This guide steps through a sample showcasing some best practices to support accessibility with custom views in an Android TV app. The guide shows how to create a simple activity that uses the Canvas API to draw four images that are focusable and let accessibility services navigate between them.
Create layout XML file
Create a layout file for the custom view activity.
<?xml version="1.0" encoding="utf-8">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".custom.CustomViewActivity">
<com.example.tvcustomviews.SampleCustomView
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>
The following sections define the
com.example.tvcustomviews.SampleCustomView class.
Define a simple activity
Create a simple activity to load the layout XML file.
Kotlin
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
class CustomViewBestPracticeActivity:AppCompatActivity() {
protected fun onCreate(savedInstanceState:Bundle) {
super.onCreate(savedInstanceState)
setContentView(R.layout.custom_view_best_practices)
}
}
Java
package com.example.tvcustomviews;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
public class CustomViewBestPracticeActivity extends AppCompatActivity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.custom_view_best_practices);
}
}
Define the SampleCustomView class
Next, define the class and draw four images using a canvas.
Kotlin
package com.example.tvcustomviews
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.graphics.Rect
import android.util.AttributeSet
import android.view.View
import androidx.annotation.Nullable
import androidx.core.view.ViewCompat
import java.util.HashMap
class SampleCustomView:View {
internal val virtualIdRectMap:Map<Int, VirtualRect> = HashMap<Int, VirtualRect>()
private val rectangleId = 1
internal class VirtualRect(rect:Rect, paint:Paint, id:Int) {
val rect:Rect
val paint:Paint
val id:Int = 0
init{
this.rect = rect
this.paint = paint
this.id = id
}
}
constructor(context:Context) : super(context) {
init()
}
constructor(context:Context, @Nullable attrs:AttributeSet) : super(context, attrs) {
init()
}
constructor(context:Context, @Nullable attrs:AttributeSet, defStyleAttr:Int) : super(context, attrs, defStyleAttr) {
init()
}
private fun init() {
setRectangle()
ViewCompat.setAccessibilityDelegate(this,
SampleExploreByTouchHelper(this))
}
protected fun onDraw(canvas:Canvas) {
super.onDraw(canvas)
for (mapElement in virtualIdRectMap.entries)
{
val virtualRect = mapElement.value
canvas.drawRect(virtualRect.rect, virtualRect.paint)
}
}
private fun setRectangle() {
val paint = Paint(Paint.ANTI_ALIAS_FLAG)
paint.setColor(RECTANGLE_COLOR)
val leftTopRectangle = Rect()
leftTopRectangle.left = RECTANGLE_START_POINT_LEFT
leftTopRectangle.right = leftTopRectangle.left + RECTANGLE_WIDTH
leftTopRectangle.top = RECTANGLE_START_POINT_TOP
leftTopRectangle.bottom = leftTopRectangle.top + RECTANGLE_HEIGHT
virtualIdRectMap.put(rectangleId, VirtualRect(leftTopRectangle, paint, rectangleId++))
val rightTopRectangle = Rect()
rightTopRectangle.left = leftTopRectangle.right + HORIZONTAL_PADDING
rightTopRectangle.right = rightTopRectangle.left + RECTANGLE_WIDTH
rightTopRectangle.top = leftTopRectangle.top
rightTopRectangle.bottom = rightTopRectangle.top + RECTANGLE_HEIGHT
virtualIdRectMap.put(rectangleId, VirtualRect(rightTopRectangle, paint, rectangleId++))
val leftBottomRectangle = Rect()
leftBottomRectangle.left = leftTopRectangle.left
leftBottomRectangle.right = leftBottomRectangle.left + RECTANGLE_WIDTH
leftBottomRectangle.top = leftTopRectangle.bottom + VERTICAL_PADDING
leftBottomRectangle.bottom = leftBottomRectangle.top + RECTANGLE_HEIGHT
virtualIdRectMap.put(rectangleId, VirtualRect(leftBottomRectangle, paint, rectangleId++))
val rightBottomRectangle = Rect()
rightBottomRectangle.left = leftBottomRectangle.right + HORIZONTAL_PADDING
rightBottomRectangle.right = rightBottomRectangle.left + RECTANGLE_WIDTH
rightBottomRectangle.top = leftBottomRectangle.top
rightBottomRectangle.bottom = rightBottomRectangle.top + RECTANGLE_HEIGHT
virtualIdRectMap.put(rectangleId, VirtualRect(rightBottomRectangle, paint, rectangleId++))
}
companion object {
private val RECTANGLE_START_POINT_LEFT = 50
private val RECTANGLE_START_POINT_TOP = 100
private val RECTANGLE_WIDTH = 200
private val RECTANGLE_HEIGHT = 100
private val HORIZONTAL_PADDING = 50
private val VERTICAL_PADDING = 100
private val RECTANGLE_COLOR = Color.argb(100, 0, 163, 245)
}
}
Java
package com.example.tvcustomviews;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;
import androidx.annotation.Nullable;
import androidx.core.view.ViewCompat;
import java.util.HashMap;
import java.util.Map;
public class SampleCustomView extends View {
final Map<Integer, VirtualRect> virtualIdRectMap = new HashMap<>();
