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?

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

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

 public class MyButton extends Button {
 
    。。。。。省略代码。。。。。。
 
    @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);
    }
 
   。。。。。省略代码。。。。。。
}

onTouchEvent方法会在dispatchTouchEvent方法之前执行是因为你在打印日志的时候调用了super.super.dispatchTouchEvent(event)

即在DOWN和UP打印日志的代码:

 Log.d("TTTT", "context:" + mContext + "MyButton|dispatchTouchEvent|return:" + super.dispatchTouchEvent(event) + "|event:DOWN");
 Log.d("TTTT", "context:" + mContext + "MyButton|dispatchTouchEvent|return:" + super.dispatchTouchEvent(event) + "|event:UP");

这时候会调用MyButton的父类View的dispatchTouchEvent方法

 public boolean dispatchTouchEvent(MotionEvent event) {
        // If the event should be handled by accessibility focus first.
        if (event.isTargetAccessibilityFocus()) {
            // We don't have focus or no virtual descendant has it, do not handle the event.
            if (!isAccessibilityFocusedViewOrHost()) {
                return false;
            }
            // We have focus and got the event, then use normal event dispatch.
            event.setTargetAccessibilityFocus(false);
        }

        boolean result = false;

        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(event, 0);
        }

        final int actionMasked = event.getActionMasked();
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Defensive cleanup for new gesture
            stopNestedScroll();
        }

        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            //noinspection SimplifiableIfStatement
            ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    && li.mOnTouchListener.onTouch(this, event)) {
                result = true;
            }

            if (!result && onTouchEvent(event)) {
                result = true;
            }
        }

        if (!result && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
        }

        // Clean up after nested scrolls if this is the end of a gesture;
        // also cancel it if we tried an ACTION_DOWN but we didn't want the rest
        // of the gesture.
        if (actionMasked == MotionEvent.ACTION_UP ||
                actionMasked == MotionEvent.ACTION_CANCEL ||
                (actionMasked == MotionEvent.ACTION_DOWN && !result)) {
            stopNestedScroll();
        }

        return result;
    }

 这个时候就调用了MyButton的onTouchEvent方法会先打印 onTouchEvent的日志 

然后再打印 dispatchTouchEvent 日志,在MyButton#dispatchTouchEvent 最后又return super.dispatchTouchEvent(event);

打印你添加的分割线: Log.d("TTTT", "========================== ");

这时又会调用MyButton的onTouchEvent再打印一次 onTouchEvent的日志 

最终得日志就变成了

 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
 

更详细内容我写了一篇文章:https://blog.csdn.net/u011288271/article/details/114395637