问题描述

为什么onTouchEvent方法会在dispatchTouchEvent方法之前执行呢？

新建一个类MyButton，该类继承自Button
然后重写其中的onTouchEvent和dispatchTouchEvent方法

 public class MyButton extends Button {

    private Context mContext;

    public MyButton(Context context) {
        super(context);
        this.mContext = context;
    }

    public MyButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.mContext = context;
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Log.d("TTTT", "context:" + mContext + "MyButton|dispatchTouchEvent|return:" + super.dispatchTouchEvent(event) + "|event:DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.d("TTTT", "context:" + mContext + "MyButton|dispatchTouchEvent|return:" + super.dispatchTouchEvent(event) + "|event:MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.d("TTTT", "context:" + mContext + "MyButton|dispatchTouchEvent|return:" + super.dispatchTouchEvent(event) + "|event:UP");
            break;
        }
        Log.d("TTTT", "========================== ");
        return super.dispatchTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Log.d("TTTT", "context:" + mContext + "MyButton|onTouchEvent|return:" + super.onTouchEvent(event) + "|event:DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.d("TTTT", "context:" + mContext + "MyButton|onTouchEvent|return:" + super.onTouchEvent(event) + "|event:MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.d("TTTT", "context:" + mContext + "MyButton|onTouchEvent|return:" + super.onTouchEvent(event) + "|event:UP");
            break;
        }
        return super.onTouchEvent(event);
    }
}

然后将这个Button加入到布局文件中，然后在Activity中给这个Button设置一个onTouchListener

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.testtouchevent.MainActivity" >

    <com.example.testtouchevent.MyButton
        android:id="@+id/bt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="按钮" />

</LinearLayout>

 public class MainActivity extends Activity {

    private Button bt;

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

        bt = (Button) findViewById(R.id.bt);

        bt.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                return false;
            }
        });
    }
}

按下按钮时候，log显式

 03-31 11:51:08.493: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|onTouchEvent|return:true|event:DOWN
03-31 11:51:08.493: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|dispatchTouchEvent|return:true|event:DOWN
03-31 11:51:08.493: D/TTTT(1609): ==========================
03-31 11:51:08.493: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|onTouchEvent|return:true|event:DOWN

松开按钮时候，log显式：

 03-31 11:51:10.285: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|onTouchEvent|return:true|event:UP
03-31 11:51:10.285: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|dispatchTouchEvent|return:true|event:UP
03-31 11:51:10.285: D/TTTT(1609): ==========================
03-31 11:51:10.289: D/TTTT(1609): context:com.example.testtouchevent.MainActivity@528486ecMyButton|onTouchEvent|return:true|event:UP

可见onTouchEvent方法是在dispatchTouchEvent方法之前执行的
可是View的事件传递机制不是dispatchTouchEvent方法先执行用来传递消息的吗？
请问这是怎么回事儿？

解决方案

View 中的dispatchTouchEvent，OnInterceptTouchEvent ,OnTouchEvent方法
Activity调用dispatchTouchEvent()和onTouchEvent()方法
onTouch、onkey、dispatchTouchEvent、dispatchKeyEvent等方法被执行 “两次” 的解决方法

解决方案二：

应该是button是最后一层，没有子类了，事件传递是向子类传递，如果没有子类就会调用onTouchEvent方法

解决方案三：

首先，button的enabled默认为true，那么在没有OnTouchListener或者有OnTouchListener但是返回false的时候，会第一时间传递给onTouchEvent，
第二，当前Button是最后一级，没有子类可派发事件