Add views added to the WindowManager into the presentation view tree. (#6043)

The default WindowManager implementation in Android's Presentation is
delegating addView/removeView/updateViewLayout calls to the global
WindowManager.
This can result in a crash when an embedded view is trying to e.g show a
PopupWindow.

This change adds a custom WindowManager that overrides
addView (and removeView/updateViewLayout) and adds the view to the
presentation's view tree.

Note that views might keep a reference to the window manager which
might be an issue when we move a view from one virtual display to
another (due to a resize). For this reason when re-sizing we are not
creating a new window manager for the new presentation, but updating the
window manager's references to be relevant for the new presentation and
re-use it.

Author: amirh

shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java

@@ -7,24 +7,69 @@
 import android.annotation.TargetApi;
 import android.app.Presentation;
 import android.content.Context;
+import android.content.ContextWrapper;
+import android.graphics.Rect;
 import android.os.Build;
 import android.os.Bundle;
-import android.view.Display;
-import android.view.View;
-import android.view.WindowManager;
+import android.util.Log;
+import android.view.*;
 import android.widget.FrameLayout;
 
+import java.lang.reflect.*;
+
+import static android.content.Context.WINDOW_SERVICE;
+
+/*
+ * A presentation used for hosting a single Android view in a virtual display.
+ *
+ * This presentation overrides the WindowManager's addView/removeView/updateViewLayout methods, such that views added
+ * directly to the WindowManager are added as part of the presentation's view hierarchy (to mFakeWindowRootView).
+ *
+ * The view hierarchy for the presentation is as following:
+ *
+ *          mRootView
+ *         /         \
+ *        /           \
+ *       /             \
+ *   mContainer       mState.mFakeWindowRootView
+ *      |
+ *   EmbeddedView
+ */
 @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
 class SingleViewPresentation extends Presentation {
+
+    /*
+     * When an embedded view is resized in Flutterverse we move the Android view to a new virtual display
+     * that has the new size. This class keeps the presentation state that moves with the view to the presentation of
+     * the new virtual display.
+     */
+    static class PresentationState {
+        // The Android view we are embedding in the Flutter app.
+        private PlatformView mView;
+
+        // The InvocationHandler for a WindowManager proxy. This is essentially the custom window manager for the
+        // presentation.
+        private WindowManagerHandler mWindowManagerHandler;
+
+        // Contains views that were added directly to the window manager (e.g android.widget.PopupWindow).
+        private FakeWindowViewGroup mFakeWindowRootView;
+    }
+
     private final PlatformViewFactory mViewFactory;
 
-    private PlatformView mView;
+    // This is the view id assigned by the Flutter framework to the embedded view, we keep it here
+    // so when we create the platform we can tell it its view id.
     private int mViewId;
 
-    // As the root view of a display cannot be detached, we use this mContainer
-    // as the root, and attach mView to it. This allows us to detach mView.
+    // The root view for the presentation, it has 2 childs: mContainer which contains the embedded view, and
+    // mFakeWindowRootView which contains views that were added directly to the presentation's window manager.
+    private FrameLayout mRootView;
+
+    // Contains the embedded platform view (mView.getView()) when it is attached to the presentation.
     private FrameLayout mContainer;
 