private static final int RECTANGLE_START_POINT_LEFT = 50;
private static final int RECTANGLE_START_POINT_TOP = 100;
private static final int RECTANGLE_WIDTH = 200;
private static final int RECTANGLE_HEIGHT = 100;
private static final int HORIZONTAL_PADDING = 50;
private static final int VERTICAL_PADDING = 100;
private static final int RECTANGLE_COLOR = Color.argb(100, 0, 163, 245);
private int rectangleId = 1;
static class VirtualRect {
final Rect rect;
final Paint paint;
final int id;
VirtualRect(Rect rect, Paint paint, int id) {
this.rect = rect;
this.paint = paint;
this.id = id;
}
}
public SampleCustomView(Context context) {
super(context);
init();
}
public SampleCustomView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
init();
}
public SampleCustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
setRectangle();
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (Map.Entry<Integer, VirtualRect> mapElement :
virtualIdRectMap.entrySet()) {
VirtualRect virtualRect = mapElement.getValue();
canvas.drawRect(virtualRect.rect, virtualRect.paint);
}
}
private void setRectangle() {
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(RECTANGLE_COLOR);
Rect leftTopRectangle = new Rect();
leftTopRectangle.left = RECTANGLE_START_POINT_LEFT;
leftTopRectangle.right = leftTopRectangle.left + RECTANGLE_WIDTH;
leftTopRectangle.top = RECTANGLE_START_POINT_TOP;
leftTopRectangle.bottom = leftTopRectangle.top + RECTANGLE_HEIGHT;
virtualIdRectMap.put(rectangleId, new VirtualRect(leftTopRectangle, paint, rectangleId++));
Rect rightTopRectangle = new Rect();
rightTopRectangle.left = leftTopRectangle.right + HORIZONTAL_PADDING;
rightTopRectangle.right = rightTopRectangle.left + RECTANGLE_WIDTH;
rightTopRectangle.top = leftTopRectangle.top;
rightTopRectangle.bottom = rightTopRectangle.top + RECTANGLE_HEIGHT;
virtualIdRectMap.put(rectangleId, new VirtualRect(rightTopRectangle, paint, rectangleId++));
Rect leftBottomRectangle = new Rect();
leftBottomRectangle.left = leftTopRectangle.left;
leftBottomRectangle.right = leftBottomRectangle.left + RECTANGLE_WIDTH;
leftBottomRectangle.top = leftTopRectangle.bottom + VERTICAL_PADDING;
leftBottomRectangle.bottom = leftBottomRectangle.top + RECTANGLE_HEIGHT;
virtualIdRectMap.put(rectangleId, new VirtualRect(leftBottomRectangle, paint, rectangleId++));
Rect rightBottomRectangle = new Rect();
rightBottomRectangle.left = leftBottomRectangle.right + HORIZONTAL_PADDING;
rightBottomRectangle.right = rightBottomRectangle.left + RECTANGLE_WIDTH;
rightBottomRectangle.top = leftBottomRectangle.top;
rightBottomRectangle.bottom = rightBottomRectangle.top + RECTANGLE_HEIGHT;
virtualIdRectMap.put(rectangleId, new VirtualRect(rightBottomRectangle, paint, rectangleId++));
}
}
The application in this state displays four blue rectangles on screen when it runs. But when Talkback is switched on, you can't navigate to the rectangles. In other words, these rectangles can't have accessibility focus.
Define ExploreByTouchHelper to expose AccessiblityNodeInfo
Define SampleExploreByTouchHelper by inheriting ExploreByTouchHelper and
implementing its methods.
Kotlin
package com.example.tvcustomviews
import android.graphics.Rect
import android.os.Bundle
import android.util.Log
import android.widget.ImageView
import androidx.annotation.NonNull
import androidx.annotation.Nullable
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat.AccessibilityActionCompat
import androidx.customview.widget.ExploreByTouchHelper
import com.example.tvcustomviews.SampleCustomView.VirtualRect
import java.util.Objects
internal class SampleExploreByTouchHelper(parentView:SampleCustomView):ExploreByTouchHelper(parentView) {
private val TAG = SampleExploreByTouchHelper::class.java!!.getName()
private val parentView:SampleCustomView
init{
this.parentView = parentView
}
/**
* Define AccessibilityNodeInfo objects with necessary attributes.
* Set required attributes into the AccessibilityNodeInfo for the UI
* component whose virtualID is the virtualViewId.
* @param virtualViewId: virtual ID for the component.
* @param node: the AccessibilityNodeInfoCompat used to set the attribute.
*/
protected fun onPopulateNodeForVirtualView(
virtualViewId:Int, @NonNull node:AccessibilityNodeInfoCompat) {
val rectEle = parentView.virtualIdRectMap.get(virtualViewId)
assert(rectEle != null)
node.setContentDescription("Selected rect " + rectEle.id)
node.setClassName(ImageView::class.java!!.getName())
node.setPackageName(BuildConfig.APPLICATION_ID)
node.setVisibleToUser(true)
node.addAction(AccessibilityActionCompat.ACTION_CLICK)
// *****************************************************************
// It is very important to set the rectangle area for each node so
// the accessibility service knows where to set accessibility focus.
