Android中Touch事件的传递机制

由于之前对于android的事件传递机制不了解，今天正好不忙，赶紧抽出时间来理一下这方面的知识，本文结合demo，对android的事件传递机制进行分析。

在事件传递过程中，离不开以下三个方法：

1.dispatchTouchEvent 分发touchEvent，返回值为true时表示TouchEvent被当前View处理，事件不会向下层传递（包括后续的onInterceptTouchEvent和onTouchEvent），

dispatchTouchEvent会收到后续的ACTION_MOVE和ACTION_UP事件

2.onInterceptTouchEvent 拦截touchEvent，返回true时表示当前View拦截了touchEvent，然后把事件交给当前View的onTouchEvent处理

3.onTouchEvent 处理TouchEvent，返回true时表示当前View消费了此事件，只有消费了前一个事件后才能收到后续事件。

 

为了弄清楚android在各层view的事件传递，我写了一个小demo来分析Activity,ViewGroup,View之间的事件传递。

首先来看一下代码，一个自定义View，画了一个矩形，在dispatchTouchEvent，onTouchEvent中加入日志方便解析。

public class DrawRectView extends View {

    private Paint mPaint;

    public DrawRectView(Context context) {
        super(context);
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    }

    public DrawRectView(Context context, AttributeSet set) {
        super(context, set);
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.v(LogUtils.TAG, "DrawRectView dispatchTouchEvent action=" + event.getAction());
        return super.dispatchTouchEvent(event);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setColor(Color.YELLOW);
        canvas.drawRect(0, 0, 300, 300, mPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.v(LogUtils.TAG, "DrawRectView onTouchEvent action=" + event.getAction());
        return super.onTouchEvent(event);
    }
}

自定义Layout，同样在相关的TouchEvent方法中加入log

public class MyLayout extends RelativeLayout {

    public MyLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.v(LogUtils.TAG, "MyLayout dispatchTouchEvent action=" + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.v(LogUtils.TAG, "MyLayout onInterceptTouchEvent action=" + ev.getAction());
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.v(LogUtils.TAG, "MyLayout onTouchEvent event=" + event.getAction());
        return super.onTouchEvent(event);
    }

接下来是Activity与activity的布局

public class TouchTestActivity extends Activity {

    private DrawRectView mDrawRectView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.touch_test_activity);

        mDrawRectView = (DrawRectView) findViewById(R.id.draw_rect_view);
        mDrawRectView.setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Log.v(LogUtils.TAG, "mDrawRectView OnTouchListener action=" + event.getAction());
                return false;
            }
        });
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.v(LogUtils.TAG, "TouchTestActivity dispatchTouchEvent action=" + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.v(LogUtils.TAG, "TouchTestActivity onTouchEvent action=" + event.getAction());
        return super.onTouchEvent(event);
    }
}

<com.yangy.test.custom_view.MyLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    
    <com.yangy.test.custom_view.DrawRectView
        android:id="@+id/draw_rect_view"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:layout_centerInParent="true" />

</com.yangy.test.custom_view.MyLayout>

当我们按下矩形DrawRectView时，可以看到打印的log信息如下，Android Touch事件自上到下传递，Activity-->ViewGroup-->View

11-24 15:19:40.659: V/--DEBUG--(32570): TouchTestActivity dispatchTouchEvent action=ACTION_DOWN
11-24 15:19:40.659: V/--DEBUG--(32570): MyLayout dispatchTouchEvent action=ACTION_DOWN
11-24 15:19:40.659: V/--DEBUG--(32570): MyLayout onInterceptTouchEvent action=ACTION_DOWN
11-24 15:19:40.659: V/--DEBUG--(32570): DrawRectView dispatchTouchEvent action=ACTION_DOWN
11-24 15:19:40.659: V/--DEBUG--(32570): mDrawRectView OnTouchListener action=ACTION_DOWN
11-24 15:19:40.669: V/--DEBUG--(32570): DrawRectView onTouchEvent action=ACTION_DOWN
11-24 15:19:40.669: V/--DEBUG--(32570): MyLayout onTouchEvent event=ACTION_DOWN
11-24 15:19:40.669: V/--DEBUG--(32570): TouchTestActivity onTouchEvent action=ACTION_DOWN
11-24 15:19:40.689: V/--DEBUG--(32570): TouchTestActivity dispatchTouchEvent action=ACTION_UP
11-24 15:19:40.689: V/--DEBUG--(32570): TouchTestActivity onTouchEvent action=ACTION_UP

根据log信息，我们也就知道了整个View的事件传递流程，可用下图表示，这里值得注意的是没有任何View消耗掉ACTION_DOWN事件，

所以后续的ACTION_MOVE和ACTION_UP事件并不会向下传递了，这个从log中也可看出。

这时把DrawRectView的onTouchEvent方法返回true，则会出现什么结果呢，接着看log

11-24 16:04:03.159: V/--DEBUG--(3037): TouchTestActivity dispatchTouchEvent action=ACTION_DOWN
11-24 16:04:03.159: V/--DEBUG--(3037): MyLayout dispatchTouchEvent action=ACTION_DOWN
11-24 16:04:03.159: V/--DEBUG--(3037): MyLayout onInterceptTouchEvent action=ACTION_DOWN
11-24 16:04:03.159: V/--DEBUG--(3037): DrawRectView dispatchTouchEvent action=ACTION_DOWN
11-24 16:04:03.159: V/--DEBUG--(3037): mDrawRectView OnTouchListener action=ACTION_DOWN
11-24 16:04:03.159: V/--DEBUG--(3037): DrawRectView onTouchEvent action=ACTION_DOWN

11-24 16:04:03.219: V/--DEBUG--(3037): TouchTestActivity dispatchTouchEvent action=ACTION_MOVE
11-24 16:04:03.219: V/--DEBUG--(3037): MyLayout dispatchTouchEvent action=ACTION_MOVE
11-24 16:04:03.219: V/--DEBUG--(3037): MyLayout onInterceptTouchEvent action=ACTION_MOVE
11-24 16:04:03.219: V/--DEBUG--(3037): DrawRectView dispatchTouchEvent action=ACTION_MOVE
11-24 16:04:03.219: V/--DEBUG--(3037): mDrawRectView OnTouchListener action=ACTION_MOVE
11-24 16:04:03.219: V/--DEBUG--(3037): DrawRectView onTouchEvent action=ACTION_MOVE

11-24 16:04:03.249: V/--DEBUG--(3037): TouchTestActivity dispatchTouchEvent action=ACTION_UP
11-24 16:04:03.249: V/--DEBUG--(3037): MyLayout dispatchTouchEvent action=ACTION_UP
11-24 16:04:03.249: V/--DEBUG--(3037): MyLayout onInterceptTouchEvent action=ACTION_UP
11-24 16:04:03.249: V/--DEBUG--(3037): DrawRectView dispatchTouchEvent action=ACTION_UP
11-24 16:04:03.249: V/--DEBUG--(3037): mDrawRectView OnTouchListener action=ACTION_UP
11-24 16:04:03.249: V/--DEBUG--(3037): DrawRectView onTouchEvent action=ACTION_UP

看来DrawRectView的onTouchEvent方法消费掉ACTION_DOWN事件后，ACTION_MOVE与ACTION_UP都传递过来了，而因为消费了事件，所以onTouchEvent 并不会向上传递

 如果在ViewGroup中拦截了TouchEvent事件又会怎么样呢，由下图来说明：

经过本文的说明后，相信你对于android的事件传递机制更了解了吧。