1209-View：事件分发机制二

先看示例代码

<?xml version="1.0" encoding="utf-8"?>
<com.fy.example.touchevent.view.TouchRelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.fy.example.touchevent.view.TouchTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, my TouchEventDemo!" />
</com.fy.example.touchevent.view.TouchRelativeLayout>

两个自定义控件，重写了相关方法，便于考察事件分发

public class MainActivity extends AppCompatActivity {

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

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.d("MainActivity", "dispatchTouchEvent()");
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d("MainActivity", "onTouchEvent()");
        return super.onTouchEvent(event);
    }
}

public class TouchRelativeLayout extends RelativeLayout {

    public TouchRelativeLayout(Context context) {
        super(context);
    }
    public TouchRelativeLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public TouchRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.d("TouchRelativeLayout", "dispatchTouchEvent()");
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.d("TouchRelativeLayout", "onInterceptTouchEvent()");
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d("TouchRelativeLayout", "onTouchEvent()");
        return super.onTouchEvent(event);
    }
}

public class TouchTextView extends TextView {

    public TouchTextView(Context context) {
        super(context);
    }
    public TouchTextView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public TouchTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.d("TouchTextView", "dispatchTouchEvent()");
        return super.dispatchTouchEvent(ev);
    }

    @Override
        public boolean onTouchEvent(MotionEvent event) {
        Log.d("TouchTextView", "onTouchEvent()");
        return false;
    }
}

点击一下界面中的文本，日志打印如下

12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/MainActivity: dispatchTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/TouchRelativeLayout: dispatchTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/TouchRelativeLayout: onInterceptTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/TouchTextView: dispatchTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/TouchTextView: onTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/TouchRelativeLayout: onTouchEvent()
12-09 03:13:22.153 1673-1673/com.fy.example.touchevent D/MainActivity: onTouchEvent()
12-09 03:13:22.235 1673-1673/com.fy.example.touchevent D/MainActivity: dispatchTouchEvent()
12-09 03:13:22.235 1673-1673/com.fy.example.touchevent D/MainActivity: onTouchEvent()
12-09 03:13:22.253 1673-1673/com.fy.example.touchevent D/MainActivity: dispatchTouchEvent()
12-09 03:13:22.253 1673-1673/com.fy.example.touchevent D/MainActivity: onTouchEvent()

可见，事件传递过程是由外向内，即事件总是先传递给父元素，然后由父元素分发给子元素。

而由于TextView是不可点击的，它的onTouchEvent默认返回false，这样事件被层层抛上来，最终交给Activity处理。