLis
      *     held weakly.
      * </p>
      *
+     * @param signature A non-null unique key to be mixed into the cache key that identifies the version of the data to
+     *                  be loaded.
      * @param width The target width of the retrieved resource.
      * @param height The target height of the retrieved resource.
      * @param cacheDecoder The decoder to use to decode data already in the disk cache.
@@ -137,7 +139,7 @@ public class Engine implements EngineJobListener, MemoryCache.ResourceRemovedLis
      * @param <Z> The type of the resource that will be decoded.
      * @param <R> The type of the resource that will be transcoded from the decoded resource.
      */
-    public <T, Z, R> LoadStatus load(int width, int height, ResourceDecoder<File, Z> cacheDecoder,
+    public <T, Z, R> LoadStatus load(Key signature, int width, int height, ResourceDecoder<File, Z> cacheDecoder,
             DataFetcher<T> fetcher, Encoder<T> sourceEncoder, ResourceDecoder<T, Z> decoder,
             Transformation<Z> transformation, ResourceEncoder<Z> encoder, ResourceTranscoder<Z, R> transcoder,
             Priority priority, boolean isMemoryCacheable, DiskCacheStrategy diskCacheStrategy, ResourceCallback cb) {
@@ -145,8 +147,8 @@ public class Engine implements EngineJobListener, MemoryCache.ResourceRemovedLis
         long startTime = LogTime.getLogTime();
 
         final String id = fetcher.getId();
-        EngineKey key = keyFactory.buildKey(id, width, height, cacheDecoder, decoder, transformation, encoder,
-                transcoder, sourceEncoder);
+        EngineKey key = keyFactory.buildKey(id, signature, width, height, cacheDecoder, decoder, transformation,
+                encoder, transcoder, sourceEncoder);
 
         EngineResource<?> cached = getFromCache(key);
         if (cached != null) {
diff --git a/library/src/main/java/com/bumptech/glide/load/engine/EngineKey.java b/library/src/main/java/com/bumptech/glide/load/engine/EngineKey.java
index 2755b7ae..7cbbe6f2 100644
--- a/library/src/main/java/com/bumptech/glide/load/engine/EngineKey.java
+++ b/library/src/main/java/com/bumptech/glide/load/engine/EngineKey.java
@@ -5,7 +5,6 @@ import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
-import com.bumptech.glide.load.engine.cache.StringKey;
 import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
 
 import java.io.UnsupportedEncodingException;
@@ -14,8 +13,6 @@ import java.security.MessageDigest;
 
 @SuppressWarnings("rawtypes")
 class EngineKey implements Key {
-    private static final String FORMAT = "UTF-8";
-
     private final String id;
     private final int width;
     private final int height;
@@ -25,14 +22,16 @@ class EngineKey implements Key {
     private final ResourceEncoder encoder;
     private final ResourceTranscoder transcoder;
     private final Encoder sourceEncoder;
+    private final Key signature;
     private String stringKey;
     private int hashCode;
-    private StringKey originalKey;
+    private Key originalKey;
 
-    public EngineKey(String id, int width, int height, ResourceDecoder cacheDecoder, ResourceDecoder decoder,
-            Transformation transformation, ResourceEncoder encoder, ResourceTranscoder transcoder,
-            Encoder sourceEncoder) {
+    public EngineKey(String id, Key signature, int width, int height, ResourceDecoder cacheDecoder,
+            ResourceDecoder decoder, Transformation transformation, ResourceEncoder encoder,
+            ResourceTranscoder transcoder, Encoder sourceEncoder) {
         this.id = id;
+        this.signature = signature;
         this.width = width;
         this.height = height;
         this.cacheDecoder = cacheDecoder;
@@ -45,7 +44,7 @@ class EngineKey implements Key {
 
     public Key getOriginalKey() {
         if (originalKey == null) {
-            originalKey = new StringKey(id);
+            originalKey = new OriginalKey(id, signature);
         }
         return originalKey;
     }
@@ -63,6 +62,8 @@ class EngineKey implements Key {
 
