Android View 事件分发机制 源代码解析 (上)
一直想写事件分发机制的文章,无论咋样,也得自己研究下事件分发的源代码。写出心得~
首先我们先写个简单的样例来測试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。然后加入上日志~
MyButton
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~
然后把我们自己定义的按钮加到主布局文件里;
布局文件:
<LinearLayout 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" tools:context=".MainActivity" > <com.example.zhy_event03.MyButton android:id="@+id/id_btn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="click me" /> </LinearLayout>
最后看一眼MainActivity的代码
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, "onTouch ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onTouch ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "onTouch ACTION_UP"); 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;
以下我们运行,然后点击按钮,查看日志输出:
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。能够看到。无论是DOWN,MOVE,UP都会依照以下的顺序运行:
1、dispatchTouchEvent
2、 setOnTouchListener的onTouch
3、onTouchEvent
以下就尾随日志的脚步開始源代码的探索~
2、dispatchTouchEvent
首先进入View的dispatchTouchEvent
/** * 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 && (mViewFlags & ENABLED_MASK) == ENABLED && mOnTouchListener.onTouch(this, event)) { return true; } return onTouchEvent(event); }
直接看13行:首先推断mOnTouchListener不为null。而且view是enable的状态,然后 mOnTouchListener.onTouch(this, event)返回true。这三个条件假设都满足,直接return true ; 也就是以下的onTouchEvent(event)不会被运行了;
那么mOnTouchListener是和方神圣,我们来看看:
/** * 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; }事实上就是我们在Activity中设置的setOnTouchListener。
也就是说:假设我们设置了setOnTouchListener,而且return true,那么View自己的onTouchEvent就不会被运行了。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确了~let's go;继续往下。
3、View的onTouchEvent:
接下来是View的onTouchEvent:
/** * 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 & ENABLED_MASK) == DISABLED) { // A disabled view that is clickable still consumes the touch // events, it just doesn't respond to them. return (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)); } if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) { switch (event.getAction()) { case MotionEvent.ACTION_UP: boolean prepressed = (mPrivateFlags & PREPRESSED) != 0; if ((mPrivateFlags & PRESSED) != 0 || prepressed) { // take focus if we don't have it already and we should in // touch mode. boolean focusTaken = false; if (isFocusable() && isFocusableInTouchMode() && !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 &= ~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 < 0 - slop) || (x >= getWidth() + slop) || (y < 0 - slop) || (y >= getHeight() + slop)) { // Outside button removeTapCallback(); if ((mPrivateFlags & PRESSED) != 0) { // Remove any future long press/tap checks removeLongPressCallback(); // Need to switch from pressed to not pressed mPrivateFlags &= ~PRESSED; refreshDrawableState(); } } break; } return true; } return false; }
代码还是比較长的,
10-15行,假设当前View是Disabled状态且是可点击则会消费掉事件(return true);能够忽略,不是我们的重点;17-21行。假设设置了mTouchDelegate,则会将事件交给代理者处理,直接return true,假设大家希望自己的View添加它的touch范围,能够尝试使用TouchDelegate,这里也不是重点,能够忽略。
接下来到我们的重点了:
23行的推断:假设我们的View能够点击或者能够长按,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。推断事件类型,DOWN,MOVE,UP等;
我们依照样例运行的顺序,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,到达延时时间后会运行CheckForTap()里面的run方法:
1、ViewConfiguration.getTapTimeout()为115毫秒;
2、CheckForTap
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。假设View支持长按事件。则再发一个延时消息。检測长按;
private void postCheckForLongClick(int delayOffset) { mHasPerformedLongPress = false; if (mPendingCheckForLongPress == null) { mPendingCheckForLongPress = new CheckForLongPress(); } mPendingCheckForLongPress.rememberWindowAttachCount(); postDelayed(mPendingCheckForLongPress, ViewConfiguration.getLongPressTimeout() - delayOffset); }
