Delegate a11y events and action to/from embedded Android platform vie…

…ws. (flutter#8250)

Delegate a11y events and action to/from embedded Android platfrom views.

This handles delegation of:
  * AccessibilityNodeProvider#performAction
  * ViewGroup#requestSendAccessibilityEvent
  * View#onHoverEvent

Additionally updates the currently input accessibility focused node state that is
tracked by the a11y bridge when an embedded view's node is focused.

ci/licenses_golden/licenses_flutter

@@ -511,6 +511,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/common/StandardM
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/common/StringCodec.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/editing/InputConnectionAdaptor.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/AccessibilityEventsDelegate.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformView.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java

shell/platform/android/BUILD.gn

@@ -153,6 +153,7 @@ java_library("flutter_shell_java") {
     "io/flutter/plugin/common/StringCodec.java",
     "io/flutter/plugin/editing/InputConnectionAdaptor.java",
     "io/flutter/plugin/editing/TextInputPlugin.java",
+    "io/flutter/plugin/platform/AccessibilityEventsDelegate.java",
     "io/flutter/plugin/platform/PlatformPlugin.java",
     "io/flutter/plugin/platform/PlatformView.java",
     "io/flutter/plugin/platform/PlatformViewFactory.java",

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

@@ -0,0 +1,49 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugin.platform;
+
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+import android.view.View;
+import android.view.accessibility.AccessibilityEvent;
+import io.flutter.view.AccessibilityBridge;
+
+/**
+ * Delegates accessibility events to the currently attached accessibility bridge if one is attached.
+ */
+class AccessibilityEventsDelegate {
+    private AccessibilityBridge accessibilityBridge;
+
+    /**
+     * Delegates handling of {@link android.view.ViewParent#requestSendAccessibilityEvent} to the accessibility bridge.
+     *
+     * This is a no-op if there is no accessibility delegate set.
+     *
+     * This is used by embedded platform views to propagate accessibility events from their view hierarchy to the
+     * accessibility bridge.
+     *
+     * As the embedded view doesn't have to be the only View in the embedded hierarchy (it can have child views) and the
+     * event might have been originated from any view in this hierarchy, this method gets both a reference to the
+     * embedded platform view, and a reference to the view from its hierarchy that sent the event.
+     *
+     * @param embeddedView the embedded platform view for which the event is delegated
+     * @param eventOrigin the view in the embedded view's hierarchy that sent the event.
+     * @return True if the event was sent.
+     */
+    public boolean requestSendAccessibilityEvent(@NonNull View embeddedView, @NonNull View eventOrigin, @NonNull AccessibilityEvent event) {
+        if (accessibilityBridge == null) {
+            return false;
+        }
+        return accessibilityBridge.externalViewRequestSendAccessibilityEvent(embeddedView, eventOrigin, event);
+    }
+
+    /*
+     * This setter should only be used directly in PlatformViewsController when attached/detached to an accessibility
+     * bridge.
+     */
+    void setAccessibilityBridge(@Nullable AccessibilityBridge accessibilityBridge) {
+        this.accessibilityBridge = accessibilityBridge;
+    }
+}

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

@@ -52,13 +52,14 @@ public class PlatformViewsController implements MethodChannel.MethodCallHandler,
     private BinaryMessenger mMessenger;
 
     // The accessibility bridge to which accessibility events form the platform views will be dispatched.
-    private AccessibilityBridge accessibilityBridge;
+    private final AccessibilityEventsDelegate mAccessibilityEventsDelegate;
 
     private final HashMap<Integer, VirtualDisplayController> vdControllers;
 
     public PlatformViewsController() {
         mRegistry = new PlatformViewRegistryImpl();
         vdControllers = new HashMap<>();
+        mAccessibilityEventsDelegate = new AccessibilityEventsDelegate();
     }
 
     /**
@@ -100,12 +101,12 @@ public void detach() {
 
     @Override
     public void attachAccessibilityBridge(AccessibilityBridge accessibilityBridge) {
-        this.accessibilityBridge = accessibilityBridge;
+        mAccessibilityEventsDelegate.setAccessibilityBridge(accessibilityBridge);
     }
 