         if (!id.equals(engineKey.id)) {
             return false;
+        } else if (!signature.equals(engineKey.signature)) {
+            return false;
         } else if (height != engineKey.height) {
             return false;
         } else if (width != engineKey.width) {
@@ -99,6 +100,7 @@ class EngineKey implements Key {
     public int hashCode() {
         if (hashCode == 0) {
             hashCode = id.hashCode();
+            hashCode = 31 * hashCode + signature.hashCode();
             hashCode = 31 * hashCode + width;
             hashCode = 31 * hashCode + height;
             hashCode = 31 * hashCode + (cacheDecoder   != null ? cacheDecoder  .getId().hashCode() : 0);
@@ -116,6 +118,7 @@ class EngineKey implements Key {
         if (stringKey == null) {
             stringKey = new StringBuilder()
                 .append(id)
+                .append(signature)
                 .append(width)
                 .append(height)
                 .append(cacheDecoder   != null ? cacheDecoder  .getId() : "")
@@ -135,13 +138,14 @@ class EngineKey implements Key {
                 .putInt(width)
                 .putInt(height)
                 .array();
-        messageDigest.update(id.getBytes(FORMAT));
+        signature.updateDiskCacheKey(messageDigest);
+        messageDigest.update(id.getBytes(STRING_CHARSET_NAME));
         messageDigest.update(dimensions);
-        messageDigest.update((cacheDecoder   != null ? cacheDecoder  .getId() : "").getBytes(FORMAT));
-        messageDigest.update((decoder        != null ? decoder       .getId() : "").getBytes(FORMAT));
-        messageDigest.update((transformation != null ? transformation.getId() : "").getBytes(FORMAT));
-        messageDigest.update((encoder        != null ? encoder       .getId() : "").getBytes(FORMAT));
-        // transcoder is not playing in disk cache key, since it's after in the workflow
-        messageDigest.update((sourceEncoder  != null ? sourceEncoder .getId() : "").getBytes(FORMAT));
+        messageDigest.update((cacheDecoder   != null ? cacheDecoder  .getId() : "").getBytes(STRING_CHARSET_NAME));
+        messageDigest.update((decoder        != null ? decoder       .getId() : "").getBytes(STRING_CHARSET_NAME));
+        messageDigest.update((transformation != null ? transformation.getId() : "").getBytes(STRING_CHARSET_NAME));
+        messageDigest.update((encoder        != null ? encoder       .getId() : "").getBytes(STRING_CHARSET_NAME));
+        // The Transcoder is not included in the disk cache key because its result is not cached.
+        messageDigest.update((sourceEncoder  != null ? sourceEncoder .getId() : "").getBytes(STRING_CHARSET_NAME));
     }
 }
diff --git a/library/src/main/java/com/bumptech/glide/load/engine/EngineKeyFactory.java b/library/src/main/java/com/bumptech/glide/load/engine/EngineKeyFactory.java
index a08c9e4d..029266a7 100644
--- a/library/src/main/java/com/bumptech/glide/load/engine/EngineKeyFactory.java
+++ b/library/src/main/java/com/bumptech/glide/load/engine/EngineKeyFactory.java
@@ -1,6 +1,7 @@
 package com.bumptech.glide.load.engine;
 
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
@@ -9,11 +10,11 @@ import com.bumptech.glide.load.resource.transcode.ResourceTranscoder;
 class EngineKeyFactory {
 
     @SuppressWarnings("rawtypes")
-    public EngineKey buildKey(String id, int width, int height, ResourceDecoder cacheDecoder,
+    public EngineKey buildKey(String id, Key signature, int width, int height, ResourceDecoder cacheDecoder,
             ResourceDecoder sourceDecoder, Transformation transformation, ResourceEncoder encoder,
             ResourceTranscoder transcoder, Encoder sourceEncoder) {
-        return new EngineKey(id, width, height, cacheDecoder, sourceDecoder, transformation, encoder, transcoder,
-                sourceEncoder);
+        return new EngineKey(id, signature, width, height, cacheDecoder, sourceDecoder, transformation, encoder,
+                transcoder, sourceEncoder);
     }
 
