Android的事件分發機制

Android的事件有點選事件、滑動事件等，這些都是由觸摸事件組成的，如點選事件就是由觸摸ACTION_DOWN(按下螢幕事件)和ACTION_UP（離開事件）組成。

以下分析一下Android事件分發機制，先post上一些代碼：

父容器，繼承ViewGroup，重寫了dispatchTouchEvent(MotionEvent ev)，onInterceptTouchEvent(MotionEvent ev)和onTouchEvent(MotionEvent ev)函數

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，繼承View，重寫了dispatchTouchEvent(MotionEvent ev)，onTouchEvent(MotionEvent ev)函數

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)傳回值:" + childEvent +" TouchEventChilds | onTouchEvent --> " + TouchEventUtil.getTouchAction(ev.getAction()));
        return false;
    }

}

Activity頁面，布局裡有一個父容器和子控件，并且分别實作了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);
    }

}

運作程式，列印出來的資訊為：

- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: child | onTouch --> ACTION_DOWN
- ::: I/System.out(): zrp: super.onTouchEvent(ev)傳回值:true TouchEventChilds | onTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: child | onTouch --> ACTION_UP
- ::: I/System.out(): zrp: super.onTouchEvent(ev)傳回值:true TouchEventChilds | onTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: child | onclick -->

事件分發事件：1.ACTION_DOWN的事件傳遞：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) ;

接下來是ACTION_UP的事件傳遞：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後，會把事件傳遞給OnClickListener的onclick

如果子控件的onTouch傳回true，列印資訊為

- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: child | onTouch --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: child | onTouch --> ACTION_UP

onTouchEvent沒有被調用，最終up事件沒有傳遞到OnClickListener的onClick。

子控件onTouchEvent預設傳回true，就是允許消費事件，若傳回false，子控件不消費接下來的事件。列印的消息為：

- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | onInterceptTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp:  TouchEventChilds | dispatchTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: child | onTouch --> ACTION_DOWN
- ::: I/System.out(): zrp: super.onTouchEvent(ev)傳回值:true TouchEventChilds | onTouchEvent --> ACTION_DOWN
- ::: I/System.out(): zrp: father | onTouch --> ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventFather | onTouchEvent -->ACTION_DOWN
- ::: I/System.out(): zrp: TouchEventActivity | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | dispatchTouchEvent --> ACTION_UP
- ::: I/System.out(): zrp: father | onTouch --> ACTION_UP
- ::: I/System.out(): zrp: TouchEventFather | onTouchEvent -->ACTION_UP
- ::: I/System.out(): zrp: father | onclick -->

總結：子控件不消費事件，會把事件傳遞給父容器，接下來的事件都會傳遞給父容器。若子控件消費事件，不會把事件傳遞給父容器，則父容器onTouchEvent、onTouch和onClick方法不會被調用。

完整demo：http://download.csdn.net/detail/chen20142015/9801799

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