+    private PresentationState mState;
+
     /**
      * Creates a presentation that will use the view factory to create a new
      * platform view in the presentation's onCreate, and attach it.
@@ -33,6 +78,7 @@ public SingleViewPresentation(Context outerContext, Display display, PlatformVie
         super(outerContext, display);
         mViewFactory = viewFactory;
         mViewId = viewId;
+        mState = new PresentationState();
         getWindow().setFlags(
                 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
@@ -46,10 +92,10 @@ public SingleViewPresentation(Context outerContext, Display display, PlatformVie
      * <p>The display's density must match the density of the context used
      * when the view was created.
      */
-    public SingleViewPresentation(Context outerContext, Display display, PlatformView view) {
+    public SingleViewPresentation(Context outerContext, Display display, PresentationState state) {
         super(outerContext, display);
         mViewFactory = null;
-        mView = view;
+        mState = state;
         getWindow().setFlags(
                 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
@@ -59,22 +105,195 @@ public SingleViewPresentation(Context outerContext, Display display, PlatformVie
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-        if (mView == null) {
-            mView = mViewFactory.create(getContext(), mViewId);
+        if (mState.mFakeWindowRootView == null) {
+            mState.mFakeWindowRootView = new FakeWindowViewGroup(getContext());
         }
+        if (mState.mWindowManagerHandler == null) {
+            WindowManager windowManagerDelegate = (WindowManager) getContext().getSystemService(WINDOW_SERVICE);
+            mState.mWindowManagerHandler = new WindowManagerHandler(windowManagerDelegate, mState.mFakeWindowRootView);
+        }
+
         mContainer = new FrameLayout(getContext());
-        mContainer.addView(mView.getView());
-        setContentView(mContainer);
+        PresentationContext context = new PresentationContext(getContext(), mState.mWindowManagerHandler);
+
+        if (mState.mView == null) {
+            mState.mView = mViewFactory.create(context, mViewId);
+        }
+
+        mContainer.addView(mState.mView.getView());
+        mRootView = new FrameLayout(getContext());
+        mRootView.addView(mContainer);
+        mRootView.addView(mState.mFakeWindowRootView);
+        setContentView(mRootView);
     }
 
-    public PlatformView detachView() {
-        mContainer.removeView(mView.getView());
-        return mView;
+    public PresentationState detachState() {
+        mContainer.removeAllViews();
+        mRootView.removeAllViews();
+        return mState;
     }
 