     @Override
     public void detachAccessibiltyBridge() {
-        this.accessibilityBridge = null;
+        mAccessibilityEventsDelegate.setAccessibilityBridge(null);
     }
 
     public PlatformViewRegistry getRegistry() {
@@ -201,6 +202,7 @@ private void createPlatformView(MethodCall call, MethodChannel.Result result) {
         TextureRegistry.SurfaceTextureEntry textureEntry = mTextureRegistry.createSurfaceTexture();
         VirtualDisplayController vdController = VirtualDisplayController.create(
                 mContext,
+                mAccessibilityEventsDelegate,
                 viewFactory,
                 textureEntry,
                 toPhysicalPixels(logicalWidth),

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

@@ -13,6 +13,7 @@
 import android.os.Bundle;
 import android.util.Log;
 import android.view.*;
+import android.view.accessibility.AccessibilityEvent;
 import android.widget.FrameLayout;
 
 import java.lang.reflect.*;
@@ -57,6 +58,9 @@ static class PresentationState {
 
     private final PlatformViewFactory mViewFactory;
 
+    // A reference to the current accessibility bridge to which accessibility events will be delegated.
+    private final AccessibilityEventsDelegate mAccessibilityEventsDelegate;
+
     // This is the view id assigned by the Flutter framework to the embedded view, we keep it here
     // so when we create the platform view we can tell it its view id.
     private int mViewId;
@@ -67,7 +71,7 @@ static class PresentationState {
 
     // 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;
+    private AccessibilityDelegatingFrameLayout mRootView;
 
     // Contains the embedded platform view (mView.getView()) when it is attached to the presentation.
     private FrameLayout mContainer;
@@ -82,10 +86,13 @@ public SingleViewPresentation(
             Context outerContext,
             Display display,
             PlatformViewFactory viewFactory,
+            AccessibilityEventsDelegate accessibilityEventsDelegate,
             int viewId,
-            Object createParams) {
+            Object createParams
+    ) {
         super(outerContext, display);
         mViewFactory = viewFactory;
+        mAccessibilityEventsDelegate = accessibilityEventsDelegate;
         mViewId = viewId;
         mCreateParams = createParams;
         mState = new PresentationState();
@@ -102,8 +109,14 @@ public SingleViewPresentation(
      * <p>The display's density must match the density of the context used
      * when the view was created.
      */
-    public SingleViewPresentation(Context outerContext, Display display, PresentationState state) {
+    public SingleViewPresentation(
+            Context outerContext,
+            Display display,
+            AccessibilityEventsDelegate accessibilityEventsDelegate,
+            PresentationState state
+    ) {
         super(outerContext, display);
+        mAccessibilityEventsDelegate = accessibilityEventsDelegate;
         mViewFactory = null;
         mState = state;
         getWindow().setFlags(
@@ -130,8 +143,9 @@ protected void onCreate(Bundle savedInstanceState) {
             mState.mView = mViewFactory.create(context, mViewId, mCreateParams);
         }
 
-        mContainer.addView(mState.mView.getView());
-        mRootView = new FrameLayout(getContext());
+        View embeddedView = mState.mView.getView();
+        mContainer.addView(embeddedView);
+        mRootView = new AccessibilityDelegatingFrameLayout(getContext(), mAccessibilityEventsDelegate, embeddedView);
         mRootView.addView(mContainer);
         mRootView.addView(mState.mFakeWindowRootView);
         setContentView(mRootView);
@@ -320,4 +334,24 @@ private void updateViewLayout(Object[] args) {
             mFakeWindowRootView.updateViewLayout(view, layoutParams);
         }
     }
+
+    private static class AccessibilityDelegatingFrameLayout extends FrameLayout {
+        private final AccessibilityEventsDelegate mAccessibilityEventsDelegate;
+        private final View mEmbeddedView;
+
+        public AccessibilityDelegatingFrameLayout(
+                Context context,
+                AccessibilityEventsDelegate accessibilityEventsDelegate,
+                View ebeddedView
+        ) {
+            super(context);
+            mAccessibilityEventsDelegate = accessibilityEventsDelegate;
+            mEmbeddedView = ebeddedView;
+        }
+
+        @Override
+        public boolean requestSendAccessibilityEvent(View child, AccessibilityEvent event) {
+            return mAccessibilityEventsDelegate.requestSendAccessibilityEvent(mEmbeddedView, child, event);
+        }
+    }
 }

