上篇分析过了view的dispatchTouchEvent的源码的具体流程。
首先介绍下view被点击的三个状态
1、PrePress (姑且叫为预按)，这个状态是我们的view被加入到一个scrolling view中才会存在。具体的意义是，举个简单的例子，当我们将手放在listView的一item上的时候，由于当前还不知道用户是要点击item还是想滑动listview，所以先将view设为PrePress状态；
2、Press状态，用户将手放到view上面，如果不是1的状态，就里面设置为Press状态。那么先进入了PrePress，那么将会触发一个检测，也即CheckForTap()，默认时间是100ms，如果超过了100ms，将由PrePress进入到Press状态；
3、LongPress状态，这个状态由Press状态过度过来，如果用户在一个view上停留超过一定的时间（默认为500ms），将进入该状态。
话不多说，现在分析一下源码
/** 实施此方法来处理触摸屏幕动作事件。
* Implement this method to handle touch screen motion events.
* <p>
* If this method is used to detect click actions, it is recommended that
* the actions be performed by implementing and calling
* {@link #performClick()}. This will ensure consistent system behavior,
* including:
* <ul>
* <li>obeying click sound preferences
* <li>dispatching OnClickListener calls
* <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
* accessibility features are enabled
* </ul>
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
// 获取动作点击屏幕的位置坐标
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
// 获取手势动作
//如果当前View是一个DISABLED状态，且当前View是一个可点击或者是可长按的状态 则clickable返回true。表示当前事件在此消耗且不做处理
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
//如果当前View状态为DISABLED
if ((viewFlags & ENABLED_MASK) == DISABLED) {
//如果View的状态是被按压过，且当抬起事件产生，重置View状态为未按压，刷新Drawable的状态
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return clickable;
}
// 如果设置了触摸代理
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
//就交给mTouchDelegate.onTouchEvent处理，如果返回true，则事件被处理了，则不会向下传递
return true;
}
}
//如果当前View的状态是可点击或者是可长按的，就对事件流进行细节处理
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
//如果是抬起的手势
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
//清除各种状态
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
//prepressed指的是，如果view包裹在一个scrolling View中，可能会进行滑动处理，所以设置了一个prePress的状态
//大致是等待一定时间，然后没有被父类拦截了事件，则认为是点击到了当前的view,从而显示点击态
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
//如果是pressed状态或者是prepressed状态，才进行处理
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
//如果设定了获取焦点，那么调用requestFocus获得焦点
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
//在释放之前给用户显示View的prepressed的状态，状态需要改变为PRESSED，并且需要将背景变为按下的状态为了让用户感知到
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);
}
// 是否处理过长按操作了，如果是，则直接返回
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
//如果不是长按的话，仅仅是一个Tap，所以移除长按的回调
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.
//UI子线程去执行click，为了让click事件开始的时候其他视觉发生变化不影响。
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
//如果post消息失败，直接调用处理click事件
if (!post(mPerformClick)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
//ViewConfiguration.getPressedStateDuration() 获得的是按下效果显示的时间,由PRESSED_STATE_DURATION常量指定,在2.2中为125毫秒,也就是隔了125毫秒按钮的状态重置为未点击之前的状态。目的是让用户感知到click的效果
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
//如果通过post(Runnable runnable)方式调用失败，则直接调用
// If the post failed, unpress right now
mUnsetPressedState.run();
}
//移除Tap的回调 重置View的状态
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
//如果是按下的手势
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
//在触摸事件中执行按钮相关的动作,如果返回true则表示已经消耗了down
mHasPerformedLongPress = false;
if (!clickable) {
//仅在View支持长按时执行有效，否则直接退出方法
checkForLongClick(0, x, y);
break;
}
//这个performButtonActionOnTouchDown(event) 一般的设备都是返回false.因为目前的实现中,它是处理如鼠标的右键的.(如果此View响应或者其父View响应右键菜单,那么就此事件就被消耗掉了.)
if (performButtonActionOnTouchDown(event)) {
break;
}
// 判断当前view是否是在滚动器当中
// 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;
//将view的状态变为PREPRESSED，检测是Tap还是长按事件
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
//如果是在滚动器当中，在滚动器当中的话延迟返回事件，延迟时间为 ViewConfiguration.getTapTimeout()=100毫秒
//在给定的tapTimeout时间之内,用户的触摸没有移动,就当作用户是想点击,而不是滑动.
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;
//接收到系统发出的ACTION_CANCLE事件时，重置状态， 将所有的状态设置为最初始
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
//如果是移动的手势
case MotionEvent.ACTION_MOVE:
if (clickable) {
//将实时位置传递给背景（前景）图片
drawableHotspotChanged(x, y);
}
// Be lenient about moving outside of buttons
// 判断当前滑动事件是否还在当前view当中，不是就执行下面的方法
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
// 移除PREPRESSED状态和对应回调
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// 是PRESSED就移除长按检测，并移除PRESSED状态
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
}
return true;
}
return false;
}
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