Merge changes from topic "shanh-back-api"

* changes:
  Provide OnBackInvokedDispatcher from Activity, View and Dialog
  Introduce IOnBackInvokedCallback and OnBackInvokedDispatcher

core/api/current.txt

@@ -3995,7 +3995,7 @@ package android.app {
     method @Deprecated public void onTabUnselected(android.app.ActionBar.Tab, android.app.FragmentTransaction);
   }
 
-  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
+  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.OnBackInvokedDispatcherOwner android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
     ctor public Activity();
     method public void addContentView(android.view.View, android.view.ViewGroup.LayoutParams);
     method public void closeContextMenu();
@@ -4038,6 +4038,7 @@ package android.app {
     method public int getMaxNumPictureInPictureActions();
     method public final android.media.session.MediaController getMediaController();
     method @NonNull public android.view.MenuInflater getMenuInflater();
+    method @Nullable public android.view.OnBackInvokedDispatcher getOnBackInvokedDispatcher();
     method public final android.app.Activity getParent();
     method @Nullable public android.content.Intent getParentActivityIntent();
     method public android.content.SharedPreferences getPreferences(int);
@@ -4916,7 +4917,7 @@ package android.app {
     method public void onDateSet(android.widget.DatePicker, int, int, int);
   }
 
-  public class Dialog implements android.content.DialogInterface android.view.KeyEvent.Callback android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
+  public class Dialog implements android.content.DialogInterface android.view.KeyEvent.Callback android.view.OnBackInvokedDispatcherOwner android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
     ctor public Dialog(@NonNull @UiContext android.content.Context);
     ctor public Dialog(@NonNull @UiContext android.content.Context, @StyleRes int);
     ctor protected Dialog(@NonNull @UiContext android.content.Context, boolean, @Nullable android.content.DialogInterface.OnCancelListener);
@@ -4936,6 +4937,7 @@ package android.app {
     method @NonNull @UiContext public final android.content.Context getContext();
     method @Nullable public android.view.View getCurrentFocus();
     method @NonNull public android.view.LayoutInflater getLayoutInflater();
+    method @Nullable public android.view.OnBackInvokedDispatcher getOnBackInvokedDispatcher();
     method @Nullable public final android.app.Activity getOwnerActivity();
     method @Nullable public final android.view.SearchEvent getSearchEvent();
     method public final int getVolumeControlStream();
@@ -49478,6 +49480,22 @@ package android.view {
     field public int toolType;
   }
 
+  public interface OnBackInvokedCallback {
+    method public default void onBackInvoked();
+  }
+
+  public abstract class OnBackInvokedDispatcher {
+    ctor public OnBackInvokedDispatcher();
+    method public abstract void registerOnBackInvokedCallback(@NonNull android.view.OnBackInvokedCallback, int);
+    method public abstract void unregisterOnBackInvokedCallback(@NonNull android.view.OnBackInvokedCallback);
+    field public static final int PRIORITY_DEFAULT = 0; // 0x0
+    field public static final int PRIORITY_OVERLAY = 1000000; // 0xf4240
+  }
+
+  public interface OnBackInvokedDispatcherOwner {
+    method @Nullable public android.view.OnBackInvokedDispatcher getOnBackInvokedDispatcher();
+  }
+
   public interface OnReceiveContentListener {
     method @Nullable public android.view.ContentInfo onReceiveContent(@NonNull android.view.View, @NonNull android.view.ContentInfo);
   }
@@ -49901,7 +49919,7 @@ package android.view {
     field @NonNull public static final android.os.Parcelable.Creator<android.view.VerifiedMotionEvent> CREATOR;
   }
 
