紧接上一篇对ViewGroup点击事件分发机制源码的分析。接下来我跟着一同学习View对点击事件的处理机制源码分析。好废话不多说直接找到View的 dispatchTouchEvent 方法，如下所示：
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;
}
通过这几天的学习，渐渐找到了看源码的关键位置，大致看一下整个方法设置了一个变量 result 它用来标识接收事件的 view 是否消耗了当前事件。所以我们只需要关注改变 'result' 变量的几个位置和该方法调用 return 语句的地方即可以大致掌握整个方法的语义了。 所以我们的重点是下面这段代码：
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;
首先下面这段代码是判断接收事件的 view 是否可用并判断是否为鼠标滚动或拖动，如果是鼠标的滚动和拖动直接消耗事件return true退出方法。这里并不是我们关心的重点。
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
再往下看，新建了一个内部类 ListenerInfo 的对象li，该类是负责监控和管理该view绑定了哪些Lisntener。重点关注这段代码：
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
可以发现如果该view设置了 OnTouchListener 事件就会优先调用 onTouch() 方法，这里就证实了 OnTouchListener 的优先级高于 onTouchEvent，这样做的好处就是方便在外界处理点击事件。
接下来就看见了 onTouchEvent() 方法的调用，我们继续分析这个方法的源码。
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;
}
又是一个超长的方法，淡定淡定，慢慢来首先看下最上面，通过这段代码的注释我们接了解了，如果当前view处于不可用状态依然会消耗这个事件，只是不会有任何回应。
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);
}
接着，如果View设置了代理，那么会执行 TouchDelegate 的onTouchEvent()方法
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
关于代理类 TouchDelegate感觉也非常有趣，从官网得到了该类的介绍。
Helper class to handle situations where you want a view to have a larger touch area than its actual view bounds. The view whose touch area is changed is called the delegate view. This class should be used by an ancestor of the delegate. To use a TouchDelegate, first create an instance that specifies the bounds that should be mapped to the delegate and the delegate view itself.
通过简单的翻译，知道它可以扩大一个View的接收点击事件的区域并不改变View本身的大小。设置时需要在该View的祖先控件设置代理。感觉是不是非常有趣的类，具体使用方法这里提供一个其他作者书写的demo,请各位同学自行查阅吧。
好继续分析代码，接下来可以看到只要该View的 CLICKABLE和LONG_CLICKABLE只要有一个为true即可消耗该事件。这也同样证明了View能否消耗点击事件与它是否为DISABLE状态没有关系。
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
接下来就进入ACTION_UP的事件下，会看到它会执行performClick()该方法内部会调用OnClickListener的onClick()方法，简单点说，当事件为ACTION_UP时，如果该View设置了OnClickListener就会调用它的onClick()方法。代码如下：
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();
}
}
}
performClick()方法的代码如下：
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;
}
以上就是关于View处理点击事件的源码分析，通过源码分析我们已经对第一篇所罗列的结论进行了一一证明，有兴趣的同学可以看一下第一篇博文最后所罗列的关于点击事件机制的一些结论。通过三篇文章使我自己对点击事件的机制有了更深刻的认识，虽然我的理解还很肤浅，但我知道只要继续保持不断的思考，我们都会成为更好的自己。
