关于Android的Accessibility--自定义View

自定义View

自定义view要处理的accessibility细节

• 处理方向控制；
  处理keyevent中的KEYCODE_ENTER和KEYCODE_DPAD_CENTER
• 实现accessibility api；
  sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED)
  sendAccessibilityEventUnchecked()
  dispatchPopulateAccessibilityEvent()
  …（全是view中的方法）
• 发送AccessibilityEvent对象；
  view已经实现点击、长点、聚焦、滑动、HOVER_ENTER、HOVER_EXIT事件
  自定义其他事件，比如slidebar改变数值的时候，需要发送TYPE_VIEW_TEXT_CHANGED
• Populate AccessibilityEvent and AccessibilityNodeInfo
  event包含很多属性，如类名和事件时间，是已经集成的。但是文字之类的需要自己合入，这些文字还是应当尽量简洁

  @Override
  

public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event) {
// Call the super implementation to populate its text to the event, which
// calls onPopulateAccessibilityEvent() on API Level 14 and up.
boolean completed = super.dispatchPopulateAccessibilityEvent(event);

// In case this is running on a API revision earlier that 14, check
// the text content of the event and add an appropriate text
// description for this custom view:
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
    event.getText().add(text);
    return true;
}
return completed;

}

//4.0以上
onPopulateAccessibilityEvent()添加或修改文字内容
onInitializeAccessibilityEvent() 添加事件状态，如是否选中
//额外处理
onInitializeAccessibilityNodeInfo()

ViewCompat.setAccessibilityDelegate(new AccessibilityDelegateCompat() {
@Override
public void onPopulateAccessibilityEvent(View host, AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(host, event);
// We call the super implementation to populate its text for the
// event. Then we add our text not present in a super class.
// Very often you only need to add the text for the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
event.getText().add(text);
}
}
@Override
public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(host, event);
// We call 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,
AccessibilityNodeInfoCompat info) {
super.onInitializeAccessibilityNodeInfo(host, info);
// We call 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());
// Quite often you only need to add the text for the custom view.
CharSequence text = getText();
if (!TextUtils.isEmpty(text)) {
info.setText(text);
}
}
}

如果自定义view，把内部切割成了多个区域，那么Android肯定也不能自动获得具体的区域参数。  
此时需要建立一个虚拟的view结构，实现view.getAccessibilityNodeProvider()，  
ViewCompat.getAccessibilityNodeProvider()  

- 处理自定义touch event  
对于一些特殊需求，对touch event的处理，可能不太符合常规的点击和长点逻辑，此时我们需要单独处理  
首先需要生成一个AccessibilityEvent来处理click操作，然后要让accessibility service能够执行这个操作  
模式如下：

class CustomTouchView extends View {

public CustomTouchView(Context context) {
    super(context);
}

boolean mDownTouch = false;

@Override
public boolean onTouchEvent(MotionEvent event) {
    super.onTouchEvent(event);

    // Listening for the down and up touch events
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mDownTouch = true;
            return true;

        case MotionEvent.ACTION_UP:
            if (mDownTouch) {
                mDownTouch = false;
                performClick(); // Call this method to handle the response, and
                                // thereby enable accessibility services to
                                // perform this action for a user who cannot
                                // click the touchscreen.
                return true;
            }
    }
    return false; // Return false for other touch events
}

@Override
public boolean performClick() {
    // Calls the super implementation, which generates an AccessibilityEvent
    // and calls the onClick() listener on the view, if any
    super.performClick();

    // Handle the action for the custom click here

    return true;
}

}