The file containing the source code shown below is located in the corresponding directory in <sdk>/samples/android-<version>/...
/*
* Copyright (C) 2011 The Android开源工程
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.apis.accessibility;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Build;
import android.os.Bundle;
import android.text.Layout;
import android.text.StaticLayout;
import android.text.TextPaint;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;
import com.example.android.apis.R;
/**
* Demonstrates how to implement accessibility support of custom views. Custom view
* is a tailored widget developed by extending the base classes in the android.view
* package. This sample shows how to implement the accessibility behavior via both
* inheritance (non backwards compatible) and composition (backwards compatible).
* <p>
* While the Android framework has a diverse portfolio of views tailored for various
* use cases, sometimes a developer needs a specific functionality not implemented
* by the standard views. A solution is to write a custom view that extends one the
* base view classes. While implementing the desired functionality a developer should
* also implement accessibility support for that new functionality such that
* disabled users can leverage it.
* </p>
*/
public class CustomViewAccessibilityActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.custom_view_accessibility);
}
/**
* Demonstrates how to enhance the accessibility support via inheritance.
* <p>
* <strong>Note:</strong> Using inheritance may break your application's
* backwards compatibility. In particular, overriding a method that takes as
* an argument or returns a class not present on an older platform
* version will prevent your application from running on that platform.
* For example, {@link AccessibilityNodeInfo} was introduced in
* {@link Build.VERSION_CODES#ICE_CREAM_SANDWICH API 14}, thus overriding
* {@link View#onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo)
* View.onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo)}
* will prevent you application from running on a platform older than
* {@link Build.VERSION_CODES#ICE_CREAM_SANDWICH API 14}.
* </p>
*/
public static class AccessibleCompoundButtonInheritance extends BaseToggleButton {
public AccessibleCompoundButtonInheritance(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
// We called the super implementation to let super classes
// set appropriate event properties. Then we add the new property
// (checked) which is not supported by a super class.
event.setChecked(isChecked());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
// We called the super implementation to let super classes set
// appropriate info properties. Then we add our properties
// (checkable and checked) which are not supported by a super class.
info.setCheckable(true);
info.setChecked(isChecked());
// Very often you will need to add only the text on the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
info.setText(text);
}
}
@Override
public void onPopulateAccessibilityEvent(AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(event);
// We called the super implementation to populate its text to the
// event. Then we add our text not present in a super class.
// Very often you will need to add only the text on the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
event.getText().add(text);
}
}
}
/**
* Demonstrates how to enhance the accessibility support via composition.
* <p>
* <strong>Note:</strong> Using composition ensures that your application is
* backwards compatible. The android-support-v4 library has API that allow
* using the accessibility APIs in a backwards compatible manner.
* </p>
*/
public static class AccessibleCompoundButtonComposition extends BaseToggleButton {
public AccessibleCompoundButtonComposition(Context context, AttributeSet attrs) {
super(context, attrs);
tryInstallAccessibilityDelegate();
}
public void tryInstallAccessibilityDelegate() {
// If the API version of the platform we are running is too old
// and does not support the AccessibilityDelegate APIs, do not
// call View.setAccessibilityDelegate(AccessibilityDelegate) or
// refer to AccessibilityDelegate, otherwise an exception will
// be thrown.
// NOTE: The android-support-v4 library contains APIs the enable
// using the accessibility APIs in a backwards compatible fashion.
if (Build.VERSION.SDK_INT < 14) {
return;
}
// AccessibilityDelegate allows clients to override its methods that
// correspond to the accessibility methods in View and register the
// delegate in the View essentially injecting the accessibility support.
setAccessibilityDelegate(new AccessibilityDelegate() {
@Override
public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(host, event);
// We called the super implementation to let super classes
// set appropriate event properties. Then we add the new property
// (checked) which is not supported by a super class.
event.setChecked(isChecked());
}
@Override
public void onInitializeAccessibilityNodeInfo(View host,
AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(host, info);
// We called the super implementation to let super classes set
// appropriate info properties. Then we add our properties
// (checkable and checked) which are not supported by a super class.
info.setCheckable(true);
info.setChecked(isChecked());
// Very often you will need to add only the text on the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
info.setText(text);
}
}
@Override
public void onPopulateAccessibilityEvent(View host, AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(host, event);
// We called the super implementation to populate its text to the
// event. Then we add our text not present in a super class.
// Very often you will need to add only the text on the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
event.getText().add(text);
}
}
});
}
}
/**
* This is a base toggle button class whose accessibility is not tailored
* to reflect the new functionality it implements.
* <p>
* <strong>Note:</strong> This is not a sample implementation of a toggle
* button, rather a simple class needed to demonstrate how to refine the
* accessibility support of a custom View.
* </p>
*/
private static class BaseToggleButton extends View {
private boolean mChecked;
private CharSequence mTextOn;
private CharSequence mTextOff;
private Layout mOnLayout;
private Layout mOffLayout;
private TextPaint mTextPaint;
public BaseToggleButton(Context context, AttributeSet attrs) {
this(context, attrs, android.R.attr.buttonStyle);
}
public BaseToggleButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mTextPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
TypedValue typedValue = new TypedValue();
context.getTheme().resolveAttribute(android.R.attr.textSize, typedValue, true);
final int textSize = (int) typedValue.getDimension(
context.getResources().getDisplayMetrics());
mTextPaint.setTextSize(textSize);
context.getTheme().resolveAttribute(android.R.attr.textColorPrimary, typedValue, true);
final int textColor = context.getResources().getColor(typedValue.resourceId);
mTextPaint.setColor(textColor);
mTextOn = context.getString(R.string.accessibility_custom_on);
mTextOff = context.getString(R.string.accessibility_custom_off);
}
public boolean isChecked() {
return mChecked;
}
public CharSequence getText() {
return mChecked ? mTextOn : mTextOff;
}
@Override
public boolean performClick() {
final boolean handled = super.performClick();
if (!handled) {
mChecked ^= true;
invalidate();
}
return handled;
}
@Override
public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
if (mOnLayout == null) {
mOnLayout = makeLayout(mTextOn);
}
if (mOffLayout == null) {
mOffLayout = makeLayout(mTextOff);
}
final int minWidth = Math.max(mOnLayout.getWidth(), mOffLayout.getWidth())
+ getPaddingLeft() + getPaddingRight();
final int minHeight = Math.max(mOnLayout.getHeight(), mOffLayout.getHeight())
+ getPaddingLeft() + getPaddingRight();
setMeasuredDimension(resolveSizeAndState(minWidth, widthMeasureSpec, 0),
resolveSizeAndState(minHeight, heightMeasureSpec, 0));
}
private Layout makeLayout(CharSequence text) {
return new StaticLayout(text, mTextPaint,
(int) Math.ceil(Layout.getDesiredWidth(text, mTextPaint)),
Layout.Alignment.ALIGN_NORMAL, 1.f, 0, true);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
canvas.translate(getPaddingLeft(), getPaddingRight());
Layout switchText = mChecked ? mOnLayout : mOffLayout;
switchText.draw(canvas);
canvas.restore();
}
}
}