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.

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";
public MyButton(Context context) {
super(context);
} public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
} public MyButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
} @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);
} @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);
} }
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button; public class MainActivity extends AppCompatActivity { private Button mButton;
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mButton = (Button) findViewById(R.id.btn);
mButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "onClick");
}
});
mButton.setOnTouchListener(new View.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;
}
});
}
}
<?xml version="1.0" encoding="utf-8"?>
<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"
android:gravity="center"
tools:context="com.jcf.eventanalysis.MainActivity"> <com.loaerman.eventanalysis.MyButton
android:id="@+id/btn"
android:layout_width="200dp"
android:layout_height="100dp"
android:text="MyButton"/>
</LinearLayout>

日志打印:

因为手没抖动,所以没有触发MOVE,手抖可能会打印一堆MOVE的日志

可以看到:DOWN,MOVE,UP都会按照下面的顺序执行:

1、dispatchTouchEvent

2、setOnTouchListener的onTouch

3、onTouchEvent


源码分析

View的dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
} boolean result = false; if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
} final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
} if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
} if (!result && onTouchEvent(event)) {
result = true;
}
} if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
} // Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
} return result;
}

可以看到: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


setOnTouchListener

public void setOnTouchListener(OnTouchListener l) {
getListenerInfo().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。

View的onTouchEvent

public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction(); if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// 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)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
} if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_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 (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
} if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// 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) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
} removeTapCallback();
}
mIgnoreNextUpEvent = false;
break; case MotionEvent.ACTION_DOWN:
mHasPerformedLongPress = false; if (performButtonActionOnTouchDown(event)) {
break;
} // Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer(); // For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break; case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break; case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y); // Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback(); setPressed(false);
}
}
break;
} return true;
} return false;
}

代码中如果当前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;

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;

if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// 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)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}

接下来到我们的重点了:

下面代码可以判断: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) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {....}

switch (event.getAction())

判断事件类型,DOWN,MOVE,UP等;

case MotionEvent.ACTION_DOWN

case MotionEvent.ACTION_DOWN:
mHasPerformedLongPress = false; if (performButtonActionOnTouchDown(event)) {
break;
} // Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer(); // For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break;

给mPrivateFlags设置一个PREPRESSED的标识:

mPrivateFlags |= PFLAG_PREPRESSED;

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

mHasPerformedLongPress = false;

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:

postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());

1、ViewConfiguration.getTapTimeout()为100毫秒;

2、CheckForTap

private final class CheckForTap implements Runnable {
public float x;
public float y; @Override
public void run() {
mPrivateFlags &= ~PFLAG_PREPRESSED;
setPressed(true, x, y);
checkForLongClick(ViewConfiguration.getTapTimeout(), x, y);
}
}

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;

private void checkForLongClick(int delayOffset, float x, float y) {
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
mHasPerformedLongPress = false; if (mPendingCheckForLongPress == null) {
mPendingCheckForLongPress = new CheckForLongPress();
}
mPendingCheckForLongPress.setAnchor(x, y);
mPendingCheckForLongPress.rememberWindowAttachCount();
postDelayed(mPendingCheckForLongPress,
ViewConfiguration.getLongPressTimeout() - delayOffset);
}
}
private final class CheckForLongPress implements Runnable {
private int mOriginalWindowAttachCount;
private float mX;
private float mY; @Override
public void run() {
if (isPressed() && (mParent != null)
&& mOriginalWindowAttachCount == mWindowAttachCount) {
if (performLongClick(mX, mY)) {
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100ms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;

MotionEvent.ACTION_MOVE

case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y); // Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback(); setPressed(false);
}
}
break;

首先拿到当前触摸的x,y坐标;

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();

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

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;

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100ms时,你就已经移出控件外了;

如果100ms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;

总结: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;

MotionEvent.ACTION_UP

case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_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 (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
} if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// 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) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
} removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;

判断mPrivateFlags是否包含PREPRESSED

boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;

如果包含PRESSED或者PREPRESSED则进入执行体,也就是无论是100ms内或者之后抬起都会进入执行体。

如果mHasPerformedLongPress没有被执行,进入IF

removeLongPressCallback();移除长按的检测

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,先看一下performClick()方法:

public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
} sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}

这就是用户的mOnClickListener的调用

如果prepressed为true,进入IF体:

为mPrivateFlags设置表示为PRESSED,刷新背景,64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 {
@Override
public void run() {
setPressed(false);
}
}
public void setPressed(boolean pressed) {
final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED); if (pressed) {
mPrivateFlags |= PFLAG_PRESSED;
} else {
mPrivateFlags &= ~PFLAG_PRESSED;
} if (needsRefresh) {
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;


总结:

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100ms后的mPendingCheckForTap;

b、如果100ms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500-100ms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:

100ms内,直接移除mPendingCheckForTap;

100ms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100ms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100ms-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;


问题:

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,就可以看到LongClickListener和ClickListener都会触发

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