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Android View 事件分发机制 源码解析

时间:2024-3-2 19:19     作者:韩俊     分类: Android


一直想写事件分发机制的文章,不管咋样,也得自己研究下事件分发的源码,写出心得~

首先我们先写个简单的例子来测试View的事件转发的流程~

1、案例

为了更好的研究View的事件转发,我们自定以一个MyButton继承Button,然后把跟事件传播有关的方法进行复写,然后添加上日志~

MyButton

[java] view
plaincopy

package com.example.zhy_event03;

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

public class MyButton extends Button
{
private static final String TAG = MyButton.class.getSimpleName();

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

@Override  
public boolean onTouchEvent(MotionEvent event)  
{  
    int action = event.getAction();  

    switch (action)  
    {  
    case MotionEvent.ACTION_DOWN:  
        Log.e(TAG, "onTouchEvent ACTION_DOWN");  
        break;  
    case MotionEvent.ACTION_MOVE:  
        Log.e(TAG, "onTouchEvent ACTION_MOVE");  
        break;  
    case MotionEvent.ACTION_UP:  
        Log.e(TAG, "onTouchEvent ACTION_UP");  
        break;  
    default:  
        break;  
    }  
    return super.onTouchEvent(event);  
}  

@Override  
public boolean dispatchTouchEvent(MotionEvent event)  
{  
    int action = event.getAction();  

    switch (action)  
    {  
    case MotionEvent.ACTION_DOWN:  
        Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");  
        break;  
    case MotionEvent.ACTION_MOVE:  
        Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");  
        break;  
    case MotionEvent.ACTION_UP:  
        Log.e(TAG, "dispatchTouchEvent ACTION_UP");  
        break;  

    default:  
        break;  
    }  
    return super.dispatchTouchEvent(event);  
}  

}



在onTouchEvent和dispatchTouchEvent中打印了日志~

然后把我们自定义的按钮加到主布局文件中;

布局文件:

[html] view
plaincopy

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android&quot;
xmlns:tools="http://schemas.android.com/tools&quot;
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >

&lt;com.example.zhy_event03.MyButton  
    android:id=&quot;@&#43;id/id_btn&quot;  
    android:layout_width=&quot;wrap_content&quot;  
    android:layout_height=&quot;wrap_content&quot;  
    android:text=&quot;click me&quot; /&gt;  

</LinearLayout>



最后看一眼MainActivity的代码

[java] view
plaincopy

package com.example.zhy_event03;

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

public class MainActivity extends Activity
{
protected static final String TAG = "MyButton";
private Button mButton ;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

    mButton = (Button) findViewById(R.id.id_btn);  
    mButton.setOnTouchListener(new OnTouchListener()  
    {  
        @Override  
        public boolean onTouch(View v, MotionEvent event)  
        {  
            int action = event.getAction();  

            switch (action)  
            {  
            case MotionEvent.ACTION_DOWN:  
                Log.e(TAG, &quot;onTouch ACTION_DOWN&quot;);  
                break;  
            case MotionEvent.ACTION_MOVE:  
                Log.e(TAG, &quot;onTouch ACTION_MOVE&quot;);  
                break;  
            case MotionEvent.ACTION_UP:  
                Log.e(TAG, &quot;onTouch ACTION_UP&quot;);  
                break;  
            default:  
                break;  
            }  

            return false;  
        }  
    });  
}  

}



在MainActivity中,我们还给MyButton设置了OnTouchListener这个监听~

好了,跟View事件相关一般就这三个地方了,一个onTouchEvent,一个dispatchTouchEvent,一个setOnTouchListener;

下面我们运行,然后点击按钮,查看日志输出:

[html] view
plaincopy

08-31 06:09:39.030: E/MyButton(879): dispatchTouchEvent ACTION_DOWN
08-31 06:09:39.030: E/MyButton(879): onTouch ACTION_DOWN
08-31 06:09:39.049: E/MyButton(879): onTouchEvent ACTION_DOWN
08-31 06:09:39.138: E/MyButton(879): dispatchTouchEvent ACTION_MOVE
08-31 06:09:39.138: E/MyButton(879): onTouch ACTION_MOVE
08-31 06:09:39.147: E/MyButton(879): onTouchEvent ACTION_MOVE
08-31 06:09:39.232: E/MyButton(879): dispatchTouchEvent ACTION_UP
08-31 06:09:39.248: E/MyButton(879): onTouch ACTION_UP
08-31 06:09:39.248: E/MyButton(879): onTouchEvent ACTION_UP



