前言
最近在看View的事件分发阅读源码，并做笔记。内容以注释的形式插入在代码中，请仔细阅读文章中给出的源码。文章内容都是作者自己的理解，或有错漏之处，请见谅。
一、代码构建
1.1 自定义Button
为了能看见事件调用什么方法，我们继承Button类重载了dispatchTouchEvent()和onTouchEvent()。而所有发送给View的事件，首先是由dispatchTouchEvent()接收。
public class MyButton extends Button {
private static final String TAG = "MyButton";
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
@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);
}
}
1.2 xml布局
在main_activity.xml中使用自定义的Button
<RelativeLayout
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">
<com.corevk.demoproject.MyButton
android:id="@+id/MyButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</RelativeLayout>
1.3 MainActivity
绑定按钮并给按钮设置一个监听器OnTouchListener。后面我会说明这个监听器的用途。
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private Button mButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mButton = (Button) findViewById(R.id.MyButton);
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; // 返回值会影响事件的分发行为
}
});
}
}
1.4 梳理
通过上面的源码，我们一共设置了三个东西，一个dispatchTouchEvent()，一个onTouchEvent()和一个OnTouchListener()。
这三个被重写的方法都对ACTION_DOWN、ACTION_MOVE、ACTION_UP的动作显示信息。
二、运行结果
2.1 OnTouchListener false
如果手指一直在屏幕上滑动，Log的ACTION_DOWN和ACTION_UP之间会报告很多ACTION_MOVE的信息。
View.OnTouchListener中返回false，点击按钮马上放开。结果按照dispatchTouchEvent -> onTouch -> onTouchEvent出现
10-13 23:53:29.382 17840-17840/? E/MyButton: dispatchTouchEvent ACTION_DOWN
10-13 23:53:29.382 17840-17840/? E/MainActivity: onTouch ACTION_DOWN
10-13 23:53:29.382 17840-17840/? E/MyButton: onTouchEvent ACTION_DOWN
10-13 23:53:29.414 17840-17840/? E/MyButton: dispatchTouchEvent ACTION_UP
10-13 23:53:29.414 17840-17840/? E/MainActivity: onTouch ACTION_UP
10-13 23:53:29.414 17840-17840/? E/MyButton: onTouchEvent ACTION_UP
2.2 OnTouchListener true
在View.OnTouchListener的返回值中返回true，点击按钮马上放开:dispatchTouchEvent（） -> onTouch
10-13 23:55:32.523 18106-18106/? E/MyButton: dispatchTouchEvent ACTION_DOWN
10-13 23:55:32.523 18106-18106/? E/MainActivity: onTouch ACTION_DOWN
10-13 23:55:32.554 18106-18106/? E/MyButton: dispatchTouchEvent ACTION_UP
10-13 23:55:32.554 18106-18106/? E/MainActivity: onTouch ACTION_UP
当View.OnTouchListener的返回值中返回true，onTouchEvent()不会触发，说明事件没有分发到onTouchEvent()。
三、源码分析
3.1 dispatchTouchEvent
先来看dispatchTouchEvent()源码
public boolean dispatchTouchEvent(MotionEvent event) {
if (event.isTargetAccessibilityFocus()) {
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
event.setTargetAccessibilityFocus(false);
}
// 默认为false
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
stopNestedScroll(); // 停止嵌套滚动
}
// 用安全机制来过滤触摸事件：true为继续分发，false终止分发
// 具体实现是去判断是否被其它窗口遮挡住了，如果遮挡住就要过滤该事件
if (onFilterTouchEventForSecurity(event)) {
// 这里获取mListenerInfo
ListenerInfo li = mListenerInfo;
// 以下所有条件成立执行这个语句块并返回True:
// 1. 若ListenerInfo存在，mListenerInfo不为空
// 2. mOnTouchListener不为空，设置了OnTouchListener监听器
// 3. view为enable
// 4. mOnTouchListener.onTouch(this, event)返回true
if (li != null
&& li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)){
result = true; // 已经消费事件返回True
}
// 若OnTouchListener返回true，事件会被OnTouchListener消费
// 否则交给onTouchEven处理，然后返回True
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
那么li.mOnTouchListener值在哪里设定？上面的代码有一段可以知道：
ListenerInfo li = mListenerInfo;
if (li != null
&& li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