-    public View getView() {
-        if (mView == null)
+    public PlatformView getView() {
+        if (mState.mView == null)
             return null;
-        return mView.getView();
+        return mState.mView;
+    }
+
+    /*
+     * A view group that implements the same layout protocol that exist between the WindowManager and its direct
+     * children.
+     *
+     * Currently only a subset of the protocol is supported (gravity, x, and y).
+     */
+    static class FakeWindowViewGroup extends ViewGroup {
+        // Used in onLayout to keep the bounds of the current view.
+        // We keep it as a member to avoid object allocations during onLayout which are discouraged.
+        private final Rect mViewBounds;
+
+        // Used in onLayout to keep the bounds of the child views.
+        // We keep it as a member to avoid object allocations during onLayout which are discouraged.
+        private final Rect mChildRect;
+
+        public FakeWindowViewGroup(Context context) {
+            super(context);
+            mViewBounds = new Rect();
+            mChildRect = new Rect();
+        }
+
+        @Override
+        protected void onLayout(boolean changed, int l, int t, int r, int b) {
+            for(int i = 0; i < getChildCount(); i++) {
+                View child = getChildAt(i);
+                WindowManager.LayoutParams params = (WindowManager.LayoutParams) child.getLayoutParams();
+                mViewBounds.set(l, t, r, b);
+                Gravity.apply(params.gravity, child.getMeasuredWidth(), child.getMeasuredHeight(), mViewBounds, params.x,
+                        params.y, mChildRect);
+                child.layout(mChildRect.left, mChildRect.top, mChildRect.right, mChildRect.bottom);
+            }
+        }
+
+        @Override
+        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
+            for(int i = 0; i < getChildCount(); i++) {
+                View child = getChildAt(i);
+                child.measure(atMost(widthMeasureSpec), atMost(heightMeasureSpec));
+            }
+            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
+        }
+
+        private static int atMost(int measureSpec) {
+            return MeasureSpec.makeMeasureSpec(MeasureSpec.getSize(measureSpec), MeasureSpec.AT_MOST);
+        }
+    }
+
+    /**
+     * Proxies a Context replacing the WindowManager with our custom instance.
+     */
+    static class PresentationContext extends ContextWrapper {
+        private WindowManager mWindowManager;
+        private final WindowManagerHandler mWindowManagerHandler;
+
+        PresentationContext(Context base, WindowManagerHandler windowManagerHandler) {
+            super(base);
+            mWindowManagerHandler = windowManagerHandler;
+        }
+
+        @Override
+        public Object getSystemService(String name) {
+            if (WINDOW_SERVICE.equals(name)) {
+                return getWindowManager();
+            }
+            return super.getSystemService(name);
+        }
+
+        private WindowManager getWindowManager() {
+            if (mWindowManager == null) {
+                mWindowManager = mWindowManagerHandler.getWindowManager();
+            }
+            return mWindowManager;
+        }
+    }
+
+    /*
+     * A dynamic proxy handler for a WindowManager with custom overrides.
+     *
+     * The presentation's window manager delegates all calls to the default window manager.
+     * WindowManager#addView calls triggered by views that are attached to the virtual display are crashing
+     * (see: https://github.com/flutter/flutter/issues/20714). This was triggered when selecting text in an embedded
+     * WebView (as the selection handles are implemented as popup windows).
+     *
+     * This dynamic proxy overrides the addView, removeView, and updateViewLayout methods to prevent these crashes.
+     *
+     * This will be more efficient as a static proxy that's not using reflection, but as the engine is currently
+     * not being built against the latest Android SDK we cannot override all relevant method.
+     * Tracking issue for upgrading the engine's Android sdk: https://github.com/flutter/flutter/issues/20717
+     */
+    static class WindowManagerHandler implements InvocationHandler {
+        private static final String TAG = "PlatformViewsController";
+
+        private final WindowManager mDelegate;
+        FakeWindowViewGroup mFakeWindowRootView;
+
+        WindowManagerHandler(WindowManager delegate, FakeWindowViewGroup fakeWindowViewGroup) {
+            mDelegate = delegate;
+            mFakeWindowRootView = fakeWindowViewGroup;
+        }
+
+        public WindowManager getWindowManager() {
+            return (WindowManager) Proxy.newProxyInstance(
+                    WindowManager.class.getClassLoader(),
+                    new Class[] { WindowManager.class },
+                    this
+            );
+        }
+
+        @Override
+        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+            switch (method.getName()) {
+                case "addView":
+                    addView(args);
+                    return null;
+                case "removeView":
+                    removeView(args);
+                    return null;
+                case "updateViewLayout":
+                    updateViewLayout(args);
+                    return null;
+            }
+            try {
+                return method.invoke(mDelegate, args);
+            } catch (InvocationTargetException e) {
+                throw e.getCause();
+            }
+        }
+
+        private void addView(Object[] args) {
+            if (mFakeWindowRootView == null) {
+                Log.w(TAG, "Embedded view called addView while detached from presentation");
+                return;
+            }
+            View view = (View) args[0];
+            WindowManager.LayoutParams layoutParams = (WindowManager.LayoutParams) args[1];
+            mFakeWindowRootView.addView(view, layoutParams);
+        }
+
+        private void removeView(Object[] args) {
+            if (mFakeWindowRootView == null) {
+                Log.w(TAG, "Embedded view called removeView while detached from presentation");
+                return;
+            }
+            View view = (View) args[0];
+            mFakeWindowRootView.removeView(view);
+        }
+
+        private void updateViewLayout(Object[] args) {
+            if (mFakeWindowRootView == null) {
+                Log.w(TAG, "Embedded view called updateViewLayout while detached from presentation");
+                return;
+            }
+            View view = (View) args[0];
+            WindowManager.LayoutParams layoutParams = (WindowManager.LayoutParams) args[1];
+            mFakeWindowRootView.updateViewLayout(view, layoutParams);
+        }
     }
 }

shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java

@@ -72,7 +72,7 @@ private VirtualDisplayController(
     }
 
     public void resize(final int width, final int height, final Runnable onNewSizeFrameAvailable) {
-        final PlatformView view = mPresentation.detachView();
+        final SingleViewPresentation.PresentationState presentationState = mPresentation.detachState();
         // We detach the surface to prevent it being destroyed when releasing the vd.
         //
         // setSurface is only available starting API 20. We could support API 19 by re-creating a new
@@ -118,18 +118,21 @@ public void onDraw() {
             public void onViewDetachedFromWindow(View v) {}
         });
 
-        mPresentation = new SingleViewPresentation(mContext, mVirtualDisplay.getDisplay(), view);
+        mPresentation = new SingleViewPresentation(mContext, mVirtualDisplay.getDisplay(), presentationState);
         mPresentation.show();
     }
 
     public void dispose() {
-        mPresentation.detachView().dispose();
+        PlatformView view = mPresentation.getView();
+        mPresentation.detachState();
+        view.dispose();
         mVirtualDisplay.release();
     }
 
     public View getView() {
         if (mPresentation == null)
             return null;
-        return mPresentation.getView();
+        PlatformView platformView = mPresentation.getView();
+        return platformView.getView();
     }
 }