Prevent back navigation not working after activity re-created

When recreating the Activity, if the window is preserved, we would set
the actual dispatcher from the preserved window to the new Activiy's
proxy dispatcher, and expect the new callback could be re-registered
in the recreating flow.

This CL clears the old callbacks of the preserved dispatcher before it
attach to the new proxy dispatcher, this could prevent it access the
wrong top callback after other new callbacks have been unregistered.

Also provide dump log for WindowOnBackInvokedDispatcher.

Bug: 259500250
Test: atest BackNavigationTests
Change-Id: Idc9a6a95f5669a009762570d7bc9acc2c538e4cb

core/java/android/view/ViewRootImpl.java

@@ -8692,6 +8692,8 @@ public final class ViewRootImpl implements ViewParent,
 
         mInsetsController.dump(prefix, writer);
 
+        mOnBackInvokedDispatcher.dump(prefix, writer);
+
         writer.println(prefix + "View Hierarchy:");
         dumpViewHierarchy(innerPrefix, writer, mView);
     }

core/java/android/window/ImeOnBackInvokedDispatcher.java

@@ -211,6 +211,12 @@ public class ImeOnBackInvokedDispatcher implements OnBackInvokedDispatcher, Parc
         IOnBackInvokedCallback getIOnBackInvokedCallback() {
             return mIOnBackInvokedCallback;
         }
+
+        @Override
+        public String toString() {
+            return "ImeCallback=ImeOnBackInvokedCallback@" + mId
+                    + " Callback=" + mIOnBackInvokedCallback;
+        }
     }
 
     /**

core/java/android/window/ProxyOnBackInvokedDispatcher.java

@@ -180,16 +180,7 @@ public class ProxyOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
                 return;
             }
             clearCallbacksOnDispatcher();
-            if (actualDispatcher instanceof ProxyOnBackInvokedDispatcher) {
-                // We don't want to nest ProxyDispatchers, so if we are given on, we unwrap its
-                // actual dispatcher.
-                // This can happen when an Activity is recreated but the Window is preserved (e.g.
-                // when going from split-screen back to single screen)
-                mActualDispatcher =
-                        ((ProxyOnBackInvokedDispatcher) actualDispatcher).mActualDispatcher;
-            } else {
-                mActualDispatcher = actualDispatcher;
-            }
+            mActualDispatcher = actualDispatcher;
             transferCallbacksToDispatcher();
         }
     }

core/java/android/window/WindowOnBackInvokedDispatcher.java

@@ -29,6 +29,7 @@ import android.util.Log;
 import android.view.IWindow;
 import android.view.IWindowSession;
 
+import java.io.PrintWriter;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -232,6 +233,26 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
         return Checker.isOnBackInvokedCallbackEnabled(mChecker.getContext());
     }
 
+    /**
+     * Dump information about this WindowOnBackInvokedDispatcher
+     * @param prefix the prefix that will be prepended to each line of the produced output
+     * @param writer the writer that will receive the resulting text
+     */
+    public void dump(String prefix, PrintWriter writer) {
+        String innerPrefix = prefix + "    ";
+        writer.println(prefix + "WindowOnBackDispatcher:");
+        if (mAllCallbacks.isEmpty()) {
+            writer.println(prefix + "<None>");
+            return;
+        }
+
+        writer.println(innerPrefix + "Top Callback: " + getTopCallback());
+        writer.println(innerPrefix + "Callbacks: ");
+        mAllCallbacks.forEach((callback, priority) -> {
+            writer.println(innerPrefix + "  Callback: " + callback + " Priority=" + priority);
+        });
+    }
+
     static class OnBackInvokedCallbackWrapper extends IOnBackInvokedCallback.Stub {
         private final WeakReference<OnBackInvokedCallback> mCallback;
 

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

@@ -378,8 +378,12 @@ public class PhoneWindow extends Window implements MenuBuilder.Callback {
             // window, as we'll be skipping the addView in handleResumeActivity(), and
             // the token will not be updated as for a new window.
             getAttributes().token = preservedWindow.getAttributes().token;
-            mProxyOnBackInvokedDispatcher.setActualDispatcher(
-                    preservedWindow.getOnBackInvokedDispatcher());
+            final ViewRootImpl viewRoot = mDecor.getViewRootImpl();
+            if (viewRoot != null) {
+                // Clear the old callbacks and attach to the new window.
+                viewRoot.getOnBackInvokedDispatcher().clear();
+                onViewRootImplSet(viewRoot);
+            }
         }
         // Even though the device doesn't support picture-in-picture mode,
         // an user can force using it through developer options.