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sganovsganov
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Adding scroll actions to accessibility node info.
1. Scrolling actions are crucial for enabling a gesture based traversal of the UI and specifically scrollable containers especially lists and anything backed by an adapter. Since accessibility focus can land only attached views, it cannot visit views for adapter items not shown on the screen. Auto scrolling the list as a result of putting access focus ot a list item does not work well since the user may get trapped in a long list. Adding an accessibility node provider to emit virtual views for one view before the first and one after the last is complex and suffers the limitation of trapping the user. Accessibility service need an explicit scroll actions which may be performed upon an explicit user action. Hence, the user is informed for the start/end of the visible part of the list and he makes a deliberate choice to scroll. This will benefit also people developing Braille devices since they can scroll the content without telling the user to stop using the Braille controller and take the device out of his pocket to scroll and go back to the Braille controller. NOTE: Without these action large portions of the screen will be hard to access since users will have to touch and explore to find and scroll the list. Change-Id: Iafcf54d4967893205872b3649025a4e347a299ed
1 parent 1bc1b8a commit a1dc761

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+124
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‎api/current.txt‎

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Original file line numberDiff line numberDiff line change
@@ -25234,6 +25234,8 @@ package android.view.accessibility {
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field public static final int ACTION_NEXT_HTML_ELEMENT = 1024; // 0x400
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field public static final int ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY = 512; // 0x200
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field public static final int ACTION_PREVIOUS_HTML_ELEMENT = 2048; // 0x800
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field public static final int ACTION_SCROLL_BACKWARD = 8192; // 0x2000
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field public static final int ACTION_SCROLL_FORWARD = 4096; // 0x1000
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field public static final int ACTION_SELECT = 4; // 0x4
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field public static final android.os.Parcelable.Creator CREATOR;
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field public static final int FOCUS_ACCESSIBILITY = 2; // 0x2

‎core/java/android/view/accessibility/AccessibilityNodeInfo.java‎

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@@ -204,6 +204,16 @@ public class AccessibilityNodeInfo implements Parcelable {
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*/
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public static final int ACTION_PREVIOUS_HTML_ELEMENT = 0x00000800;
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/**
208+
* Action to scroll the node content forward.
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*/
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public static final int ACTION_SCROLL_FORWARD = 0x00001000;
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/**
213+
* Action to scroll the node content backward.
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*/
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public static final int ACTION_SCROLL_BACKWARD = 0x00002000;
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207217
/**
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* Argument for which movement granularity to be used when traversing the node text.
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* <p>
@@ -569,6 +579,16 @@ public void addChild(View root, int virtualDescendantId) {
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* @see AccessibilityNodeInfo#ACTION_CLEAR_FOCUS
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* @see AccessibilityNodeInfo#ACTION_SELECT
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* @see AccessibilityNodeInfo#ACTION_CLEAR_SELECTION
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* @see AccessibilityNodeInfo#ACTION_ACCESSIBILITY_FOCUS
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* @see AccessibilityNodeInfo#ACTION_CLEAR_ACCESSIBILITY_FOCUS
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* @see AccessibilityNodeInfo#ACTION_CLICK
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* @see AccessibilityNodeInfo#ACTION_LONG_CLICK
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* @see AccessibilityNodeInfo#ACTION_NEXT_AT_MOVEMENT_GRANULARITY
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* @see AccessibilityNodeInfo#ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY
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* @see AccessibilityNodeInfo#ACTION_NEXT_HTML_ELEMENT
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* @see AccessibilityNodeInfo#ACTION_PREVIOUS_HTML_ELEMENT
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* @see AccessibilityNodeInfo#ACTION_SCROLL_FORWARD
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* @see AccessibilityNodeInfo#ACTION_SCROLL_BACKWARD
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*/
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public int getActions() {
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return mActions;
@@ -1578,6 +1598,10 @@ private static String getActionSymbolicName(int action) {
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return "ACTION_NEXT_HTML_ELEMENT";
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case ACTION_PREVIOUS_HTML_ELEMENT:
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return "ACTION_PREVIOUS_HTML_ELEMENT";
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case ACTION_SCROLL_FORWARD:
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return "ACTION_SCROLL_FORWARD";
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case ACTION_SCROLL_BACKWARD:
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return "ACTION_SCROLL_BACKWARD";
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default:
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throw new IllegalArgumentException("Unknown action: " + action);
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}

‎core/java/android/widget/AbsListView.java‎

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Original file line numberDiff line numberDiff line change
@@ -1355,6 +1355,33 @@ public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
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public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
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super.onInitializeAccessibilityNodeInfo(info);
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info.setClassName(AbsListView.class.getName());
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if (getFirstVisiblePosition() > 0) {
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info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
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}
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if (getLastVisiblePosition() < getCount() - 1) {
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info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
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}
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}
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@Override
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public boolean performAccessibilityAction(int action, Bundle arguments) {
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switch (action) {
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case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
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if (getLastVisiblePosition() < getCount() - 1) {
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final int viewportHeight = getHeight() - mListPadding.top - mListPadding.bottom;
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smoothScrollBy(viewportHeight, PositionScroller.SCROLL_DURATION);
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return true;
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}
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} return false;
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case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
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if (mFirstPosition > 0) {
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final int viewportHeight = getHeight() - mListPadding.top - mListPadding.bottom;
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smoothScrollBy(-viewportHeight, PositionScroller.SCROLL_DURATION);
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return true;
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}
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} return false;
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}
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return super.performAccessibilityAction(action, arguments);
13581385
}
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13601387
/**

