Android的事件分发机制

本文详细解析了Android中事件分发机制的工作原理,通过一个具体示例展示了事件如何从Activity传递到ViewGroup及View组件的过程。特别是点击事件的ACTION_DOWN和ACTION_UP状态的变化过程。

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Android的事件有点击事件、滑动事件等,这些都是由触摸事件组成的,如点击事件就是由触摸ACTION_DOWN(按下屏幕事件)和ACTION_UP(离开事件)组成。
以下分析一下Android事件分发机制,先post上一些代码:
父容器,继承ViewGroup,重写了dispatchTouchEvent(MotionEvent ev),onInterceptTouchEvent(MotionEvent ev)和onTouchEvent(MotionEvent ev)函数

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.LinearLayout;

public class TouchEventFather extends LinearLayout {

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

    public TouchEventFather(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public boolean dispatchTouchEvent(MotionEvent ev) {
        LogUtil.d("TouchEventFather | dispatchTouchEvent --> " + TouchEventUtil.getTouchAction(ev.getAction()));
        return super.dispatchTouchEvent(ev);
    }

    public boolean onInterceptTouchEvent(MotionEvent ev) {
        LogUtil.d("TouchEventFather | onInterceptTouchEvent --> " + TouchEventUtil.getTouchAction(ev.getAction()));
        return super.onInterceptTouchEvent(ev);
        //return false;
    }

    public boolean onTouchEvent(MotionEvent ev) {
        LogUtil.d("TouchEventFather | onTouchEvent -->" + TouchEventUtil.getTouchAction(ev.getAction()));
        return super.onTouchEvent(ev);
    }

}

子控件,继承View,重写了dispatchTouchEvent(MotionEvent ev),onTouchEvent(MotionEvent ev)函数

import android.R.bool;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.Button;
import android.widget.LinearLayout;

public class TouchEventChild extends Button {

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

    public TouchEventChild(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public boolean dispatchTouchEvent(MotionEvent ev) {
        LogUtil.d(" TouchEventChilds | dispatchTouchEvent --> " + TouchEventUtil.getTouchAction(ev.getAction()));

        //super.dispatchTouchEvent(ev);
        return super.dispatchTouchEvent(ev);
        //return true;
    }


    public boolean onTouchEvent(MotionEvent ev) {
        boolean childEvent = super.onTouchEvent(ev);
        LogUtil.d("super.onTouchEvent(ev)返回值:" + childEvent +" TouchEventChilds | onTouchEvent --> " + TouchEventUtil.getTouchAction(ev.getAction()));
        return false;
    }

}

Activity页面,布局里有一个父容器和子控件,并且分别实现了OnClickListener和OnTouchListener接口。

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

public class TouchEventActivity extends Activity {

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TouchEventFather father = (TouchEventFather) findViewById(R.id.father);
        TouchEventChild child = (TouchEventChild) findViewById(R.id.childs);
        Button btn = (Button) findViewById(R.id.btn);

        father.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                LogUtil.d("father | onclick --> ");
            }
        });

        father.setOnTouchListener(new View.OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                LogUtil.d("father | onTouch --> "
                        + TouchEventUtil.getTouchAction(event.getAction()));
                return false;
            }
        });

        child.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                LogUtil.d("child | onclick --> ");
            }
        });

        child.setOnTouchListener(new View.OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                LogUtil.d("child | onTouch --> "
                        + TouchEventUtil.getTouchAction(event.getAction()));
                return false;
            }
        });
    }

    public boolean dispatchTouchEvent(MotionEvent ev) {
        LogUtil.d("TouchEventActivity | dispatchTouchEvent --> "
                + TouchEventUtil.getTouchAction(ev.getAction()));
        return super.dispatchTouchEvent(ev);
    }

    public boolean onTouchEvent(MotionEvent event) {
        LogUtil.d("TouchEventActivity | onTouchEvent --> "
                + TouchEventUtil.getTouchAction(event.getAction()));

        return super.onTouchEvent(event);
    }

}

运行程序,打印出来的信息为:

04-01 21:56:17.921: I/System.out(8054): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
04-01 21:56:17.921: I/System.out(8054): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
04-01 21:56:17.931: I/System.out(8054): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
04-01 21:56:17.931: I/System.out(8054): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
04-01 21:56:17.931: I/System.out(8054): zrp: child | onTouch --> ACTION_DOWN
04-01 21:56:17.931: I/System.out(8054): zrp: super.onTouchEvent(ev)返回值:true TouchEventChilds | onTouchEvent --> ACTION_DOWN
04-01 21:56:17.941: I/System.out(8054): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
04-01 21:56:17.941: I/System.out(8054): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
04-01 21:56:17.941: I/System.out(8054): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_UP
04-01 21:56:17.951: I/System.out(8054): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_UP
04-01 21:56:17.951: I/System.out(8054): zrp: child | onTouch --> ACTION_UP
04-01 21:56:17.951: I/System.out(8054): zrp: super.onTouchEvent(ev)返回值:true TouchEventChilds | onTouchEvent --> ACTION_UP
04-01 21:56:17.961: I/System.out(8054): zrp: child | onclick --> 

事件分发事件:1.ACTION_DOWN的事件传递:Activity的dispatchTouchEvent–>父容器的dispatchTouchEvent–>父容器的onInterceptTouchEvent–>子控件的dispatchTouchEvent–>子控件的OnTouchListener的onTouch–>onTouchEvent(ev) ;
接下来是ACTION_UP的事件传递:dispatchTouchEvent–>父容器的dispatchTouchEvent–>父容器的onInterceptTouchEvent–>子控件的dispatchTouchEvent–>子控件的OnTouchListener的onTouch–>onTouchEvent(ev) –>onclick;
ACTION_DOWN和ACTION_UP后,会把事件传递给OnClickListener的onclick

如果子控件的onTouch返回true,打印信息为

04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
04-01 21:57:40.761: I/System.out(9164): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
04-01 21:57:40.761: I/System.out(9164): zrp: child | onTouch --> ACTION_DOWN
04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
04-01 21:57:40.761: I/System.out(9164): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_UP
04-01 21:57:40.761: I/System.out(9164): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_UP
04-01 21:57:40.761: I/System.out(9164): zrp: child | onTouch --> ACTION_UP

onTouchEvent没有被调用,最终up事件没有传递到OnClickListener的onClick。

子控件onTouchEvent默认返回true,就是允许消费事件,若返回false,子控件不消费接下来的事件。打印的消息为:

04-01 22:00:04.601: I/System.out(9665): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
04-01 22:00:04.611: I/System.out(9665): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
04-01 22:00:04.611: I/System.out(9665): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
04-01 22:00:04.611: I/System.out(9665): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
04-01 22:00:04.611: I/System.out(9665): zrp: child | onTouch --> ACTION_DOWN
04-01 22:00:04.611: I/System.out(9665): zrp: super.onTouchEvent(ev)返回值:true TouchEventChilds | onTouchEvent --> ACTION_DOWN
04-01 22:00:04.621: I/System.out(9665): zrp: father | onTouch --> ACTION_DOWN
04-01 22:00:04.621: I/System.out(9665): zrp: TouchEventFather | onTouchEvent -->ACTION_DOWN
04-01 22:00:04.621: I/System.out(9665): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
04-01 22:00:04.631: I/System.out(9665): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
04-01 22:00:04.631: I/System.out(9665): zrp: father | onTouch --> ACTION_UP
04-01 22:00:04.631: I/System.out(9665): zrp: TouchEventFather | onTouchEvent -->ACTION_UP
04-01 22:00:04.641: I/System.out(9665): zrp: father | onclick --> 

总结:子控件不消费事件,会把事件传递给父容器,接下来的事件都会传递给父容器。若子控件消费事件,不会把事件传递给父容器,则父容器onTouchEvent、onTouch和onClick方法不会被调用。

完整demo:http://download.youkuaiyun.com/detail/chen20142015/9801799

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