Android AccessibilityService源码分析

AccessibilityService首先你要继承AccessibilityService,你会被要求复写

onKeyEvent、onIntercept、onAccessibilityEvent等方法。我们看这些方法在AccessibilityService中是如何实现的。

public class AccessBackKeyService extends AccessibilityService {
        private static final String TAG = "jason";
 
        @Override
        protected boolean onKeyEvent(KeyEvent event) {
            Log.i(TAG, "onKeyEvent");
 
            if(event.getAction() == KeyEvent.ACTION_DOWN){
                return super.onKeyEvent(event);
            }
            Log.i(TAG, "onKeyEvent ACTION_DOWN");
 
            int key = event.getKeyCode();
            switch(key){
                case KeyEvent.KEYCODE_VOLUME_DOWN:
                    Log.i(TAG, "KEYCODE_VOLUME_DOWN");
                    break;
                case KeyEvent.KEYCODE_VOLUME_UP:
                    Log.i(TAG, "KEYCODE_VOLUME_UP");
                    Toast.makeText(this, "KEYCODE_VOLUME_UP", Toast.LENGTH_SHORT).show();
                    break;
                case KeyEvent.KEYCODE_BACK:
 
                    Log.i(TAG, "KEYCODE_BACK");
                    Toast.makeText(this, "KEYCODE_BACK, source:"+event.getSource(), Toast.LENGTH_SHORT).show();
                    break;
                case KeyEvent.KEYCODE_ESCAPE:
                    Log.i(TAG, "KEYCODE_ESCAPE");
                    Toast.makeText(this, "KEYCODE_ESCAPE", Toast.LENGTH_SHORT).show();
                    break;
            }
            return super.onKeyEvent(event);
        }
 
 
 
        @Override
        public void onInterrupt() {
 
        }
 
        @Override
        public void onCreate() {
            super.onCreate();
        }
 
        @Override
        public void onAccessibilityEvent(AccessibilityEvent event) {
            // TODO Auto-generated method stub
 
        }
 
    @Override
    protected boolean onGesture(int gestureId) {
        Log.i("jason", "onGesture:"+gestureId);
        return super.onGesture(gestureId);
    }
}

我们看到AccessibilityService中有一个接口

/**
 * @hide
 */
public interface Callbacks {
    public void onAccessibilityEvent(AccessibilityEvent event);
    public void onInterrupt();
    public void onServiceConnected();
    public void init(int connectionId, IBinder windowToken);
    public boolean onGesture(int gestureId);
    public boolean onKeyEvent(KeyEvent event);
    public void onMagnificationChanged(@NonNull Region region,
            float scale, float centerX, float centerY);
    public void onSoftKeyboardShowModeChanged(int showMode);
    public void onPerformGestureResult(int sequence, boolean completedSuccessfully);
}

AccessibilityService利用观察者模式的形式将自己封装进一个IAccessibilityServiceClientWrapper内部类中，在onBind方法中实现，猜测在辅助功能打开开关的时候，onBind这个方法将被调用，一会我们从源码分析，先分析一下 IAccessibilityServiceClientWrapper 。