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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.camera.async;
import com.android.camera.util.Callback;
import com.google.common.base.Function;
import com.google.common.base.Supplier;
import com.google.common.util.concurrent.MoreExecutors;
import java.util.List;
import java.util.concurrent.Executor;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nonnull;
import javax.annotation.ParametersAreNonnullByDefault;
/**
* Helper methods for {@link Observable}.
*/
@ParametersAreNonnullByDefault
public class Observables {
private static final SafeCloseable NOOP_CALLBACK_HANDLE = new SafeCloseable() {
@Override
public void close() {
// Do Nothing.
}
};
private Observables() {
}
/**
* Transforms an observable with a function.
*
* @return The transformed observable.
*/
public static <F, T> Observable<T> transform(final Observable<F> input,
final Function<F, T> function) {
return new Observable<T>() {
@Nonnull
@Override
public T get() {
return function.apply(input.get());
}
@CheckReturnValue
@Nonnull
@Override
public SafeCloseable addCallback(Runnable callback, Executor executor) {
return input.addCallback(callback, executor);
}
};
}
/**
* @return An observable which recomputes its output every time an input changes.
*/
public static <T> Observable<T> transform(final List<? extends Observable<?>> inputs,
final Supplier<T> output) {
return ObservableCombiner.transform(inputs, output);
}
/**
* Transforms a set of observables with a function.
*
* @return The transformed observable.
*/
public static <F, T> Observable<T> transform(final List<? extends Observable<F>> input,
Function<List<F>, T> function) {
return ObservableCombiner.transform(input, function);
}
/**
* @return An observable which has the given constant value.
*/
@Nonnull
public static <T> Observable<T> of(final @Nonnull T constant) {
return new Observable<T>() {
@Nonnull
@Override
public T get() {
return constant;
}
@CheckReturnValue
@Nonnull
@Override
public SafeCloseable addCallback(Runnable callback, Executor executor) {
return NOOP_CALLBACK_HANDLE;
}
};
}
@Nonnull
@CheckReturnValue
public static <T> SafeCloseable addThreadSafeCallback(final Observable<T> observable,
final Updatable<T> callback) {
return observable.addCallback(new Runnable() {
@Override
public void run() {
callback.update(observable.get());
}
}, MoreExecutors.directExecutor());
}
}
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