1 files changed, 54 insertions, 56 deletions

diff --git a/android/arch/paging/ContiguousDataSource.java b/android/arch/paging/ContiguousDataSource.java
index be9da200..afcc208c 100644
--- a/android/arch/paging/ContiguousDataSource.java
+++ b/android/arch/paging/ContiguousDataSource.java
@@ -26,65 +26,21 @@ import java.util.List;
 /** @hide */
 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
 public abstract class ContiguousDataSource<Key, Value> extends DataSource<Key, Value> {
+    /**
+     * Number of items that this DataSource can provide in total, or COUNT_UNDEFINED.
+     *
+     * @return number of items that this DataSource can provide in total, or COUNT_UNDEFINED
+     * if difficult or undesired to compute.
+     */
+    public int countItems() {
+        return COUNT_UNDEFINED;
+    }
+
     @Override
     boolean isContiguous() {
         return true;
     }
 
-    void loadInitial(Key key, int pageSize, boolean enablePlaceholders,
-            PageResult.Receiver<Key, Value> receiver) {
-        NullPaddedList<Value> initial = loadInitial(key, pageSize, enablePlaceholders);
-        if (initial != null) {
-            receiver.onPageResult(new PageResult<>(
-                    PageResult.INIT,
-                    new Page<Key, Value>(initial.mList),
-                    initial.getLeadingNullCount(),
-                    initial.getTrailingNullCount(),
-                    initial.getPositionOffset()));
-        } else {
-            receiver.onPageResult(new PageResult<Key, Value>(
-                    PageResult.INIT, null, 0, 0, 0));
-        }
-    }
-
-    void loadAfter(int currentEndIndex, @NonNull Value currentEndItem, int pageSize,
-            PageResult.Receiver<Key, Value> receiver) {
-        List<Value> list = loadAfter(currentEndIndex, currentEndItem, pageSize);
-
-        Page<Key, Value> page = list != null
-                ? new Page<Key, Value>(list) : null;
-
-        receiver.postOnPageResult(new PageResult<>(
-                PageResult.APPEND, page, 0, 0, 0));
-    }
-
-    void loadBefore(int currentBeginIndex, @NonNull Value currentBeginItem, int pageSize,
-            PageResult.Receiver<Key, Value> receiver) {
-        List<Value> list = loadBefore(currentBeginIndex, currentBeginItem, pageSize);
-
-        Page<Key, Value> page = list != null
-                ? new Page<Key, Value>(list) : null;
-
-        receiver.postOnPageResult(new PageResult<>(
-                PageResult.PREPEND, page, 0, 0, 0));
-    }
-
-    /**
-     * Get the key from either the position, or item, or null if position/item invalid.
-     * <p>
-     * Position may not match passed item's position - if trying to query the key from a position
-     * that isn't yet loaded, a fallback item (last loaded item accessed) will be passed.
-     */
-    abstract Key getKey(int position, Value item);
-
-    @Nullable
-    abstract List<Value> loadAfterImpl(int currentEndIndex,
-            @NonNull Value currentEndItem, int pageSize);
-
-    @Nullable
-    abstract List<Value> loadBeforeImpl(int currentBeginIndex,
-            @NonNull Value currentBeginItem, int pageSize);
-
     /** @hide */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     @WorkerThread
@@ -92,7 +48,21 @@ public abstract class ContiguousDataSource<Key, Value> extends DataSource<Key, V
     public abstract NullPaddedList<Value> loadInitial(
             Key key, int initialLoadSize, boolean enablePlaceholders);
 
-    /** @hide */
+    /**
+     * Load data after the given position / item.
+     * <p>
+     * It's valid to return a different list size than the page size, if it's easier for this data
+     * source. It is generally safer to increase number loaded than reduce.
+     *
+     * @param currentEndIndex Load items after this index, starting with currentEndIndex + 1.
+     * @param currentEndItem  Load items after this item, can be used for precise querying based on
+     *                        item contents.
+     * @param pageSize        Suggested number of items to load.
+     * @return List of items, starting at position currentEndIndex + 1. Null if the data source is
+     * no longer valid, and should not be queried again.
+     *
+     * @hide
+     */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     @WorkerThread
     @Nullable
@@ -108,7 +78,24 @@ public abstract class ContiguousDataSource<Key, Value> extends DataSource<Key, V
         return list;
     }
 
-    /** @hide */
+    @Nullable
+    abstract List<Value> loadAfterImpl(int currentEndIndex,
+            @NonNull Value currentEndItem, int pageSize);
+
+    /**
+     * Load data before the given position / item.
+     * <p>
+     * It's valid to return a different list size than the page size, if it's easier for this data
+     * source. It is generally safer to increase number loaded than reduce.
+     *
+     * @param currentBeginIndex Load items before this index, starting with currentBeginIndex - 1.
+     * @param currentBeginItem  Load items after this item, can be used for precise querying based
+     *                          on item contents.
+     * @param pageSize          Suggested number of items to load.
+     * @return List of items, in descending order, starting at position currentBeginIndex - 1.
+     *
+     * @hide
+     */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     @WorkerThread
     @Nullable
@@ -124,4 +111,15 @@ public abstract class ContiguousDataSource<Key, Value> extends DataSource<Key, V
         return list;
 
     }
+
+    @Nullable
+    abstract List<Value> loadBeforeImpl(int currentBeginIndex,
+            @NonNull Value currentBeginItem, int pageSize);
+
+    /**
+     * Get the key from either the position, or item. Position may not match passed item's position,
+     * if trying to query the key from a position that isn't yet loaded, so a fallback item must be
+     * used.
+     */
+    abstract Key getKey(int position, Value item);
 }