-  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback {
+  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback android.view.OnBackInvokedDispatcherOwner {
     ctor public View(android.content.Context);
     ctor public View(android.content.Context, @Nullable android.util.AttributeSet);
     ctor public View(android.content.Context, @Nullable android.util.AttributeSet, int);
@@ -50105,6 +50123,7 @@ package android.view {
     method @IdRes public int getNextFocusLeftId();
     method @IdRes public int getNextFocusRightId();
     method @IdRes public int getNextFocusUpId();
+    method @Nullable public android.view.OnBackInvokedDispatcher getOnBackInvokedDispatcher();
     method public android.view.View.OnFocusChangeListener getOnFocusChangeListener();
     method @ColorInt public int getOutlineAmbientShadowColor();
     method public android.view.ViewOutlineProvider getOutlineProvider();

core/api/module-lib-current.txt

@@ -9,7 +9,7 @@ package android {
 
 package android.app {
 
-  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
+  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.OnBackInvokedDispatcherOwner android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
     method public final boolean addDumpable(@NonNull android.util.Dumpable);
   }
 

core/api/removed.txt

@@ -513,7 +513,7 @@ package android.util {
 
 package android.view {
 
-  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback {
+  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback android.view.OnBackInvokedDispatcherOwner {
     method protected void initializeFadingEdge(android.content.res.TypedArray);
     method protected void initializeScrollbars(android.content.res.TypedArray);
   }

core/api/system-current.txt

@@ -444,7 +444,7 @@ package android.accounts {
 
 package android.app {
 
-  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
+  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.OnBackInvokedDispatcherOwner android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
     method public void convertFromTranslucent();
     method public boolean convertToTranslucent(android.app.Activity.TranslucentConversionListener, android.app.ActivityOptions);
     method @Deprecated public boolean isBackgroundVisibleBehind();

core/api/test-current.txt

@@ -101,7 +101,7 @@ package android.animation {
 
 package android.app {
 
-  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
+  @UiContext public class Activity extends android.view.ContextThemeWrapper implements android.content.ComponentCallbacks2 android.view.KeyEvent.Callback android.view.LayoutInflater.Factory2 android.view.OnBackInvokedDispatcherOwner android.view.View.OnCreateContextMenuListener android.view.Window.Callback {
     method public void onMovedToDisplay(int, android.content.res.Configuration);
   }
 
@@ -2779,7 +2779,7 @@ package android.view {
     method public void setView(@NonNull android.view.View, @NonNull android.view.WindowManager.LayoutParams);
   }
 
-  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback {
+  @UiThread public class View implements android.view.accessibility.AccessibilityEventSource android.graphics.drawable.Drawable.Callback android.view.KeyEvent.Callback android.view.OnBackInvokedDispatcherOwner {
     method public android.view.View getTooltipView();
     method public boolean isAutofilled();
     method public static boolean isDefaultFocusHighlightEnabled();

core/java/android/app/Activity.java

@@ -111,6 +111,8 @@ import android.view.Menu;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.MotionEvent;
+import android.view.OnBackInvokedDispatcher;
+import android.view.OnBackInvokedDispatcherOwner;
 import android.view.RemoteAnimationDefinition;
 import android.view.SearchEvent;
 import android.view.View;
@@ -736,7 +738,8 @@ public class Activity extends ContextThemeWrapper
         Window.Callback, KeyEvent.Callback,
         OnCreateContextMenuListener, ComponentCallbacks2,
         Window.OnWindowDismissedCallback,
-        ContentCaptureManager.ContentCaptureClient {
+        ContentCaptureManager.ContentCaptureClient,
+        OnBackInvokedDispatcherOwner {
     private static final String TAG = "Activity";
     private static final boolean DEBUG_LIFECYCLE = false;
 