我有意点击的时候蹭了一下,不然不会触发MOVE,手抖可能会打印一堆MOVE的日志~~~

好了,可以看到,不管是DOWN,MOVE,UP都会按照下面的顺序执行:

1、dispatchTouchEvent

2、 setOnTouchListener的onTouch

3、onTouchEvent

下面就跟随日志的脚步开始源码的探索~

2、dispatchTouchEvent

首先进入View的dispatchTouchEvent

[java] view
plaincopy

/**

  • Pass the touch screen motion event down to the target view, or this
  • view if it is the target.
  • @param event The motion event to be dispatched.
  • @return True if the event was handled by the view, false otherwise.
    */
    public boolean dispatchTouchEvent(MotionEvent event) {
    if (!onFilterTouchEventForSecurity(event)) {
    return false;
    }

    if (mOnTouchListener != null &amp;&amp; (mViewFlags &amp; ENABLED_MASK) == ENABLED &amp;&amp;  
            mOnTouchListener.onTouch(this, event)) {  
        return true;  
    }  
    return onTouchEvent(event);  

    }



直接看13行:首先判断mOnTouchListener不为null,并且view是enable的状态,然后 mOnTouchListener.onTouch(this, event)返回true,这三个条件如果都满足,直接return true ; 也就是下面的onTouchEvent(event)不会被执行了;

那么mOnTouchListener是和方神圣,我们来看看:

[java] view
plaincopy

/**

  • Register a callback to be invoked when a touch event is sent to this view.
  • @param l the touch listener to attach to this view
    */
    public void setOnTouchListener(OnTouchListener l) {
    mOnTouchListener = l;
    }

其实就是我们在Activity中设置的setOnTouchListener。

也就是说:如果我们设置了setOnTouchListener,并且return true,那么View自己的onTouchEvent就不会被执行了,当然了,本例我们return false,我们还得往下探索 ;

已经解决一个常见的问题:View的onTouchListener和onTouchEvent的调用关系,相信大家应该已经明白了~let's go;继续往下。

3、View的onTouchEvent:

接下来是View的onTouchEvent:

[java] view
plaincopy

/**

  • Implement this method to handle touch screen motion events.
  • @param event The motion event.
  • @return True if the event was handled, false otherwise.
    */
    public boolean onTouchEvent(MotionEvent event) {
    final int viewFlags = mViewFlags;

    if ((viewFlags &amp; ENABLED_MASK) == DISABLED) {  
        // A disabled view that is clickable still consumes the touch  
        // events, it just doesn't respond to them.  
        return (((viewFlags &amp; CLICKABLE) == CLICKABLE ||  
                (viewFlags &amp; LONG_CLICKABLE) == LONG_CLICKABLE));  
    }  
    
    if (mTouchDelegate != null) {  
        if (mTouchDelegate.onTouchEvent(event)) {  
            return true;  
        }  
    }  
    
    if (((viewFlags &amp; CLICKABLE) == CLICKABLE ||  
            (viewFlags &amp; LONG_CLICKABLE) == LONG_CLICKABLE)) {  
        switch (event.getAction()) {  
            case MotionEvent.ACTION_UP:  
                boolean prepressed = (mPrivateFlags &amp; PREPRESSED) != 0;  
                if ((mPrivateFlags &amp; PRESSED) != 0 || prepressed) {  
                    // take focus if we don't have it already and we should in  
                    // touch mode.  
                    boolean focusTaken = false;  
                    if (isFocusable() &amp;&amp; isFocusableInTouchMode() &amp;&amp; !isFocused()) {  
                        focusTaken = requestFocus();  
                    }  
    
                    if (!mHasPerformedLongPress) {  
                        // This is a tap, so remove the longpress check  
                        removeLongPressCallback();  
    
