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/*
* Copyright (C) 2024 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 android.window;
import android.annotation.FlaggedApi;
import android.annotation.NonNull;
import android.app.Activity;
import android.util.ArrayMap;
import com.android.window.flags.Flags;
import java.lang.ref.WeakReference;
/**
* Utility class providing {@link OnBackInvokedCallback}s to override the default behavior when
* system back is invoked. e.g. {@link Activity#finish}
*
* <p>By registering these callbacks with the {@link OnBackInvokedDispatcher}, the system can
* trigger specific behaviors and play corresponding ahead-of-time animations when the back
* gesture is invoked.
*
* <p>For example, to trigger the {@link Activity#moveTaskToBack} behavior:
* <pre>
* OnBackInvokedDispatcher dispatcher = activity.getOnBackInvokedDispatcher();
* dispatcher.registerOnBackInvokedCallback(
* OnBackInvokedDispatcher.PRIORITY_DEFAULT,
* SystemOnBackInvokedCallbacks.moveTaskToBackCallback(activity));
* </pre>
*/
@SuppressWarnings("SingularCallback")
@FlaggedApi(Flags.FLAG_PREDICTIVE_BACK_SYSTEM_OVERRIDE_CALLBACK)
public final class SystemOnBackInvokedCallbacks {
private static final OverrideCallbackFactory<Activity> sMoveTaskToBackFactory = new
MoveTaskToBackCallbackFactory();
private static final OverrideCallbackFactory<Activity> sFinishAndRemoveTaskFactory = new
FinishAndRemoveTaskCallbackFactory();
private SystemOnBackInvokedCallbacks() {
throw new UnsupportedOperationException("This is a utility class and cannot be "
+ "instantiated");
}
/**
* <p>Get a callback to triggers {@link Activity#moveTaskToBack(boolean)} on the associated
* {@link Activity}, moving the task containing the activity to the background. The system
* will play the corresponding transition animation, regardless of whether the activity
* is the root activity of the task.</p>
*
* @param activity The associated {@link Activity}
* @see Activity#moveTaskToBack(boolean)
*/
@FlaggedApi(Flags.FLAG_PREDICTIVE_BACK_SYSTEM_OVERRIDE_CALLBACK)
@NonNull
public static OnBackInvokedCallback moveTaskToBackCallback(@NonNull Activity activity) {
return sMoveTaskToBackFactory.getOverrideCallback(activity);
}
/**
* <p>Get a callback to triggers {@link Activity#finishAndRemoveTask()} on the associated
* {@link Activity}. If the activity is the root activity of its task, the entire task
* will be removed from the recents task. The activity will be finished in all cases.
* The system will play the corresponding transition animation.</p>
*
* @param activity The associated {@link Activity}
* @see Activity#finishAndRemoveTask()
*/
@FlaggedApi(Flags.FLAG_PREDICTIVE_BACK_SYSTEM_OVERRIDE_CALLBACK)
@NonNull
public static OnBackInvokedCallback finishAndRemoveTaskCallback(@NonNull Activity activity) {
return sFinishAndRemoveTaskFactory.getOverrideCallback(activity);
}
/**
* Abstract factory for creating system override {@link SystemOverrideOnBackInvokedCallback}
* instances.
*
* <p>Concrete implementations of this factory are responsible for creating callbacks that
* override the default system back navigation behavior. These callbacks should be used
* exclusively for system overrides and should never be invoked directly.</p>
*/
private abstract static class OverrideCallbackFactory<TYPE> {
private final ArrayMap<WeakReference<TYPE>,
WeakReference<SystemOverrideOnBackInvokedCallback>> mObjectMap = new ArrayMap<>();
protected abstract SystemOverrideOnBackInvokedCallback createCallback(
@NonNull TYPE context);
@NonNull SystemOverrideOnBackInvokedCallback getOverrideCallback(@NonNull TYPE object) {
if (object == null) {
throw new NullPointerException("Input object cannot be null");
}
synchronized (mObjectMap) {
WeakReference<SystemOverrideOnBackInvokedCallback> callback = null;
for (int i = mObjectMap.size() - 1; i >= 0; --i) {
final WeakReference<TYPE> next = mObjectMap.keyAt(i);
if (next.get() == object) {
callback = mObjectMap.get(next);
break;
}
}
if (callback != null) {
return callback.get();
}
final SystemOverrideOnBackInvokedCallback contextCallback = createCallback(object);
if (contextCallback != null) {
mObjectMap.put(new WeakReference<>(object),
new WeakReference<>(contextCallback));
}
return contextCallback;
}
}
}
private static class MoveTaskToBackCallbackFactory extends OverrideCallbackFactory<Activity> {
@Override
protected SystemOverrideOnBackInvokedCallback createCallback(Activity activity) {
final WeakReference<Activity> activityRef = new WeakReference<>(activity);
return new SystemOverrideOnBackInvokedCallback() {
@Override
public void onBackInvoked() {
if (activityRef.get() != null) {
activityRef.get().moveTaskToBack(true /* nonRoot */);
}
}
@Override
public int overrideBehavior() {
return OVERRIDE_MOVE_TASK_TO_BACK;
}
};
}
}
private static class FinishAndRemoveTaskCallbackFactory extends
OverrideCallbackFactory<Activity> {
@Override
protected SystemOverrideOnBackInvokedCallback createCallback(Activity activity) {
final WeakReference<Activity> activityRef = new WeakReference<>(activity);
return new SystemOverrideOnBackInvokedCallback() {
@Override
public void onBackInvoked() {
if (activityRef.get() != null) {
activityRef.get().finishAndRemoveTask();
}
}
@Override
public int overrideBehavior() {
return OVERRIDE_FINISH_AND_REMOVE_TASK;
}
};
}
}
}
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