@@ -8672,4 +8675,22 @@ public class Activity extends ContextThemeWrapper
             return (w != null && w.peekDecorView() != null);
         }
     }
+
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} instance associated with the window that this
+     * activity is attached to.
+     *
+     * Returns null if the activity is not attached to a window with a decor.
+     */
+    @Nullable
+    @Override
+    public OnBackInvokedDispatcher getOnBackInvokedDispatcher() {
+        if (mWindow != null) {
+            View decorView = mWindow.getDecorView();
+            if (decorView != null) {
+                return decorView.getOnBackInvokedDispatcher();
+            }
+        }
+        return null;
+    }
 }

core/java/android/app/Dialog.java

@@ -52,6 +52,8 @@ import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.MotionEvent;
+import android.view.OnBackInvokedDispatcher;
+import android.view.OnBackInvokedDispatcherOwner;
 import android.view.SearchEvent;
 import android.view.View;
 import android.view.View.OnCreateContextMenuListener;
@@ -94,7 +96,8 @@ import java.lang.ref.WeakReference;
  * </div>
  */
 public class Dialog implements DialogInterface, Window.Callback,
-        KeyEvent.Callback, OnCreateContextMenuListener, Window.OnWindowDismissedCallback {
+        KeyEvent.Callback, OnCreateContextMenuListener, Window.OnWindowDismissedCallback,
+        OnBackInvokedDispatcherOwner {
     private static final String TAG = "Dialog";
     @UnsupportedAppUsage
     private Activity mOwnerActivity;
@@ -1439,4 +1442,22 @@ public class Dialog implements DialogInterface, Window.Callback,
             }
         }
     }
+
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} instance associated with the window that this
+     * dialog is attached to.
+     *
+     * Returns null if the dialog is not attached to a window with a decor.
+     */
+    @Nullable
+    @Override
+    public OnBackInvokedDispatcher getOnBackInvokedDispatcher() {
+        if (mWindow != null) {
+            View decorView = mWindow.getDecorView();
+            if (decorView != null) {
+                return decorView.getOnBackInvokedDispatcher();
+            }
+        }
+        return null;
+    }
 }

core/java/android/view/OnBackInvokedCallback.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2022 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.view;
+
+import android.app.Activity;
+import android.app.Dialog;
+
+/**
+ * Interface for applications to register back invocation callbacks. This allows the client
+ * to customize various back behaviors by overriding the corresponding callback methods.
+ *
+ * Callback instances can be added to and removed from {@link OnBackInvokedDispatcher}, held
+ * by classes that implement {@link OnBackInvokedDispatcherOwner} (such as {@link Activity},
+ * {@link Dialog} and {@link View}).
+ *
+ * Under the hood callbacks are registered at window level. When back is triggered,
+ * callbacks on the in-focus window are invoked in reverse order in which they are added
+ * within the same priority. Between different pirorities, callbacks with higher priority
+ * are invoked first.
+ *
+ * See {@link OnBackInvokedDispatcher#registerOnBackInvokedCallback(OnBackInvokedCallback, int)}
+ * for specifying callback priority.
+ */
+public interface OnBackInvokedCallback {
+   /**
+    * Called when a back gesture has been started, or back button has been pressed down.
+    *
+    * @hide
+    */
+    default void onBackStarted() { };
+
+    /**
+     * Called on back gesture progress.
+     *
+     * @param touchX Absolute X location of the touch point.
+     * @param touchY Absolute Y location of the touch point.
+     * @param progress Value between 0 and 1 on how far along the back gesture is.
+     *
+     * @hide
+     */
+    // TODO(b/210539672): combine back progress params into BackEvent.
+    default void onBackProgressed(int touchX, int touchY, float progress) { };
+
+    /**
+     * Called when a back gesture or back button press has been cancelled.
+     *
+     * @hide
+     */
+    default void onBackCancelled() { };
+
+    /**
+     * Called when a back gesture has been completed and committed, or back button pressed
+     * has been released and committed.
+     */
+    default void onBackInvoked() { };
+}