class CheckForLongPress implements Runnable { private int mOriginalWindowAttachCount; public void run() { if (isPressed() && (mParent != null) && mOriginalWindowAttachCount == mWindowAttachCount) { if (performLongClick()) { mHasPerformedLongPress = true; } } }
能够看到。当用户按下,首先会设置标识为PREPRESSED
假设115后,没有抬起,会将View的标识设置为PRESSED且去掉PREPRESSED标识,然后发出一个检測长按的延迟任务,延时为:ViewConfiguration.getLongPressTimeout() - delayOffset(500ms -115ms),这个115ms刚好时检測额PREPRESSED时间;也就是用户从DOWN触发開始算起,假设500ms内没有抬起则觉得触发了长按事件:
1、假设此时设置了长按的回调,则运行长按时的回调。且假设长按的回调返回true;才把mHasPerformedLongPress置为ture;
2、否则,假设没有设置长按回调或者长按回调返回的是false;则mHasPerformedLongPress依旧是false;
好了DOWN就分析完毕了;大家回个神,以下回到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行推断当然触摸点有没有移出我们的View,假设移出了:
1、运行removeTapCallback();
2、然后推断是否包括PRESSED标识,假设包括。移除长按的检查:removeLongPressCallback();
3、最后把mPrivateFlags中PRESSED标识去除,刷新背景。
private void removeTapCallback() { if (mPendingCheckForTap != null) { mPrivateFlags &= ~PREPRESSED; removeCallbacks(mPendingCheckForTap); } }这个是移除,DOWN触发时设置的PREPRESSED的检測。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;
假设115ms后,你才移出控件外,则你的当前mPrivateFlags一定为PRESSED且发送了长按的检測;
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我们也分析完毕了,总结一下:仅仅要用户移出了我们的控件:则将mPrivateFlags取出PRESSED标识,且移除全部在DOWN中设置的检測,长按等;
以下再回个神,回到View的onTouchEvent的ACTION_UP:
3、MotionEvent.ACTION_UP
26到69行:
27行:推断mPrivateFlags是否包括PREPRESSED
28行:假设包括PRESSED或者PREPRESSED则进入运行体,也就是无论是115ms内或者之后抬起都会进入运行体。
36行:假设mHasPerformedLongPress没有被运行,进入IF
38行:removeLongPressCallback()。移除长按的检測
45-50行:假设mPerformClick假设mPerformClick为null,初始化一个实例,然后马上通过handler加入到消息队列尾部,假设加入失败则直接运行 performClick();加入成功,在mPerformClick的run方法中就是运行performClick();
最终运行了我们的click事件了,以下看一下performClick()方法:
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:假设prepressed为true,进入IF体:
为mPrivateFlags设置表示为PRESSED,刷新背景,125毫秒后运行mUnsetPressedState
否则:mUnsetPressedState.run();马上运行;也就是无论咋样,最后mUnsetPressedState.run()都会运行;
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(),假设mPendingCheckForTap不为null,移除;
4、总结
好了。代码跨度还是相当大的,以下须要总结下:
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的推断,假设OnTouchListener不为null且返回true。则表示事件被消费,onTouchEvent不会被运行;否则运行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、假设115ms内没有触发UP,则将标志置为PRESSED,清除PREPRESSED标志,同一时候发出一个延时为500-115ms的,检測长按任务消息;
c、假设500ms内(从DOWN触发開始算)。则会触发LongClickListener:
此时假设LongClickListener不为null,则会运行回调。同一时候假设LongClickListener.onClick返回true,才把mHasPerformedLongPress设置为true;否则mHasPerformedLongPress依旧为false;
MOVE时:
主要就是检測用户是否划出控件。假设划出了:
115ms内,直接移除mPendingCheckForTap;
115ms后,则将标志中的PRESSED去除,同一时候移除长按的检查:removeLongPressCallback();
UP时:
a、假设115ms内。触发UP,此时标志为PREPRESSED,则运行UnsetPressedState。setPressed(false);会把setPress转发下去,能够在View中复写dispatchSetPressed方法接收;
b、假设是115ms-500ms间,即长按还未发生,则首先移除长按检測,运行onClick回调;
c、假设是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事件依旧能够触发;d、最后运行mUnsetPressedState.run()。将setPressed传递下去,然后将PRESSED标识去除;
最后问个问题,然后再运行个样例结束:
1、setOnLongClickListener和setOnClickListener是否仅仅能运行一个
不是的,仅仅要setOnLongClickListener中的onClick返回false,则两个都会运行;返回true则会屏幕setOnClickListener
最后我们给MyButton同一时候设置setOnClickListener和setOnLongClickListener,运行看看:
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, "onTouch ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onTouch ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "onTouch ACTION_UP"); break; default: break; } return false; } }); mButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Toast.makeText(getApplicationContext(), "onclick",Toast.LENGTH_SHORT).show(); } }); mButton.setOnLongClickListener(new OnLongClickListener() { @Override public boolean onLongClick(View v) { Toast.makeText(getApplicationContext(), "setOnLongClickListener",Toast.LENGTH_SHORT).show(); return false; } }); } }效果图:
能够看到LongClickListener已经ClickListener都触发了~
最后。本篇博文完毕了对View的事件分发机制的整个流程的说明,而且对源代码进行了分析;
当然了。View结束,肯定到我们的ViewGroup了。请点击:Android ViewGroup事件分发机制