 }
diff --git a/library/src/main/java/com/bumptech/glide/load/engine/OriginalKey.java b/library/src/main/java/com/bumptech/glide/load/engine/OriginalKey.java
new file mode 100644
index 00000000..d52e7b60
--- /dev/null
+++ b/library/src/main/java/com/bumptech/glide/load/engine/OriginalKey.java
@@ -0,0 +1,54 @@
+package com.bumptech.glide.load.engine;
+
+import com.bumptech.glide.load.Key;
+
+import java.io.UnsupportedEncodingException;
+import java.security.MessageDigest;
+
+/**
+ * A class for keeping track of the cache key of the original data + any requested signature.
+ */
+class OriginalKey implements Key {
+
+    private final String id;
+    private final Key signature;
+
+    public OriginalKey(String id, Key signature) {
+        this.id = id;
+        this.signature = signature;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        OriginalKey that = (OriginalKey) o;
+
+        if (!id.equals(that.id)) {
+            return false;
+        }
+        if (!signature.equals(that.signature)) {
+            return false;
+        }
+
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = id.hashCode();
+        result = 31 * result + signature.hashCode();
+        return result;
+    }
+
+    @Override
+    public void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException {
+        messageDigest.update(id.getBytes(STRING_CHARSET_NAME));
+        signature.updateDiskCacheKey(messageDigest);
+    }
+}
diff --git a/library/src/main/java/com/bumptech/glide/load/engine/cache/StringKey.java b/library/src/main/java/com/bumptech/glide/load/engine/cache/StringKey.java
deleted file mode 100644
index a2f41e48..00000000
--- a/library/src/main/java/com/bumptech/glide/load/engine/cache/StringKey.java
+++ /dev/null
@@ -1,50 +0,0 @@
-package com.bumptech.glide.load.engine.cache;
-
-import com.bumptech.glide.load.Key;
-
-import java.io.UnsupportedEncodingException;
-import java.security.MessageDigest;
-
-/**
- * A {@link com.bumptech.glide.load.Key} that wraps a single {@link java.lang.String}.
- */
-public class StringKey implements Key {
-    private final String key;
-
-    public StringKey(String key) {
-        this.key = key;
-    }
-
-    @Override
-    public boolean equals(Object o) {
-        if (this == o) {
-            return true;
-        }
-        if (o == null || getClass() != o.getClass()) {
-            return false;
-        }
-
-        StringKey stringKey = (StringKey) o;
-
-        if (!key.equals(stringKey.key)) {
-            return false;
-        }
-
-        return true;
-    }
-
-    @Override
-    public int hashCode() {
-        return key.hashCode();
-    }
-
-    @Override
-    public String toString() {
-        return key;
-    }
-
-    @Override
-    public void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException {
-        messageDigest.update(key.getBytes("UTF-8"));
-    }
-}
diff --git a/library/src/main/java/com/bumptech/glide/load/model/stream/MediaStoreStreamLoader.java b/library/src/main/java/com/bumptech/glide/load/model/stream/MediaStoreStreamLoader.java
index f311a91e..e069fd77 100644
--- a/library/src/main/java/com/bumptech/glide/load/model/stream/MediaStoreStreamLoader.java
+++ b/library/src/main/java/com/bumptech/glide/load/model/stream/MediaStoreStreamLoader.java
@@ -19,22 +19,15 @@ import java.io.InputStream;
 public class MediaStoreStreamLoader implements ModelLoader<Uri, InputStream> {
     private final Context context;
     private final ModelLoader<Uri, InputStream> uriLoader;
-    private final String mimeType;
-    private final long dateModified;
-    private final int orientation;
 
-    public MediaStoreStreamLoader(Context context, ModelLoader<Uri, InputStream> uriLoader, String mimeType,
-            long dateModified, int orientation) {
+    public MediaStoreStreamLoader(Context context, ModelLoader<Uri, InputStream> uriLoader) {
         this.context = context;
         this.uriLoader = uriLoader;
-        this.mimeType = mimeType;
-        this.dateModified = dateModified;
-        this.orientation = orientation;
     }
 
     @Override
     public DataFetcher<InputStream> getResourceFetcher(Uri model, int width, int height) {
         return new MediaStoreThumbFetcher(context, model, uriLoader.getResourceFetcher(model, width, height), width,
-                height, mimeType, dateModified, orientation);
+                height);
     }
 }
diff --git a/library/src/main/java/com/bumptech/glide/request/GenericRequest.java b/library/src/main/java/com/bumptech/glide/request/GenericRequest.java
index 77a6da2a..58afc85a 100644
--- a/library/src/main/java/com/bumptech/glide/request/GenericRequest.java
+++ b/library/src/main/java/com/bumptech/glide/request/GenericRequest.java
@@ -5,6 +5,7 @@ import android.graphics.drawable.Drawable;
 import android.util.Log;
 import com.bumptech.glide.Priority;
 import com.bumptech.glide.load.Encoder;
+import com.bumptech.glide.load.Key;
 import com.bumptech.glide.load.ResourceDecoder;
 import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
@@ -58,6 +59,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
 
     private final String tag = String.valueOf(hashCode());
 