// *****************************************************************
node.setBoundsInParent(
Objects.requireNonNull(parentView.virtualIdRectMap.get(
virtualViewId)).rect)
}
protected fun getVirtualViewAt(x:Float, y:Float):Int {
for (mapElement in parentView.virtualIdRectMap.entrySet())
{
val rect = mapElement.value.rect
if ((rect.left <= x && x <= rect.right
&& rect.top <= y && y <= rect.bottom))
{
return mapElement.value.id
}
}
return ExploreByTouchHelper.INVALID_ID
}
protected fun getVisibleVirtualViews(virtualViewIds:List<Int>) {
for (mapElement in parentView.virtualIdRectMap.entrySet())
{
virtualViewIds.add(mapElement.key)
}
}
protected fun onPerformActionForVirtualView(
virtualViewId:Int, action:Int, @Nullable arguments:Bundle):Boolean {
when (action) {
// After Talkback is turned on, if you want to handle
// DPAD_CENTER key event with your own logic,
// implement it under ACTION_CLICK action.
AccessibilityNodeInfoCompat.ACTION_CLICK -> {
Log.e(TAG, "ACTION_CLICK action handled here.")
return true
}
}
// All the DPAD directional keys are handled by
// Accessibility based on the AccessibilityNodeInfo Tree
// defined above.
// fall through
return false
}
}
Java
package com.example.tvcustomviews;
import android.graphics.Rect;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat;
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat.AccessibilityActionCompat;
import androidx.customview.widget.ExploreByTouchHelper;
import com.example.tvcustomviews.SampleCustomView.VirtualRect;
import java.util.List;
import java.util.Map;
import java.util.Objects;
class SampleExploreByTouchHelper extends ExploreByTouchHelper {
private final String TAG = SampleExploreByTouchHelper.class.getName();
private SampleCustomView parentView;
SampleExploreByTouchHelper(SampleCustomView parentView) {
super(parentView);
this.parentView = parentView;
}
/**
* Define AccessibilityNodeInfo objects with necessary attributes.
* Set required attributes into the AccessibilityNodeInfo for the UI
* component whose virtualID is the virtualViewId.
* @param virtualViewId: virtual ID for the component.
* @param node: the AccessibilityNodeInfoCompat used to set the attribute.
*/
@Override
protected void onPopulateNodeForVirtualView(
int virtualViewId, @NonNull AccessibilityNodeInfoCompat node) {
VirtualRect rectEle = parentView.virtualIdRectMap.get(virtualViewId);
assert rectEle != null;
node.setContentDescription("Selected rect " + rectEle.id);
node.setClassName(ImageView.class.getName());
node.setPackageName(BuildConfig.APPLICATION_ID);
node.setVisibleToUser(true);
node.addAction(AccessibilityActionCompat.ACTION_CLICK);
// *****************************************************************
// It is very important to set the rectangle area for each node so
// the accessibility service knows where to set accessibility focus.
// *****************************************************************
node.setBoundsInParent(
Objects.requireNonNull(parentView.virtualIdRectMap.get(
virtualViewId)).rect);
}
@Override
protected int getVirtualViewAt(float x, float y) {
for (Map.Entry<Integer, VirtualRect> mapElement :
parentView.virtualIdRectMap.entrySet()) {
Rect rect = mapElement.getValue().rect;
if (rect.left <= x && x <= rect.right
&& rect.top <= y && y <= rect.bottom) {
return mapElement.getValue().id;
}
}
return ExploreByTouchHelper.INVALID_ID;
}
@Override
protected void getVisibleVirtualViews(List<Integer> virtualViewIds) {
for (Map.Entry<Integer, VirtualRect> mapElement :
parentView.virtualIdRectMap.entrySet()) {
virtualViewIds.add(mapElement.getKey());
}
}
@Override
protected boolean onPerformActionForVirtualView(
int virtualViewId, int action, @Nullable Bundle arguments) {
switch (action) {
// After Talkback is turned on, if you want to handle
// DPAD_CENTER key event with your own logic,
// implement it under ACTION_CLICK action.
case AccessibilityNodeInfoCompat.ACTION_CLICK:
Log.e(TAG, "ACTION_CLICK action handled here.");
return true;
// All the DPAD directional keys are handled by
// Accessibility based on the AccessibilityNodeInfo Tree
// defined above.
default:
// fall through
}
return false;
}
}
Finally, invoke setAccessibilityDelegate() when instantiating the custom view.
Kotlin
private fun init(@Nullable attrs:AttributeSet) {
...
ViewCompat.setAccessibilityDelegate(this,
SampleExploreByTouchHelper(this))
}
Java
private void init(@Nullable AttributeSet attrs) {
...
ViewCompat.setAccessibilityDelegate(this,
new SampleExploreByTouchHelper(this));
}
With Talkback enabled, accessibility focus is now correctly able to navigate to
the four images inside the custom view. If you press the DPAD_CENTER key on a
keypad, the app registers this event as an ACTION_CLICK event.