Android事件分发机制

作者: gerryjia | 来源:发表于2020-01-02 15:35 被阅读0次

准备工作

对于Android事件处理分为两类：

对于Activity和View：只有两种事件：
分发: dispatchTouchEvent函数
消费: onTouchEvent函数
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

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:orientation="vertical"
    tools:context=".MainActivity">

     <com.gerry.dispatchevent.viewgroup.EventViewGroup
        android:id="@+id/evg"
        android:layout_width="match_parent"
        android:layout_height="500px"
        android:layout_marginTop="250px"
        android:background="@android:color/holo_green_dark"
        android:gravity="center"
        android:orientation="vertical">

        <com.gerry.dispatchevent.view.EventView
            android:id="@+id/ev"
            android:layout_width="200px"
            android:layout_height="150px"
            android:background="@android:color/holo_blue_light" />
    </com.gerry.dispatchevent.viewgroup.EventViewGroup>
</FrameLayout>

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：

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

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。

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：

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。

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：

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。

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

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

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。

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

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。

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

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。

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

Android事件分发机制

准备工作

对于Android事件处理分为两类：

开始分析

1. 对事件不进行任何修改

2. 修改ViewGroup的dispatchTouchEvent方法，返回false。

3. 修改View的dispatchTouchEvent方法，返回false。

4. 修改ViewGroup的dispatchTouchEvent方法，返回true。

5. 修改View的dispatchTouchEvent方法，返回true。

6. 修改ViewGroup的onInterceptTouchEvent方法，返回false。

7. 修改ViewGroup的onInterceptTouchEvent方法，返回true。

8. 修改ViewGroup的onTouchEvent方法，返回false。

9. 修改ViewGroup的onTouchEvent方法，返回true。

10. 修改View的onTouchEvent方法，返回false。

11. 修改View的onTouchEvent方法，返回true。

最终结论

dispatchTouchEvent 分发

onInterceptTouchEvent 拦截

onTouchEvent 消费

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