PendingValue.java
/*
* Copyright 2023 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 androidx.camera.view;
import static androidx.camera.core.impl.utils.Threads.checkMainThread;
import static androidx.core.util.Preconditions.checkState;
import static java.util.Objects.requireNonNull;
import android.os.Build;
import androidx.annotation.MainThread;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.RequiresApi;
import androidx.arch.core.util.Function;
import androidx.camera.core.CameraControl;
import androidx.camera.core.impl.utils.futures.Futures;
import androidx.concurrent.futures.CallbackToFutureAdapter;
import com.google.common.util.concurrent.ListenableFuture;
/**
* Pending value assignment that wait for event like camera initialization.
*
* <p> For example, one cannot call {@link CameraControl#setZoomRatio} before camera initialization
* completes. To work around this, in {@link CameraController} when app calls
* {@link CameraController#setZoomRatio}, we will cache the value with this class and propagate it
* when {@link CameraControl} becomes ready.
*/
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
class PendingValue<T> {
@Nullable
private T mValue;
@Nullable
private ListenableFuture<Void> mListenableFuture;
@Nullable
private CallbackToFutureAdapter.Completer<Void> mCompleter;
/**
* Assigns the pending value.
*
* @return a {@link ListenableFuture} that completes when the assignment completes.
*/
@MainThread
ListenableFuture<Void> setValue(@NonNull T value) {
checkMainThread();
if (mListenableFuture != null) {
checkState(!mListenableFuture.isDone(),
"#setValue() is called after the value is propagated.");
// Cancel the previous ListenableFuture.
mListenableFuture.cancel(false);
}
// Track the pending value and the ListenableFuture.
mValue = value;
mListenableFuture = CallbackToFutureAdapter.getFuture(completer -> {
mCompleter = completer;
return "PendingValue " + value;
});
return mListenableFuture;
}
/**
* Propagates the value if a pending value exists.
*
* <p> This method no-ops if there is no pending value.
*/
@MainThread
void propagateIfHasValue(Function<T, ListenableFuture<Void>> setValueFunction) {
checkMainThread();
if (mValue != null) {
Futures.propagate(setValueFunction.apply(mValue), requireNonNull(mCompleter));
}
}
}