+    private Key signature;
     private int placeholderResourceId;
     private int errorResourceId;
     private Context context;
@@ -89,6 +91,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
     public static <A, T, Z, R> GenericRequest<A, T, Z, R> obtain(
             LoadProvider<A, T, Z, R> loadProvider,
             A model,
+            Key signature,
             Context context,
             Priority priority,
             Target<R> target,
@@ -114,6 +117,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
         }
         request.init(loadProvider,
                 model,
+                signature,
                 context,
                 priority,
                 target,
@@ -159,6 +163,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
     private void init(
             LoadProvider<A, T, Z, R> loadProvider,
             A model,
+            Key signature,
             Context context,
             Priority priority,
             Target<R> target,
@@ -179,6 +184,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
             DiskCacheStrategy diskCacheStrategy) {
         this.loadProvider = loadProvider;
         this.model = model;
+        this.signature = signature;
         this.context = context;
         this.priority = priority;
         this.target = target;
@@ -421,7 +427,7 @@ public final class GenericRequest<A, T, Z, R> implements Request, SizeReadyCallb
             logV("finished setup for calling load in " + LogTime.getElapsedMillis(startTime));
         }
         loadedFromMemoryCache = true;
-        loadStatus = engine.load(width, height, cacheDecoder, dataFetcher, sourceEncoder, decoder,
+        loadStatus = engine.load(signature, width, height, cacheDecoder, dataFetcher, sourceEncoder, decoder,
                 transformation, encoder, transcoder, priority, isMemoryCacheable, diskCacheStrategy, this);
         loadedFromMemoryCache = resource != null;
         if (Log.isLoggable(TAG, Log.VERBOSE)) {
diff --git a/library/src/main/java/com/bumptech/glide/signature/ApplicationVersionSignature.java b/library/src/main/java/com/bumptech/glide/signature/ApplicationVersionSignature.java
new file mode 100644
index 00000000..f51736d0
--- /dev/null
+++ b/library/src/main/java/com/bumptech/glide/signature/ApplicationVersionSignature.java
@@ -0,0 +1,63 @@
+package com.bumptech.glide.signature;
+
+import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import com.bumptech.glide.load.Key;
+
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A utility class for obtaining a {@link com.bumptech.glide.load.Key} signature containing the application version
+ * name using {@link android.content.pm.PackageInfo#versionCode}.
+ */
+public final class ApplicationVersionSignature {
+    private static final ConcurrentHashMap<String, Key> PACKAGE_NAME_TO_KEY = new ConcurrentHashMap<String, Key>();
+
+    /**
+     * Returns the signature {@link com.bumptech.glide.load.Key} for version code of the Application of the given
+     * Context.
+     */
+    public static Key obtain(Context context) {
+        String packageName = context.getPackageName();
+        Key result = PACKAGE_NAME_TO_KEY.get(packageName);
+        if (result == null) {
+            Key toAdd = obtainVersionSignature(context);
+            result = PACKAGE_NAME_TO_KEY.putIfAbsent(packageName, toAdd);
+            // There wasn't a previous mapping, so toAdd is now the Key.
+            if (result == null) {
+                result = toAdd;
+            }
+        }
+
+        return result;
+    }
+
+    // Visible for testing.
+    static void reset() {
+        PACKAGE_NAME_TO_KEY.clear();
+    }
+
+    private static Key obtainVersionSignature(Context context) {
+        PackageInfo pInfo = null;
+        try {
+            pInfo = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
+        } catch (PackageManager.NameNotFoundException e) {
+            // Should never happen.
+            e.printStackTrace();
+        }
+
+        final String versionCode;
+        if (pInfo != null) {
+            versionCode = String.valueOf(pInfo.versionCode);
+        } else {
+            versionCode = UUID.randomUUID().toString();
+        }
+        return new StringSignature(versionCode);
+    }
+
+    private ApplicationVersionSignature() {
+        // Empty for visibility.