li.mOnTouchListener是依赖mButton.setOnTouchListener的。如果不调用mButton.setOnTouchListener，li.mOnTouchListener为null。
当我们在MainActivity - onCreate中给mButton.setOnTouchListener创建一个View.OnTouchListener()实例的同时，这个实例会被保存在getListenerInfo().mOnTouchListener。
public void setOnTouchListener(OnTouchListener l) {
getListenerInfo().mOnTouchListener = l;
}
而getListenInfo里面判断mListenerInfo是否为空，非空直接返回，否则创建新的ListenerInfo。
ListenerInfo getListenerInfo() {
if (mListenerInfo != null) {
return mListenerInfo;
}
mListenerInfo = new ListenerInfo();
return mListenerInfo;
}
3.2 onTouchEvent
如果设置了View.OnTouchListener()，其返回值决定了事件是否继续分发给onTouchEvent实例。假如onTouchEvent可以接收事件，那后面又会做什么？
public boolean onTouchEvent(MotionEvent event) {
// 获取动作时间中点击屏幕的位置
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
// 获取操作
final int action = event.getAction();
// View是Disable就执行这个代码块
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP
&& (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// 无效但可以点击或长按的View是可以消费点击事件的，只是没有响应
return (((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
// 有mTouchDelegate就会把事件交给代理处理，返回true
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
// 如果view是可点击的，就处理不同的点击操作，完成后返回true。
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
// 分支的代码分析在后面，对不同操作代码做了分割剖析
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) {
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
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);
}
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;
}
// 只要是可点击的，处理完后返回true
return true;
}
// 什么都没做就返回false，事件继续下发
return false;
}
四、MotionEvent详解
在Android的触摸消息中有三种监测：
- prepressed：用户轻触(tap)屏幕，触摸时间小于TAP_TIMEOUT
- pressed：用户点击(press)屏幕，触摸时间大于TAP_TIMEOUT，介于TAP_TIMEOUT和LONG_PRESS_TIMEOUT之间
- long pressed：用户长按(long press)屏幕，时间大于DEFAULT_LONG_PRESS_TIMEOUT或LONG_PRESS_TIMEOUT
不同版本的Android API时间值可能不同，现在API 23(Android 6.0)TAP_TIMEOUT是100ms，旧版本是115ms，我们按照最新值解说。
/**
* Defines the duration in milliseconds of the pressed state in child
* components.
*/
private static final int PRESSED_STATE_DURATION = 64;
/**
* Defines the duration in milliseconds we will wait to see if a touch event
* is a tap or a scroll. If the user does not move within this interval, it is
* considered to be a tap.
*/
private static final int TAP_TIMEOUT = 100;
/**
* Defines the default duration in milliseconds before a press turns into
* a long press
*/
private static final int DEFAULT_LONG_PRESS_TIMEOUT = 500;
4.1 MotionEvent.ACTION_DOWN
// 长按事件默认为false;
mHasPerformedLongPress = false;
if (performButtonActionOnTouchDown(event)) {
break;
}
// 检查是否在滚动容器中
boolean isInScrollingContainer = isInScrollingContainer();
// Views是否在可滚动的视图中，这会推迟点击的反馈
if (isInScrollingContainer) {
// 增加PREPRESSED标志
mPrivateFlags |= PFLAG_PREPRESSED;
// 创建CheckForTap()实例 mPendingCheckForTap
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
// 延迟100ms后执行是是否达到PRESSED状态
// 当处于可滚动视图内，则延迟TAP_TIMEOUT，再反馈按压状态
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// 不在可滚动容器的情况下马上设置PRESSED
setPressed(true, x, y);
// 马上开始检测长按动作
checkForLongClick(0);
}
在上面的代码中，调用时先经过100ms的延时，再使用CheckForTap
private final class CheckForTap implements Runnable {
// 记录了点击的坐标
public float x;
public float y;
@Override
public void run() {
// 取消PFLAG_PREPRESSED标志
mPrivateFlags &= ~PFLAG_PREPRESSED;
// 先检查点击位置是否移动
// 没有移动就对PRESSED做操作，增加PRESSED标志
setPressed(true, x, y);
// 检查长按动作