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

@@ -19,6 +19,7 @@ class VirtualDisplayController {
 
     public static VirtualDisplayController create(
             Context context,
+            AccessibilityEventsDelegate accessibilityEventsDelegate,
             PlatformViewFactory viewFactory,
             TextureRegistry.SurfaceTextureEntry textureEntry,
             int width,
@@ -45,10 +46,11 @@ public static VirtualDisplayController create(
         }
 
         return new VirtualDisplayController(
-                context, virtualDisplay, viewFactory, surface, textureEntry, viewId, createParams);
+                context, accessibilityEventsDelegate, virtualDisplay, viewFactory, surface, textureEntry, viewId, createParams);
     }
 
     private final Context mContext;
+    private final AccessibilityEventsDelegate mAccessibilityEventsDelegate;
     private final int mDensityDpi;
     private final TextureRegistry.SurfaceTextureEntry mTextureEntry;
     private VirtualDisplay mVirtualDisplay;
@@ -58,20 +60,22 @@ public static VirtualDisplayController create(
 
     private VirtualDisplayController(
             Context context,
+            AccessibilityEventsDelegate accessibilityEventsDelegate,
             VirtualDisplay virtualDisplay,
             PlatformViewFactory viewFactory,
             Surface surface,
             TextureRegistry.SurfaceTextureEntry textureEntry,
             int viewId,
             Object createParams
     ) {
+        mContext = context;
+        mAccessibilityEventsDelegate = accessibilityEventsDelegate;
         mTextureEntry = textureEntry;
         mSurface = surface;
-        mContext = context;
         mVirtualDisplay = virtualDisplay;
         mDensityDpi = context.getResources().getDisplayMetrics().densityDpi;
         mPresentation = new SingleViewPresentation(
-                context, mVirtualDisplay.getDisplay(), viewFactory, viewId, createParams);
+                context, mVirtualDisplay.getDisplay(), viewFactory, accessibilityEventsDelegate, viewId, createParams);
         mPresentation.show();
     }
 
@@ -121,7 +125,7 @@ public void run() {
             public void onViewDetachedFromWindow(View v) {}
         });
 
-        mPresentation = new SingleViewPresentation(mContext, mVirtualDisplay.getDisplay(), presentationState);
+        mPresentation = new SingleViewPresentation(mContext, mVirtualDisplay.getDisplay(), mAccessibilityEventsDelegate, presentationState);
         mPresentation.show();
     }
 

shell/platform/android/io/flutter/view/AccessibilityBridge.java

@@ -5,9 +5,7 @@
 package io.flutter.view;
 
 import android.annotation.TargetApi;
-import android.app.Activity;
 import android.content.ContentResolver;
-import android.content.Context;
 import android.database.ContentObserver;
 import android.graphics.Rect;
 import android.net.Uri;
@@ -23,7 +21,6 @@
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.WindowInsets;
-import android.view.WindowManager;
 import android.view.accessibility.AccessibilityEvent;
 import android.view.accessibility.AccessibilityManager;
 import android.view.accessibility.AccessibilityNodeInfo;
@@ -158,9 +155,23 @@ public class AccessibilityBridge extends AccessibilityNodeProvider {
 
     // The {@code SemanticsNode} within Flutter that currently has the focus of Android's
     // accessibility system.
+    //
+    // This is null when a node embedded by the AccessibilityViewEmbedder has the focus.
     @Nullable
     private SemanticsNode accessibilityFocusedSemanticsNode;
 