core/java/android/view/OnBackInvokedDispatcher.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2022 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.view;
+
+import android.annotation.IntDef;
+import android.annotation.NonNull;
+import android.annotation.SuppressLint;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Dispatcher to register {@link OnBackInvokedCallback} instances for handling
+ * back invocations.
+ *
+ * It also provides interfaces to update the attributes of {@link OnBackInvokedCallback}.
+ * Attribute updates are proactively pushed to the window manager if they change the dispatch
+ * target (a.k.a. the callback to be invoked next), or its behavior.
+ */
+public abstract class OnBackInvokedDispatcher {
+    /** @hide */
+    @IntDef({
+            PRIORITY_DEFAULT,
+            PRIORITY_OVERLAY,
+    })
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface Priority{}
+
+    /**
+     * Priority level of {@link OnBackInvokedCallback}s for overlays such as menus and
+     * navigation drawers that should receive back dispatch before non-overlays.
+     */
+    public static final int PRIORITY_OVERLAY = 1000000;
+
+    /**
+     * Default priority level of {@link OnBackInvokedCallback}s.
+     */
+    public static final int PRIORITY_DEFAULT = 0;
+
+    /**
+     * Registers a {@link OnBackInvokedCallback}.
+     *
+     * Within the same priority level, callbacks are invoked in the reverse order in which
+     * they are registered. Higher priority callbacks are invoked before lower priority ones.
+     *
+     * @param callback The callback to be registered. If the callback instance has been already
+     *                 registered, the existing instance (no matter its priority) will be
+     *                 unregistered and registered again.
+     * @param priority The priority of the callback.
+     */
+    @SuppressLint("SamShouldBeLast")
+    public abstract void registerOnBackInvokedCallback(
+            @NonNull OnBackInvokedCallback callback, @Priority int priority);
+
+    /**
+     * Unregisters a {@link OnBackInvokedCallback}.
+     *
+     * @param callback The callback to be unregistered. Does nothing if the callback has not been
+     *                 registered.
+     */
+    public abstract void unregisterOnBackInvokedCallback(@NonNull OnBackInvokedCallback callback);
+}

core/java/android/view/OnBackInvokedDispatcherOwner.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2022 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.view;
+
+import android.annotation.Nullable;
+
+/**
+ * A class that provides an {@link OnBackInvokedDispatcher} that allows you to register
+ * an {@link OnBackInvokedCallback} for handling the system back invocation behavior.
+ */
+public interface OnBackInvokedDispatcherOwner {
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} that should dispatch the back invocation
+     * to its registered {@link OnBackInvokedCallback}s.
+     * Returns null when the root view is not attached to a window or a view tree with a decor.
+     */
+    @Nullable
+    OnBackInvokedDispatcher getOnBackInvokedDispatcher();
+}

core/java/android/view/View.java

@@ -834,7 +834,7 @@ import java.util.function.Predicate;
  */
 @UiThread
 public class View implements Drawable.Callback, KeyEvent.Callback,
-        AccessibilityEventSource {
+        AccessibilityEventSource, OnBackInvokedDispatcherOwner {
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
     private static final boolean DBG = false;
 
@@ -31276,4 +31276,23 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
         }
         return null;
     }
+
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} instance of the window this view is attached to.
+     *
+     * @return The {@link OnBackInvokedDispatcher} or {@code null} if the view is neither attached
+     *         to a window or a view tree with a decor.
+     */
+    @Nullable
+    public OnBackInvokedDispatcher getOnBackInvokedDispatcher() {
+        ViewParent parent = getParent();
+        if (parent instanceof View) {
+            return ((View) parent).getOnBackInvokedDispatcher();
+        } else if (parent instanceof ViewRootImpl) {
+            // Get the fallback dispatcher on {@link ViewRootImpl} if the view tree doesn't have
+            // a {@link com.android.internal.policy.DecorView}.
+            return ((ViewRootImpl) parent).getOnBackInvokedDispatcher();
+        }
+        return null;
+    }
 }

core/java/android/view/ViewRootImpl.java

@@ -192,6 +192,7 @@ import android.view.contentcapture.MainContentCaptureSession;
 import android.view.inputmethod.InputMethodManager;
 import android.widget.Scroller;
 import android.window.ClientWindowFrames;
+import android.window.WindowOnBackInvokedDispatcher;
 