checkForLongClick(ViewConfiguration.getTapTimeout());
}
}
checkForLongClick
// 调用处传入delayOffset = 100ms
private void checkForLongClick(int delayOffset) {
// 仅在view支持长按时执行，否则直接结束方法
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
mHasPerformedLongPress = false;
if (mPendingCheckForLongPress == null) {
mPendingCheckForLongPress = new CheckForLongPress();
}
mPendingCheckForLongPress.rememberWindowAttachCount();
// 因为调用这个方法之前已经延迟100ms，所以需要减去100ms
postDelayed(mPendingCheckForLongPress,
ViewConfiguration.getLongPressTimeout() - delayOffset);
}
}
CheckForLongPress
private final class CheckForLongPress implements Runnable {
private int mOriginalWindowAttachCount;
@Override
public void run() {
// 需要检查是否已经到达PRESSED状态
if (isPressed() && (mParent != null)
&& mOriginalWindowAttachCount == mWindowAttachCount) {
// 仅在performLongClick()返回true时mHasPerformedLongPress为true
if (performLongClick()) {
mHasPerformedLongPress = true;
}
}
}
public void rememberWindowAttachCount() {
mOriginalWindowAttachCount = mWindowAttachCount;
}
}
在run里面调用的performLongClick
如果设置了长按回调，那么回调会在下面得到调用。返回值与handled相同。这样就直接控制了mHasPerformedLongPress。
public boolean performLongClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_LONG_CLICKED);
boolean handled = false;
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnLongClickListener != null) {
handled = li.mOnLongClickListener.onLongClick(View.this);
}
if (!handled) {
handled = showContextMenu();
}
if (handled) {
performHapticFeedback(HapticFeedbackConstants.LONG_PRESS);
}
return handled;
}
4.2 MotionEvent.ACTION_MOVE
// 当前位置x,y
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
// 移动到按钮的范围外就会执行
if (!pointInView(x, y, mTouchSlop)) {
// 在按钮外，移除PREPRESSED状态和对应回调
removeTapCallback();
// 如果是PRESSED，就移除长按检测，并移除PRESSED状态
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
removeLongPressCallback();
setPressed(false);
}
}
public void setPressed(boolean pressed) {
// 如果状态不是PRESSED，更新标志位并刷新背景
final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED);
if (pressed) {
mPrivateFlags |= PFLAG_PRESSED;
} else {
mPrivateFlags &= ~PFLAG_PRESSED;
}
if (needsRefresh) {
refreshDrawableState();
}
dispatchSetPressed(pressed);
}
当触发时间不到100ms，触点移到控件外，就会清除PREPRESSED标志。
private void removeTapCallback() {
if (mPendingCheckForTap != null) {
mPrivateFlags &= ~PFLAG_PREPRESSED;
removeCallbacks(mPendingCheckForTap);
}
}
时间大于100ms就会开始长按检测。如果已经出发长按检测，就需要把长按检测移除。
private void removeLongPressCallback() {
if (mPendingCheckForLongPress != null) {
removeCallbacks(mPendingCheckForLongPress);
}
}
4.3 MotionEvent.ACTION_UP
// 判断mPrivateFlags是否包含PREPRESSED
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
// PRESSED或PREPRESSED有一个就执行
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);
}
// 没有长按且不忽略下一个抬起事件，就移除长按
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.
// 创建PerformClick实例
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
// 通过handler添加到消息队列尾部，失败就直接执行performClick()
if (!post(mPerformClick)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
// PRESSED_STATE_DURATION = 64
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
performClick是在ACTION_UP的过程中被调用的，onClick事件是在这里被执行的。
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;
}
private final class UnsetPressedState implements Runnable {
@Override
public void run() {
setPressed(false);
}
}