+    // The virtual ID of the currently embedded node with accessibility focus.
+    //
+    // This is the ID of a node generated by the AccessibilityViewEmbedder if an embedded node is focused,
+    // null otherwise.
+    private Integer embeddedAccessibilityFocusedNodeId;
+
+    // The virtual ID of the currently embedded node with input focus.
+    //
+    // This is the ID of a node generated by the AccessibilityViewEmbedder if an embedded node is focused,
+    // null otherwise.
+    private Integer embeddedInputFocusedNodeId;
+
     // The accessibility features that should currently be active within Flutter, represented as
     // a bitmask whose values comes from {@link AccessibilityFeature}.
     private int accessibilityFeatureFlags = 0;
@@ -762,6 +773,14 @@ public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
      */
     @Override
     public boolean performAction(int virtualViewId, int accessibilityAction, @Nullable Bundle arguments) {
+        if (virtualViewId >= MIN_ENGINE_GENERATED_NODE_ID) {
+            // The node is in the engine generated range, and is handled by the accessibility view embedder.
+            boolean didPerform = accessibilityViewEmbedder.performAction(virtualViewId, accessibilityAction, arguments);
+            if (didPerform && accessibilityAction == AccessibilityNodeInfo.ACTION_CLEAR_ACCESSIBILITY_FOCUS) {
+                embeddedAccessibilityFocusedNodeId = null;
+            }
+            return didPerform;
+        }
         SemanticsNode semanticsNode = flutterSemanticsTree.get(virtualViewId);
         if (semanticsNode == null) {
             return false;
@@ -841,6 +860,7 @@ public boolean performAction(int virtualViewId, int accessibilityAction, @Nullab
                     AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUS_CLEARED
                 );
                 accessibilityFocusedSemanticsNode = null;
+                embeddedAccessibilityFocusedNodeId = null;
                 return true;
             }
             case AccessibilityNodeInfo.ACTION_ACCESSIBILITY_FOCUS: {
@@ -1014,12 +1034,18 @@ public AccessibilityNodeInfo findFocus(int focus) {
                 if (inputFocusedSemanticsNode != null) {
                     return createAccessibilityNodeInfo(inputFocusedSemanticsNode.id);
                 }
+                if (embeddedInputFocusedNodeId != null) {
+                    return createAccessibilityNodeInfo(embeddedInputFocusedNodeId);
+                }
             }
             // Fall through to check FOCUS_ACCESSIBILITY
             case AccessibilityNodeInfo.FOCUS_ACCESSIBILITY: {
                 if (accessibilityFocusedSemanticsNode != null) {
                     return createAccessibilityNodeInfo(accessibilityFocusedSemanticsNode.id);
                 }
+                if (embeddedAccessibilityFocusedNodeId != null) {
+                    return createAccessibilityNodeInfo(embeddedAccessibilityFocusedNodeId);
+                }
             }
         }
         return null;
@@ -1090,6 +1116,11 @@ public boolean onAccessibilityHoverEvent(MotionEvent event) {
             return false;
         }
 
+        SemanticsNode semanticsNodeUnderCursor = getRootSemanticsNode().hitTest(new float[] {event.getX(), event.getY(), 0, 1});
+        if (semanticsNodeUnderCursor.platformViewId != -1) {
+            return accessibilityViewEmbedder.onAccessibilityHoverEvent(semanticsNodeUnderCursor.id, event);
+        }
+
         if (event.getAction() == MotionEvent.ACTION_HOVER_ENTER || event.getAction() == MotionEvent.ACTION_HOVER_MOVE) {
             handleTouchExploration(event.getX(), event.getY());
         } else if (event.getAction() == MotionEvent.ACTION_HOVER_EXIT) {
@@ -2061,4 +2092,46 @@ private String getValueLabelHint() {
             return sb.length() > 0 ? sb.toString() : null;
         }
     }
+
+    /**
+     * Delegates handling of {@link android.view.ViewParent#requestSendAccessibilityEvent} to the accessibility bridge.
+     *
+     * This is used by embedded platform views to propagate accessibility events from their view hierarchy to the
+     * accessibility bridge.
+     *
+     * As the embedded view doesn't have to be the only View in the embedded hierarchy (it can have child views) and the
+     * event might have been originated from any view in this hierarchy, this method gets both a reference to the
+     * embedded platform view, and a reference to the view from its hierarchy that sent the event.
+     *
+     * @param embeddedView the embedded platform view for which the event is delegated
+     * @param eventOrigin the view in the embedded view's hierarchy that sent the event.
+     * @return True if the event was sent.
+     */
+    public boolean externalViewRequestSendAccessibilityEvent(View embeddedView, View eventOrigin, AccessibilityEvent event) {
+        if (!accessibilityViewEmbedder.requestSendAccessibilityEvent(embeddedView, eventOrigin, event)){
+            return false;
+        }
+        Integer virtualNodeId = accessibilityViewEmbedder.getRecordFlutterId(embeddedView, event);
+        if (virtualNodeId == null) {
+            return false;
+        }
+        switch(event.getEventType()) {
+            case  AccessibilityEvent.TYPE_VIEW_HOVER_ENTER:
+                hoveredObject = null;
+                break;
+            case AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUSED:
+                embeddedAccessibilityFocusedNodeId = virtualNodeId;
+                accessibilityFocusedSemanticsNode = null;
+                break;
+            case AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUS_CLEARED:
+                embeddedInputFocusedNodeId = null;
+                embeddedAccessibilityFocusedNodeId = null;
+                break;
+            case AccessibilityEvent.TYPE_VIEW_FOCUSED:
+                embeddedInputFocusedNodeId = virtualNodeId;
+                inputFocusedSemanticsNode = null;
+                break;
+        }
+        return true;
+    }
 }