                        // Only perform take click actions if we were in the pressed state  
                        if (!focusTaken) {  
                            // Use a Runnable and post this rather than calling  
                            // performClick directly. This lets other visual state  
                            // of the view update before click actions start.  
                            if (mPerformClick == null) {  
                                mPerformClick = new PerformClick();  
                            }  
                            if (!post(mPerformClick)) {  
                                performClick();  
                            }  
                        }  
                    }  
    
                    if (mUnsetPressedState == null) {  
                        mUnsetPressedState = new UnsetPressedState();  
                    }  
    
                    if (prepressed) {  
                        mPrivateFlags |= PRESSED;  
                        refreshDrawableState();  
                        postDelayed(mUnsetPressedState,  
                                ViewConfiguration.getPressedStateDuration());  
                    } else if (!post(mUnsetPressedState)) {  
                        // If the post failed, unpress right now  
                        mUnsetPressedState.run();  
                    }  
                    removeTapCallback();  
                }  
                break;  
    
            case MotionEvent.ACTION_DOWN:  
                if (mPendingCheckForTap == null) {  
                    mPendingCheckForTap = new CheckForTap();  
                }  
                mPrivateFlags |= PREPRESSED;  
                mHasPerformedLongPress = false;  
                postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());  
                break;  
    
            case MotionEvent.ACTION_CANCEL:  
                mPrivateFlags &amp;= ~PRESSED;  
                refreshDrawableState();  
                removeTapCallback();  
                break;  
    
            case MotionEvent.ACTION_MOVE:  
                final int x = (int) event.getX();  
                final int y = (int) event.getY();  
    
                // Be lenient about moving outside of buttons  
                int slop = mTouchSlop;  
                if ((x &lt; 0 - slop) || (x &gt;= getWidth() &#43; slop) ||  
                        (y &lt; 0 - slop) || (y &gt;= getHeight() &#43; slop)) {  
                    // Outside button  
                    removeTapCallback();  
                    if ((mPrivateFlags &amp; PRESSED) != 0) {  
                        // Remove any future long press/tap checks  
                        removeLongPressCallback();  
    
                        // Need to switch from pressed to not pressed  
                        mPrivateFlags &amp;= ~PRESSED;  
                        refreshDrawableState();  
                    }  
                }  
                break;  
        }  
        return true;  
    }  
    
    return false;  

    }

代码还是比较长的,

10-15行,如果当前View是Disabled状态且是可点击则会消费掉事件(return true);可以忽略,不是我们的重点;

17-21行,如果设置了mTouchDelegate,则会将事件交给代理者处理,直接return true,如果大家希望自己的View增加它的touch范围,可以尝试使用TouchDelegate,这里也不是重点,可以忽略;

接下来到我们的重点了:

23行的判断:如果我们的View可以点击或者可以长按,则,注意IF的范围,最终一定return true ;

if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
//...
return true;
}

接下来就是 switch (event.getAction())了,判断事件类型,DOWN,MOVE,UP等;

我们按照例子执行的顺序,先看 case MotionEvent.ACTION_DOWN (71-78行):

1、MotionEvent.ACTION_DOWN

75行:给mPrivateFlags设置一个PREPRESSED的标识

76行:设置mHasPerformedLongPress=false;表示长按事件还未触发;

77行:发送一个延迟为ViewConfiguration.getTapTimeout()的延迟消息,到达延时时间后会执行CheckForTap()里面的run方法:

1、ViewConfiguration.getTapTimeout()为115毫秒;

2、CheckForTap

[java] view
plaincopy

private final class CheckForTap implements Runnable {
public void run() {
mPrivateFlags &= ~PREPRESSED;
mPrivateFlags |= PRESSED;
refreshDrawableState();
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
postCheckForLongClick(ViewConfiguration.getTapTimeout());
}
}
}

在run方法里面取消mPrivateFlags的PREPRESSED,然后设置PRESSED标识,刷新背景,如果View支持长按事件,则再发一个延时消息,检测长按;

[java] view
plaincopy

private void postCheckForLongClick(int delayOffset) {
mHasPerformedLongPress = false;

   if (mPendingCheckForLongPress == null) {  
       mPendingCheckForLongPress = new CheckForLongPress();  
   }  
   mPendingCheckForLongPress.rememberWindowAttachCount();  
   postDelayed(mPendingCheckForLongPress,  
           ViewConfiguration.getLongPressTimeout() - delayOffset);  