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
@@ -308,6 +309,12 @@ public final class ViewRootImpl implements ViewParent,
             new ArrayList<>();
     private @SurfaceControl.BufferTransform
             int mPreviousTransformHint = SurfaceControl.BUFFER_TRANSFORM_IDENTITY;
+    /**
+     * The fallback {@link OnBackInvokedDispatcher} when the window doesn't have a decor view.
+     */
+    private WindowOnBackInvokedDispatcher mFallbackOnBackInvokedDispatcher =
+            new WindowOnBackInvokedDispatcher();
+
     /**
      * Callback for notifying about global configuration changes.
      */
@@ -871,6 +878,7 @@ public final class ViewRootImpl implements ViewParent,
         mFastScrollSoundEffectsEnabled = audioManager.areNavigationRepeatSoundEffectsEnabled();
 
         mScrollCaptureRequestTimeout = SCROLL_CAPTURE_REQUEST_TIMEOUT_MILLIS;
+        mFallbackOnBackInvokedDispatcher.attachToWindow(mWindowSession, mWindow);
     }
 
     public static void addFirstDrawHandler(Runnable callback) {
@@ -1120,6 +1128,9 @@ public final class ViewRootImpl implements ViewParent,
                     if (pendingInsetsController != null) {
                         pendingInsetsController.replayAndAttach(mInsetsController);
                     }
+                    ((RootViewSurfaceTaker) mView)
+                            .provideWindowOnBackInvokedDispatcher()
+                            .attachToWindow(mWindowSession, mWindow);
                 }
 
                 try {
@@ -10634,7 +10645,7 @@ public final class ViewRootImpl implements ViewParent,
        }
        mBLASTDrawConsumer = consume;
        return true;
-   }
+    }
 
     boolean wasRelayoutRequested() {
         return mRelayoutRequested;
@@ -10644,4 +10655,16 @@ public final class ViewRootImpl implements ViewParent,
        mForceNextWindowRelayout = true;
        scheduleTraversals();
     }
+
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} on the decor view if one exists, or the
+     * fallback {@link OnBackInvokedDispatcher} instance.
+     */
+    @Nullable
+    public OnBackInvokedDispatcher getOnBackInvokedDispatcher() {
+        if (mView instanceof RootViewSurfaceTaker) {
+            return ((RootViewSurfaceTaker) mView).provideWindowOnBackInvokedDispatcher();
+        }
+        return mFallbackOnBackInvokedDispatcher;
+    }
 }

core/java/android/window/WindowOnBackInvokedDispatcher.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2021 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.NonNull;
+import android.view.IWindow;
+import android.view.IWindowSession;
+import android.view.OnBackInvokedCallback;
+import android.view.OnBackInvokedDispatcher;
+
+/**
+ * Provides window based implementation of {@link OnBackInvokedDispatcher}.
+ *
+ * Callbacks with higher priorities receive back dispatching first.
+ * Within the same priority, callbacks receive back dispatching in the reverse order
+ * in which they are added.
+ *
+ * When the top priority callback is updated, the new callback is propagated to the Window Manager
+ * if the window the instance is associated with has been attached. It is allowed to register /
+ * unregister {@link OnBackInvokedCallback}s before the window is attached, although callbacks
+ * will not receive dispatches until window attachment.
+ *
+ * @hide
+ */
+public class WindowOnBackInvokedDispatcher extends OnBackInvokedDispatcher {
+    private IWindowSession mWindowSession;
+    private IWindow mWindow;
+
+    /**
+     * Sends the pending top callback (if one exists) to WM when the view root
+     * is attached a window.
+     */
+    public void attachToWindow(@NonNull IWindowSession windowSession, @NonNull IWindow window) {
+        mWindowSession = windowSession;
+        mWindow = window;
+        // TODO(b/209867448): Send the top callback to WM (if one exists).
+    }
+
+    /** Detaches the dispatcher instance from its window. */
+    public void detachFromWindow() {
+        mWindow = null;
+        mWindowSession = null;
+    }
+
+    @Override
+    public void registerOnBackInvokedCallback(
+            @NonNull OnBackInvokedCallback callback, @Priority int priority) {
+        // TODO(b/209867448): To be implemented.
+    }
+
+    @Override
+    public void unregisterOnBackInvokedCallback(
+            @NonNull OnBackInvokedCallback callback) {
+        // TODO(b/209867448): To be implemented.
+    }
+
+    /** Clears all registered callbacks on the instance. */
+    public void clear() {
+        // TODO(b/209867448): To be implemented.
+    }
+}