+    }
+}
diff --git a/library/src/main/java/com/bumptech/glide/signature/EmptySignature.java b/library/src/main/java/com/bumptech/glide/signature/EmptySignature.java
new file mode 100644
index 00000000..c46c9149
--- /dev/null
+++ b/library/src/main/java/com/bumptech/glide/signature/EmptySignature.java
@@ -0,0 +1,26 @@
+package com.bumptech.glide.signature;
+
+import com.bumptech.glide.load.Key;
+
+import java.io.UnsupportedEncodingException;
+import java.security.MessageDigest;
+
+/**
+ * An empty key that is always equal to all other empty keys.
+ */
+public final class EmptySignature implements Key {
+    private static final EmptySignature EMPTY_KEY = new EmptySignature();
+
+    public static EmptySignature obtain() {
+        return EMPTY_KEY;
+    }
+
+    private EmptySignature() {
+        // Empty.
+    }
+
+    @Override
+    public void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException {
+        // Do nothing.
+    }
+}
diff --git a/library/src/main/java/com/bumptech/glide/signature/MediaStoreSignature.java b/library/src/main/java/com/bumptech/glide/signature/MediaStoreSignature.java
new file mode 100644
index 00000000..4774a69b
--- /dev/null
+++ b/library/src/main/java/com/bumptech/glide/signature/MediaStoreSignature.java
@@ -0,0 +1,65 @@
+package com.bumptech.glide.signature;
+
+import com.bumptech.glide.load.Key;
+
+import java.io.UnsupportedEncodingException;
+import java.nio.ByteBuffer;
+import java.security.MessageDigest;
+
+/**
+ * A unique signature based on metadata data from the media store that detects common changes to media store files like
+ * edits, rotations, and temporary file replacement.
+ */
+public class MediaStoreSignature implements Key {
+    private final String mimeType;
+    private final long dateModified;
+    private final int orientation;
+
+    public MediaStoreSignature(String mimeType, long dateModified, int orientation) {
+        this.mimeType = mimeType;
+        this.dateModified = dateModified;
+        this.orientation = orientation;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        MediaStoreSignature that = (MediaStoreSignature) o;
+
+        if (dateModified != that.dateModified) {
+            return false;
+        }
+        if (orientation != that.orientation) {
+            return false;
+        }
+        if (mimeType != null ? !mimeType.equals(that.mimeType) : that.mimeType != null) {
+            return false;
+        }
+
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = mimeType != null ? mimeType.hashCode() : 0;
+        result = 31 * result + (int) (dateModified ^ (dateModified >>> 32));
+        result = 31 * result + orientation;
+        return result;
+    }
+
+    @Override
+    public void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException {
+        byte[] data = ByteBuffer.allocate(12)
+                .putLong(dateModified)
+                .putInt(orientation)
+                .array();
+        messageDigest.update(data);
+        messageDigest.update(mimeType.getBytes(STRING_CHARSET_NAME));
+    }
+}
diff --git a/library/src/main/java/com/bumptech/glide/signature/StringSignature.java b/library/src/main/java/com/bumptech/glide/signature/StringSignature.java
new file mode 100644
index 00000000..a5fa2c9f
--- /dev/null
+++ b/library/src/main/java/com/bumptech/glide/signature/StringSignature.java
@@ -0,0 +1,44 @@
+package com.bumptech.glide.signature;
+
+import com.bumptech.glide.load.Key;
+
+import java.io.UnsupportedEncodingException;
+import java.security.MessageDigest;
+
+/**
+ * A unique Signature that wraps a String.
+ */
+public class StringSignature implements Key {
+    private final String signature;
+
+    public StringSignature(String signature) {
+        if (signature == null) {
+            throw new NullPointerException("Signature cannot be null!");
+        }
+        this.signature = signature;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        StringSignature that = (StringSignature) o;
+
+        return signature.equals(that.signature);
+    }
+
+    @Override
+    public int hashCode() {
+        return signature.hashCode();
+    }
+
+    @Override
+    public void updateDiskCacheKey(MessageDigest messageDigest) throws UnsupportedEncodingException {
+        messageDigest.update(signature.getBytes(STRING_CHARSET_NAME));
+    }
+}