Android事件分发机制

准备工作

对于Android事件处理分为两类:
  1. 对于Activity和View: 只有两种事件:
    分发: dispatchTouchEvent函数
    消费: onTouchEvent函数

  2. 对于ViewGroup: 全部三种事件:
    分发: dispatchTouchEvent函数
    拦截:onInterceptTouchEvent函数
    消费: onTouchEvent函数

重写一个ViewGroup和一个View,代码如下
EventViewGroup.java

public class EventViewGroup extends LinearLayout {
    public EventViewGroup(Context context) {
        super(context);
    }

    public EventViewGroup(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e("event","----------->dispatchTouchEvent:::ViewGroup----" + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.e("event","----------->onInterceptTouchEvent:::ViewGroup----" + ev.getAction());
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e("event","----------->onTouchEvent:::ViewGroup----" + event.getAction());
        return super.onTouchEvent(event);
    }
}

EventView.java

public class EventView extends View {

    public EventView(Context context) {
        super(context);
    }

    public EventView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e("event", "----------->dispatchTouchEvent:::View----" + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e("event", "----------->onTouchEvent:::View----" + event.getAction());
        return super.onTouchEvent(event);
    }
}

MainActivity.java

package com.gerry.dispatchevent;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;

import com.gerry.dispatchevent.view.EventView;
import com.gerry.dispatchevent.view.EventViewB;
import com.gerry.dispatchevent.viewgroup.EventViewGroup;
import com.gerry.dispatchevent.viewgroup.EventViewGroupB;

public class MainActivity extends AppCompatActivity {
    private EventViewGroup evg;
    private EventView ev;

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

        evgA= findViewById(R.id.evg);
        evA= findViewById(R.id.ev);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e("event", "----------->dispatchTouchEvent:::MainActivity----" + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e("event", "----------->onTouchEvent:::MainActivity----" + event.getAction());
        return super.onTouchEvent(event);
    }
}

activity_main.xml




     

        
    

开始分析

0为按下动作,1为抬起动作。

1. 对事件不进行任何修改

  • 触摸Activity
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

结论:

在默认情况下,Activity会把事件向下依次按照层级分发到触摸的最后一个ViewGroup或者View,然后会执行最后一个ViewGroup或者View的onTouchEvent()方法,然后又向上依次按照层级去触发onTouchEvent()事件,中途若没有被消费,就会传递直到activity,整个流程呈U形,隧道式向下分发,然后冒泡式向上处理。

2. 修改ViewGroup的dispatchTouchEvent方法,返回false。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

3. 修改View的dispatchTouchEvent方法,返回false。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

4. 修改ViewGroup的dispatchTouchEvent方法,返回true。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1

  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1

5. 修改View的dispatchTouchEvent方法,返回true。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1
E/event: ----------->onInterceptTouchEvent:::ViewGroup----1
E/event: ----------->dispatchTouchEvent:::View----1

从2,3,4,5可以得出的结论:

  1. 当dispatchTouchEvent返回false时,事件不会继续往下分发,无论是ViewGroup还是View,都会从上一级的onTouchEvent事件向上传递,不会执行自己的onTouchEvent()方法
  2. 当dispatchTouchEvent返回true时,表示事件直接被消费,这个事件也就停止分发且不会逆向向上传递,直接结束了。
  3. 返回super:事件将会继续向下分发,直到事件被消费为止。

6. 修改ViewGroup的onInterceptTouchEvent方法,返回false。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

7. 修改ViewGroup的onInterceptTouchEvent方法,返回true。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

从6,7可以得出的结论:

  1. 当onInterceptTouchEvnt返回false/super(默认)时,事件将会正常向下分发,分发至下级的dispatchTouchEvent方法 再次判断是否分发事件。
  2. 当onInterceptTouchEvent返回true时,表示ViewGroup容器拦截后续事件,会执行该ViewGroup的onTouchEvent()方法然后停止向下分发转而通过onTouchEvent()向上传递,直到最终被消费

8. 修改ViewGroup的onTouchEvent方法,返回false。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

9. 修改ViewGroup的onTouchEvent方法,返回true。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1
E/event: ----------->onTouchEvent:::ViewGroup----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1
E/event: ----------->onTouchEvent:::ViewGroup----1

10. 修改View的onTouchEvent方法,返回false。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1

11. 修改View的onTouchEvent方法,返回true。

  • 触摸ViewGroup
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::ViewGroup----0
E/event: ----------->onTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->onTouchEvent:::MainActivity----1
  • 触摸View
E/event: ----------->dispatchTouchEvent:::MainActivity----0
E/event: ----------->dispatchTouchEvent:::ViewGroup----0
E/event: ----------->onInterceptTouchEvent:::ViewGroup----0
E/event: ----------->dispatchTouchEvent:::View----0
E/event: ----------->onTouchEvent:::View----0
E/event: ----------->dispatchTouchEvent:::MainActivity----1
E/event: ----------->dispatchTouchEvent:::ViewGroup----1
E/event: ----------->onInterceptTouchEvent:::ViewGroup----1
E/event: ----------->dispatchTouchEvent:::View----1
E/event: ----------->onTouchEvent:::View----1

从8,9,10,11可以得出的结论:

  1. 当onTouchEvent返回false/super(默认)时,不消费掉此次事件,事件将会层层向上传递,直到被消费。
  2. 当onTouchEvent返回true时,立即消费掉事件,事件将不会向上传递,事件到此终止。

最终结论

dispatchTouchEvent 分发
  1. 当dispatchTouchEvent返回false时,事件不会继续往下分发,无论是ViewGroup还是View,都会从上一级的onTouchEvent事件向上传递,不会执行自己的onTouchEvent()方法
  2. 当dispatchTouchEvent返回true时,表示事件直接被消费,这个事件也就停止分发且不会逆向向上传递,直接结束了。
  3. 返回super:事件将会继续向下分发,直到事件被消费为止。
onInterceptTouchEvent 拦截
  1. 当onInterceptTouchEvnt返回false/super(默认)时,事件将会正常向下分发,分发至下级的dispatchTouchEvent方法 再次判断是否分发事件。
  2. 当onInterceptTouchEvent返回true时,表示ViewGroup容器拦截后续事件,会执行该ViewGroup的onTouchEvent()方法然后停止向下分发转而通过onTouchEvent()向上传递,直到最终被消费
onTouchEvent 消费
  1. 当onTouchEvent返回false/super(默认)时,不消费掉此次事件,事件将会层层向上传递,直到被消费。
  2. 当onTouchEvent返回true时,立即消费掉事件,事件将不会向上传递,事件到此终止。

参考链接:
https://www.jianshu.com/p/fc0590afb1bf
https://www.jianshu.com/p/66a80ff0133b

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