}


[java] view
plaincopy

class CheckForLongPress implements Runnable {

    private int mOriginalWindowAttachCount;  

    public void run() {  
        if (isPressed() &amp;&amp; (mParent != null)  
                &amp;&amp; mOriginalWindowAttachCount == mWindowAttachCount) {  
            if (performLongClick()) {  
                mHasPerformedLongPress = true;  
            }  
        }  
    }  



可以看到,当用户按下,首先会设置标识为PREPRESSED

如果115后,没有抬起,会将View的标识设置为PRESSED且去掉PREPRESSED标识,然后发出一个检测长按的延迟任务,延时为:ViewConfiguration.getLongPressTimeout() - delayOffset(500ms -115ms),这个115ms刚好时检测额PREPRESSED时间;也就是用户从DOWN触发开始算起,如果500ms内没有抬起则认为触发了长按事件:

1、如果此时设置了长按的回调,则执行长按时的回调,且如果长按的回调返回true;才把mHasPerformedLongPress置为ture;

2、否则,如果没有设置长按回调或者长按回调返回的是false;则mHasPerformedLongPress依然是false;

好了DOWN就分析完成了;大家回个神,下面回到VIEW的onTouchEvent中的ACTION_MOVE:

2、MotionEvent.ACTION_MOVE

86到105行:

87-88行:拿到当前触摸的x,y坐标;

91行判断当然触摸点有没有移出我们的View,如果移出了:

1、执行removeTapCallback();

2、然后判断是否包含PRESSED标识,如果包含,移除长按的检查:removeLongPressCallback();

3、最后把mPrivateFlags中PRESSED标识去除,刷新背景;

[java] view
plaincopy

private void removeTapCallback() {
if (mPendingCheckForTap != null) {
mPrivateFlags &= ~PREPRESSED;
removeCallbacks(mPendingCheckForTap);
}
}

这个是移除,DOWN触发时设置的PREPRESSED的检测;即当前触发时机在DOWN触发不到115ms时,你就已经移出控件外了;

如果115ms后,你才移出控件外,则你的当前mPrivateFlags一定为PRESSED且发送了长按的检测;

就会走上面的2和3;首先移除removeLongPressCallback()
private void removeLongPressCallback() {
if (mPendingCheckForLongPress != null) {
removeCallbacks(mPendingCheckForLongPress);
}
}

然后把mPrivateFlags中PRESSED标识去除,刷新背景;

好了,MOVE我们也分析完成了,总结一下:只要用户移出了我们的控件:则将mPrivateFlags取出PRESSED标识,且移除所有在DOWN中设置的检测,长按等;

下面再回个神,回到View的onTouchEvent的ACTION_UP:

3、MotionEvent.ACTION_UP

26到69行:

27行:判断mPrivateFlags是否包含PREPRESSED

28行:如果包含PRESSED或者PREPRESSED则进入执行体,也就是无论是115ms内或者之后抬起都会进入执行体。

36行:如果mHasPerformedLongPress没有被执行,进入IF

38行:removeLongPressCallback();移除长按的检测

45-50行:如果mPerformClick如果mPerformClick为null,初始化一个实例,然后立即通过handler添加到消息队列尾部,如果添加失败则直接执行 performClick();添加成功,在mPerformClick的run方法中就是执行performClick();

终于执行了我们的click事件了,下面看一下performClick()方法:

[java] view
plaincopy

public boolean performClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

   if (mOnClickListener != null) {  
       playSoundEffect(SoundEffectConstants.CLICK);  
       mOnClickListener.onClick(this);  
       return true;  
   }  

   return false;  

}



if (mOnClickListener != null) {

mOnClickListener.onClick(this);

return true;

}

久违了~我们的mOnClickListener ;

别激动,还没结束,回到ACTION_UP,

58行:如果prepressed为true,进入IF体:

为mPrivateFlags设置表示为PRESSED,刷新背景,125毫秒后执行mUnsetPressedState

否则:mUnsetPressedState.run();立即执行;也就是不管咋样,最后mUnsetPressedState.run()都会执行;

看看这个UnsetPressedState主要干什么:

private final class UnsetPressedState implements Runnable {
public void run() {
setPressed(false);
}
}

public void setPressed(boolean pressed) {
if (pressed) {
mPrivateFlags |= PRESSED;
} else {
mPrivateFlags &= ~PRESSED;
}
refreshDrawableState();
dispatchSetPressed(pressed);
}