‎core/java/android/widget/HorizontalScrollView.java‎

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@@ -20,6 +20,7 @@
2020
import android.content.res.TypedArray;
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import android.graphics.Canvas;
2222
import android.graphics.Rect;
23+
import android.os.Bundle;
2324
import android.util.AttributeSet;
2425
import android.view.FocusFinder;
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import android.view.InputDevice;
@@ -736,11 +737,43 @@ protected void onOverScrolled(int scrollX, int scrollY,
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awakenScrollBars();
737738
}
738739

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@Override
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public boolean performAccessibilityAction(int action, Bundle arguments) {
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switch (action) {
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case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
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final int viewportWidth = getWidth() - mPaddingLeft - mPaddingRight;
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final int targetScrollX = Math.min(mScrollX + viewportWidth, getScrollRange());
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if (targetScrollX != mScrollX) {
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smoothScrollTo(targetScrollX, 0);
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return true;
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}
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} return false;
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case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
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final int viewportWidth = getWidth() - mPaddingLeft - mPaddingRight;
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final int targetScrollX = Math.max(0, mScrollX - viewportWidth);
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if (targetScrollX != mScrollX) {
755+
smoothScrollTo(targetScrollX, 0);
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return true;
757+
}
758+
} return false;
759+
}
760+
return super.performAccessibilityAction(action, arguments);
761+
}
762+
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@Override
740764
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
741765
super.onInitializeAccessibilityNodeInfo(info);
742766
info.setClassName(HorizontalScrollView.class.getName());
743-
info.setScrollable(getScrollRange() > 0);
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final int scrollRange = getScrollRange();
768+
if (scrollRange > 0) {
769+
info.setScrollable(true);
770+
if (mScrollX > 0) {
771+
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
772+
}
773+
if (mScrollX < scrollRange) {
774+
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
775+
}
776+
}
744777
}
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746779
@Override

‎core/java/android/widget/ScrollView.java‎

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Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
2222
import android.content.res.TypedArray;
2323
import android.graphics.Canvas;
2424
import android.graphics.Rect;
25+
import android.os.Bundle;
2526
import android.os.StrictMode;
2627
import android.util.AttributeSet;
2728
import android.view.FocusFinder;
@@ -739,11 +740,43 @@ protected void onOverScrolled(int scrollX, int scrollY,
739740
awakenScrollBars();
740741
}
741742

743+
@Override
744+
public boolean performAccessibilityAction(int action, Bundle arguments) {
745+
switch (action) {
746+
case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
747+
final int viewportHeight = getHeight() - mPaddingBottom - mPaddingTop;
748+
final int targetScrollY = Math.min(mScrollY + viewportHeight, getScrollRange());
749+
if (targetScrollY != mScrollY) {
750+
smoothScrollTo(0, targetScrollY);
751+
return true;
752+
}
753+
} return false;
754+
case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
755+
final int viewportHeight = getHeight() - mPaddingBottom - mPaddingTop;
756+
final int targetScrollY = Math.max(mScrollY - viewportHeight, 0);
757+
if (targetScrollY != mScrollY) {
758+
smoothScrollTo(0, targetScrollY);
759+
return true;
760+
}
761+
} return false;
762+
}
763+
return super.performAccessibilityAction(action, arguments);
764+
}
765+
742766
@Override
743767
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
744768
super.onInitializeAccessibilityNodeInfo(info);
745769
info.setClassName(ScrollView.class.getName());
746-
info.setScrollable(getScrollRange() > 0);
770+
final int scrollRange = getScrollRange();
771+
if (scrollRange > 0) {
772+
info.setScrollable(true);
773+
if (mScrollY > 0) {
774+
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
775+
}
776+
if (mScrollY < scrollRange) {
777+
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
778+
}
779+
}
747780
}
748781

749782
@Override

‎services/java/com/android/server/accessibility/AccessibilityManagerService.java‎

Lines changed: 3 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1701,14 +1701,9 @@ final class SecurityPolicy {
17011701
| AccessibilityNodeInfo.ACTION_NEXT_AT_MOVEMENT_GRANULARITY
17021702
| AccessibilityNodeInfo.ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY
17031703
| AccessibilityNodeInfo.ACTION_NEXT_HTML_ELEMENT
1704-
| AccessibilityNodeInfo.ACTION_PREVIOUS_HTML_ELEMENT;
1705-
1706-
private static final int VALID_GRANULARITIES =
1707-
AccessibilityNodeInfo.MOVEMENT_GRANULARITY_CHARACTER
1708-
| AccessibilityNodeInfo.MOVEMENT_GRANULARITY_WORD
1709-
| AccessibilityNodeInfo.MOVEMENT_GRANULARITY_LINE
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| AccessibilityNodeInfo.MOVEMENT_GRANULARITY_PARAGRAPH
1711-
| AccessibilityNodeInfo.MOVEMENT_GRANULARITY_PAGE;
1704+
| AccessibilityNodeInfo.ACTION_PREVIOUS_HTML_ELEMENT
1705+
| AccessibilityNodeInfo.ACTION_SCROLL_FORWARD
1706+
| AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD;
17121707

17131708
private static final int RETRIEVAL_ALLOWING_EVENT_TYPES =
17141709
AccessibilityEvent.TYPE_VIEW_CLICKED

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