迅速理解Android事件传递

最近学习 Android，感觉Android事件传递机制很有意思，搞懂这个基础知识点是必须的，于是收集资料，做个Demo加深印象，记录之。

Demo比较简单，一个ViewGroup上放置一个按钮。

自定义VieGroup继承自LinearLayout:

package com.example.mydispatchtouchevent;import android.content.Context;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.view.View.OnClickListener;import android.view.View.OnTouchListener;import android.view.ViewGroup;import android.widget.LinearLayout;public class MyView extends LinearLayout implements OnClickListener,OnTouchListener{public MyView(Context context) {super(context);setOnClickListener(this);}@Overridepublic void onClick(View v) {Log.i("TAG","viewgroup_doClick");}@Overridepublic boolean onTouch(View v, MotionEvent event) {Log.i("TAG","viewgroup_onTouch="+event.getAction());return false;}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i("TAG","viewgroup_onTouchEvent="+event.getAction());return super.onTouchEvent(event);}@Overridepublic boolean dispatchTouchEvent(MotionEvent event) {Log.i("TAG","viewgroup_dispatchTouchEvent="+event.getAction());return super.dispatchTouchEvent(event);}@Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {Log.i("TAG","viewgroup_onInterceptTouchEvent");return super.onInterceptTouchEvent(ev);}}

自定义Button:

package com.example.mydispatchtouchevent;import android.content.Context;import android.util.Log;import android.widget.Button;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.view.View.OnClickListener;public class MyButton extends Button implements OnTouchListener,OnClickListener {public MyButton(Context context) {super(context);setOnTouchListener(this);setOnClickListener(this);this.setText("测试");}@Overridepublic boolean onTouch(View v, MotionEvent event) {Log.i("TAG", "button_onTouch=" + event.getAction());return false;}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i("TAG", "button_onTouchEvent=" + event.getAction());return super.onTouchEvent(event);//return false;}@Overridepublic void onClick(View v) {Log.i("TAG", "button_doClick");}@Overridepublic boolean dispatchTouchEvent(MotionEvent event) {Log.i("TAG", "button_dispatchTouchEvent=" + event.getAction());return super.dispatchTouchEvent(event);}}

Activity:

package com.example.mydispatchtouchevent;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.view.MotionEvent;import android.view.ViewGroup;import android.widget.Button;import android.widget.LinearLayout;public class MainActivity extends Activity {Button myBtn;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ViewGroup viewGroup = new MyView(this);Button button = new MyButton(this);LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,LinearLayout.LayoutParams.WRAP_CONTENT);button.setLayoutParams(params);viewGroup.addView(button);setContentView(viewGroup);}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i("TAG", "Activity_onTouchEvent=" + event.getAction() + " / "+ "event=" + event.hashCode());return super.onTouchEvent(event);}}

给自定义ViewGroup实现dispatchTouchEvent，onInterceptTouchEvent，onTouch，onTouchEvent，onClick；Button实现dispatchTouchEvent，onTouch，onTouchEvent，onClick，Activity上实现onTouchEvent。

点击按钮，运行结果：

02-16 02:45:18.209: I/TAG(2535): viewgroup_dispatchTouchEvent=002-16 02:45:18.209: I/TAG(2535): viewgroup_onInterceptTouchEvent02-16 02:45:18.209: I/TAG(2535): button_dispatchTouchEvent=002-16 02:45:18.209: I/TAG(2535): button_onTouch=002-16 02:45:18.209: I/TAG(2535): button_onTouchEvent=002-16 02:45:18.313: I/TAG(2535): viewgroup_dispatchTouchEvent=102-16 02:45:18.313: I/TAG(2535): viewgroup_onInterceptTouchEvent02-16 02:45:18.313: I/TAG(2535): button_dispatchTouchEvent=102-16 02:45:18.313: I/TAG(2535): button_onTouch=102-16 02:45:18.313: I/TAG(2535): button_onTouchEvent=102-16 02:45:18.321: I/TAG(2535): button_doClick

顺序一目了然，viewgroup_dispatchTouchEvent先得到event,然后是viewgroup_onInterceptTouchEvent，接下来就把event转交给button,ACTION_DOWN和ACTION_UP各走一遍后，最后执行button_doClick。

这些方法的游戏规则是：如果返回true,event被消化了，不再传递；如果返回false，event交给下一位继续。在button_onTouchEvent中返回了true,事件传递就到此为止，其中button_doClick是在button_onTouchEvent中调用。

button_onTouchEvent修改为：

@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i("TAG", "button_onTouchEvent=" + event.getAction());//return super.onTouchEvent(event);return false;}

点击按钮：

02-16 03:02:38.213: I/TAG(2582): viewgroup_dispatchTouchEvent=002-16 03:02:38.213: I/TAG(2582): viewgroup_onInterceptTouchEvent02-16 03:02:38.213: I/TAG(2582): button_dispatchTouchEvent=002-16 03:02:38.213: I/TAG(2582): button_onTouch=002-16 03:02:38.213: I/TAG(2582): button_onTouchEvent=002-16 03:02:38.213: I/TAG(2582): viewgroup_onTouchEvent=002-16 03:02:38.317: I/TAG(2582): viewgroup_dispatchTouchEvent=102-16 03:02:38.317: I/TAG(2582): viewgroup_onTouchEvent=102-16 03:02:38.317: I/TAG(2582): viewgroup_doClick

这回button_onTouchEvent放水了，使得event继续往下“掉”,button_doClick不再执行，现在执行的是viewgroup_doClick。另外，发现button上只走了一遍ACTION_DOWN,ACTION_UP没它什么事，因为event已经不在button手中了（这么说比较形象）。

还没完，继续，viewgroup_onTouchEvent修改为：

@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.i("TAG","viewgroup_onTouchEvent="+event.getAction());//return super.onTouchEvent(event);return false;}

现在由viewgroup_onTouchEvent接着放水，点击按钮运行下结果：

02-16 03:18:56.737: I/TAG(2631): viewgroup_dispatchTouchEvent=002-16 03:18:56.737: I/TAG(2631): viewgroup_onInterceptTouchEvent02-16 03:18:56.737: I/TAG(2631): button_dispatchTouchEvent=002-16 03:18:56.737: I/TAG(2631): button_onTouch=002-16 03:18:56.737: I/TAG(2631): button_onTouchEvent=002-16 03:18:56.737: I/TAG(2631): viewgroup_onTouchEvent=002-16 03:18:56.737: I/TAG(2631): Activity_onTouchEvent=0 02-16 03:18:56.841: I/TAG(2631): Activity_onTouchEvent=1

现在终于轮到躺地板的Activity接到event了，过程参考上面，应该也比较好理解。

以下内容在stackOveflow找到，用来总结再合适不过了

How theActivityhandles touch:

Activity.dispatchTouchEvent()

Always first to be called

Sends event to root view attached to Window

onTouchEvent()

Called if no views consume the event

Always last to be called

How theViewhandles touch:

View.dispatchTouchEvent()

Sends event to listener first, if exists

View.OnTouchListener.onTouch()

If not consumed, processes the touch itself

View.onTouchEvent()

How aViewGrouphandles touch:

ViewGroup.dispatchTouchEvent()

onInterceptTouchEvent()

Check if it should supersede children

PassesACTION_CANCELto active child

Return true once, consumes all subsequent events

For each child view, in reverse order they were added

If touch is relevant (inside view),child.dispatchTouchEvent()

If not handled by previous, dispatch to next view

If no children handle event, listener gets a chance

OnTouchListener.onTouch()

If no listener, or not handled

onTouchEvent()

Intercepted events jump over child step

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