把我们的mPrivateFlags中的PRESSED取消,然后刷新背景,把setPress转发下去。

ACTION_UP的最后一行:removeTapCallback(),如果mPendingCheckForTap不为null,移除;

4、总结

好了,代码跨度还是相当大的,下面需要总结下:

1、整个View的事件转发流程是:

View.dispatchEvent->View.setOnTouchListener->View.onTouchEvent

在dispatchTouchEvent中会进行OnTouchListener的判断,如果OnTouchListener不为null且返回true,则表示事件被消费,onTouchEvent不会被执行;否则执行onTouchEvent。

2、onTouchEvent中的DOWN,MOVE,UP

DOWN时:

a、首先设置标志为PREPRESSED,设置mHasPerformedLongPress=false ;然后发出一个115ms后的mPendingCheckForTap;

b、如果115ms内没有触发UP,则将标志置为PRESSED,清除PREPRESSED标志,同时发出一个延时为500-115ms的,检测长按任务消息;

c、如果500ms内(从DOWN触发开始算),则会触发LongClickListener:

此时如果LongClickListener不为null,则会执行回调,同时如果LongClickListener.onClick返回true,才把mHasPerformedLongPress设置为true;否则mHasPerformedLongPress依然为false;

MOVE时:

主要就是检测用户是否划出控件,如果划出了:

115ms内,直接移除mPendingCheckForTap;

115ms后,则将标志中的PRESSED去除,同时移除长按的检查:removeLongPressCallback();

UP时:

a、如果115ms内,触发UP,此时标志为PREPRESSED,则执行UnsetPressedState,setPressed(false);会把setPress转发下去,可以在View中复写dispatchSetPressed方法接收;

b、如果是115ms-500ms间,即长按还未发生,则首先移除长按检测,执行onClick回调;

c、如果是500ms以后,那么有两种情况:

i.设置了onLongClickListener,且onLongClickListener.onClick返回true,则点击事件OnClick事件无法触发;

ii.没有设置onLongClickListener或者onLongClickListener.onClick返回false,则点击事件OnClick事件依然可以触发;

d、最后执行mUnsetPressedState.run(),将setPressed传递下去,然后将PRESSED标识去除;


最后问个问题,然后再运行个例子结束:

1、setOnLongClickListener和setOnClickListener是否只能执行一个

不是的,只要setOnLongClickListener中的onClick返回false,则两个都会执行;返回true则会屏幕setOnClickListener

最后我们给MyButton同时设置setOnClickListener和setOnLongClickListener,运行看看:

[java] view
plaincopy

package com.example.zhy_event03;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnLongClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity
{
protected static final String TAG = "MyButton";
private Button mButton ;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

    mButton = (Button) findViewById(R.id.id_btn);  
    mButton.setOnTouchListener(new OnTouchListener()  
    {  
        @Override  
        public boolean onTouch(View v, MotionEvent event)  
        {  
            int action = event.getAction();  

            switch (action)  
            {  
            case MotionEvent.ACTION_DOWN:  
                Log.e(TAG, &quot;onTouch ACTION_DOWN&quot;);  
                break;  
            case MotionEvent.ACTION_MOVE:  
                Log.e(TAG, &quot;onTouch ACTION_MOVE&quot;);  
                break;  
            case MotionEvent.ACTION_UP:  
                Log.e(TAG, &quot;onTouch ACTION_UP&quot;);  
                break;  
            default:  
                break;  
            }  

            return false;  
        }  
    });  
    mButton.setOnClickListener(new OnClickListener()  
    {  
        @Override  
        public void onClick(View v)  
        {  
            Toast.makeText(getApplicationContext(), &quot;onclick&quot;,Toast.LENGTH_SHORT).show();  
        }  
    });  

    mButton.setOnLongClickListener(new OnLongClickListener()  
    {  
        @Override  
        public boolean onLongClick(View v)  
        {  
            Toast.makeText(getApplicationContext(), &quot;setOnLongClickListener&quot;,Toast.LENGTH_SHORT).show();  
            return false;  
        }  
    });  
}  

}

效果图:


可以看到LongClickListener已经ClickListener都触发了~


最后,本篇博文完成了对View的事件分发机制的整个流程的说明,并且对源码进行了分析;

标签: android

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