Announce in/out of list (flutter#6918)

* Support in/out of list announcements on Android

ci/licenses_golden/licenses_flutter

@@ -450,6 +450,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SingleV
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/PathUtils.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/Preconditions.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/util/Predicate.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/view/AccessibilityBridge.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/view/FlutterCallbackInformation.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/view/FlutterMain.java

shell/platform/android/BUILD.gn

@@ -136,6 +136,7 @@ java_library("flutter_shell_java") {
     "io/flutter/plugin/platform/VirtualDisplayController.java",
     "io/flutter/util/PathUtils.java",
     "io/flutter/util/Preconditions.java",
+    "io/flutter/util/Predicate.java",
     "io/flutter/view/AccessibilityBridge.java",
     "io/flutter/view/FlutterCallbackInformation.java",
     "io/flutter/view/FlutterMain.java",

shell/platform/android/io/flutter/util/Predicate.java

@@ -0,0 +1,11 @@
+// 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.util;
+
+// TODO(dnfield): remove this if/when we can use appcompat to support it.
+// java.util.function.Predicate isn't available until API24
+public interface Predicate<T> {
+    public abstract boolean test(T t);
+}

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

@@ -16,6 +16,7 @@
 import android.view.accessibility.AccessibilityNodeProvider;
 import io.flutter.plugin.common.BasicMessageChannel;
 import io.flutter.plugin.common.StandardMessageCodec;
+import io.flutter.util.Predicate;
 
 import java.nio.ByteBuffer;
 import java.util.*;
@@ -125,6 +126,21 @@ void setAccessibilityEnabled(boolean accessibilityEnabled) {
         }
     }
 
+    private boolean shouldSetCollectionInfo(final SemanticsObject object) {
+        // TalkBack expects a number of rows and/or columns greater than 0 to announce
+        // in list and out of list.  For an infinite or growing list, you have to
+        // specify something > 0 to get "in list" announcements.
+        // TalkBack will also only track one list at a time, so we only want to set this
+        // for a list that contains the current a11y focused object - otherwise, if there
+        // are two lists or nested lists, we may end up with announcements for only the last
+        // one that is currently available in the semantics tree.  However, we also want
+        // to set it if we're exiting a list to a non-list, so that we can get the "out of list"
+        // announcement when A11y focus moves out of a list and not into another list.
+        return object.scrollChildren > 0
+                && (hasSemanticsObjectAncestor(mA11yFocusedObject, o -> o == object)
+                    || !hasSemanticsObjectAncestor(mA11yFocusedObject, o -> o.hasFlag(Flag.HAS_IMPLICIT_SCROLLING)));
+    }
+
     @Override
     @SuppressWarnings("deprecation")
     public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
@@ -266,14 +282,35 @@ public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
         if (object.hasAction(Action.SCROLL_LEFT) || object.hasAction(Action.SCROLL_UP)
                 || object.hasAction(Action.SCROLL_RIGHT) || object.hasAction(Action.SCROLL_DOWN)) {
             result.setScrollable(true);
+
             // This tells Android's a11y to send scroll events when reaching the end of
             // the visible viewport of a scrollable, unless the node itself does not
             // allow implicit scrolling - then we leave the className as view.View.
+            //
+            // We should prefer setCollectionInfo to the class names, as this way we get "In List"
+            // and "Out of list" announcements.  But we don't always know the counts, so we
+            // can fallback to the generic scroll view class names.
+            // TODO(dnfield): We should add semantics properties for rows and columns in 2 dimensional lists, e.g.
+            // GridView.  Right now, we're only supporting ListViews and only if they have scroll children.
             if (object.hasFlag(Flag.HAS_IMPLICIT_SCROLLING)) {
                 if (object.hasAction(Action.SCROLL_LEFT) || object.hasAction(Action.SCROLL_RIGHT)) {
-                    result.setClassName("android.widget.HorizontalScrollView");
+                    if (shouldSetCollectionInfo(object)) {
+                        result.setCollectionInfo(AccessibilityNodeInfo.CollectionInfo.obtain(
+                            0, // rows
+                            object.scrollChildren, // columns
+                            false)); // hierarchical
+                    } else {
+                        result.setClassName("android.widget.HorizontalScrollView");
+                    }
                 } else {
-                    result.setClassName("android.widget.ScrollView");
+                    if (shouldSetCollectionInfo(object)) {
+                        result.setCollectionInfo(AccessibilityNodeInfo.CollectionInfo.obtain(
+                            object.scrollChildren, // rows
+                            0, // columns
+                            false)); // hierarchical
+                    } else {
+                        result.setClassName("android.widget.ScrollView");
+                    }
                 }
             }
             // TODO(ianh): Once we're on SDK v23+, call addAction to
@@ -960,6 +997,11 @@ boolean isStandardAction() {
     /// Value is derived from ACTION_TYPE_MASK in AccessibilityNodeInfo.java
     static int firstResourceId = 267386881;
 
+
+    static boolean hasSemanticsObjectAncestor(SemanticsObject target, Predicate<SemanticsObject> tester) {
+        return target != null && target.getAncestor(tester) != null;
+    }
+
     private class SemanticsObject {
         SemanticsObject() {}
 
@@ -1012,6 +1054,17 @@ private class SemanticsObject {
         private float[] globalTransform;
         private Rect globalRect;
 
+        SemanticsObject getAncestor(Predicate<SemanticsObject> tester) {
+            SemanticsObject nextAncestor = parent;
+            while (nextAncestor != null) {
+                if (tester.test(nextAncestor)) {
+                    return nextAncestor;
+                }
+                nextAncestor = nextAncestor.parent;
+            }
+            return null;
+        }
+
         boolean hasAction(Action action) {
             return (actions & action.value) != 0;
         }