core/java/com/android/internal/policy/DecorView.java

@@ -87,6 +87,7 @@ import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.MotionEvent;
+import android.view.OnBackInvokedDispatcher;
 import android.view.PendingInsetsController;
 import android.view.ThreadedRenderer;
 import android.view.View;
@@ -108,6 +109,7 @@ import android.view.animation.AnimationUtils;
 import android.view.animation.Interpolator;
 import android.widget.FrameLayout;
 import android.widget.PopupWindow;
+import android.window.WindowOnBackInvokedDispatcher;
 
 import com.android.internal.R;
 import com.android.internal.graphics.drawable.BackgroundBlurDrawable;
@@ -294,6 +296,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         return true;
     };
     private Consumer<Boolean> mCrossWindowBlurEnabledListener;
+    private final WindowOnBackInvokedDispatcher mOnBackInvokedDispatcher;
 
     DecorView(Context context, int featureId, PhoneWindow window,
             WindowManager.LayoutParams params) {
@@ -322,6 +325,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         initResizingPaints();
 
         mLegacyNavigationBarBackgroundPaint.setColor(Color.BLACK);
+        mOnBackInvokedDispatcher = new WindowOnBackInvokedDispatcher();
     }
 
     void setBackgroundFallback(@Nullable Drawable fallbackDrawable) {
@@ -1869,6 +1873,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         }
 
         mPendingInsetsController.detach();
+        mOnBackInvokedDispatcher.detachFromWindow();
     }
 
     @Override
@@ -1913,6 +1918,11 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         return mPendingInsetsController;
     }
 
+    @Override
+    public WindowOnBackInvokedDispatcher provideWindowOnBackInvokedDispatcher() {
+        return mOnBackInvokedDispatcher;
+    }
+
     private ActionMode createActionMode(
             int type, ActionMode.Callback2 callback, View originatingView) {
         switch (type) {
@@ -2367,6 +2377,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
                 }
             }
         }
+        mOnBackInvokedDispatcher.clear();
     }
 
     @Override
@@ -2648,6 +2659,15 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         }
     }
 
+    /**
+     * Returns the {@link OnBackInvokedDispatcher} on the decor view.
+     */
+    @Override
+    @Nullable
+    public OnBackInvokedDispatcher getOnBackInvokedDispatcher() {
+        return mOnBackInvokedDispatcher;
+    }
+
     @Override
     public String toString() {
         return "DecorView@" + Integer.toHexString(this.hashCode()) + "["

core/java/com/android/internal/view/RootViewSurfaceTaker.java

@@ -15,11 +15,12 @@
  */
 package com.android.internal.view;
 
+import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.view.InputQueue;
 import android.view.PendingInsetsController;
 import android.view.SurfaceHolder;
-import android.view.WindowInsetsController;
+import android.window.WindowOnBackInvokedDispatcher;
 
 /** hahahah */
 public interface RootViewSurfaceTaker {
@@ -30,4 +31,6 @@ public interface RootViewSurfaceTaker {
     InputQueue.Callback willYouTakeTheInputQueue();
     void onRootViewScrollYChanged(int scrollY);
     @Nullable PendingInsetsController providePendingInsetsController();
+    /** @hide */
+    @NonNull WindowOnBackInvokedDispatcher provideWindowOnBackInvokedDispatcher();
 }