所谓事件分发,就是对MotionEvent的分发过程,当一个MotionEvent产生了以后,系统需要把这个事件传递给一个具体的View,而这个传递的过程就是分发过程。引用一个《Android开发艺术探索》里的概念:
同一个事件序列是指手指接触屏幕的那一刻起,到手指离开屏幕的那一刻结束,在这个工程中所产生的一系列事件,这个事件序列以down事件开始,中间含有数量不定的move事件,最终以up事件结束。
一个事件产生之后,先由Activity处理,activity交给window来处理
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
window又交给了mDecor处理
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
mDecor是一个继承了FrameLayout的对象,它会调用ViewGroup的dispatchTouchEvent,真正干活的是ViewGroup同学
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
下面来看看这位同学
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
ACTION_DOWN的时候把上一个事件序列修改的变量置为默认状态,包括重置子控件通过requestDisallowInterceptTouchEvent方法设置的不让父控件拦截它的状态。
// intercepted代表父控件是否拦截事件,true代表拦截,false不拦截。
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
满足actionMasked == MotionEvent.ACTION_DOWN和mFirstTouchTarget != null的其中一个条件时才会计算intercepted的值,不然直接就是true。mFirstTouchTarget != null代表父控件没有拦截事件,子控件处理消耗了事件。所以在整个事件序列里如果子控件没有在刚开始的ACTION_DOWN中消耗事件就是返回true的话,以后就没有机会再处理事件了。
事件序列的以一个ACTION_DOWN开始,所以会进入if里,disallowIntercept的值代表子控件是否告诉了ViewGroup不拦截事件,但是上面已经清除了这个状态,所以这里一定为false,所以intercepted的值取决于onInterceptTouchEvent,onInterceptTouchEvent的默认值是false。
public boolean onInterceptTouchEvent(MotionEvent ev) {
// 这里是鼠标相关
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
return false;
}
如果ViewGroup要处理事件,需要重写这个方法,而且如果子控件没有在ACTION_DOWN中消耗事件的话,mFirstTouchTarget != null不成立,在整个事件序列的其他事件中,ViewGroup不再判断onInterceptTouchEvent,直接拦截事件,子控件再也收不到事件 。
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// 省略代码
// 标记一
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
// 省略代码
// 标记二
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
标记一处。canViewReceivePointerEvents用来判断是否正在播放动画,isTransformedTouchPointInView用来判断点击事件的坐标是否落在子元素的区域内。满足条件处理事件,不满足遍历下一个子控件。
标记二处。调用dispatchTransformedTouchEvent方法。主要在这里
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// 省略代码
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
如果child不为空,调用child的dispatchTouchEvent方法,child继续分发事件。
如果child为空,调用super.dispatchTouchEvent,自己处理事件。
这里child不为空,事件交给了child去处理,如果child消耗了事件返回了true,mFirstTouchTarget被赋值。
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
可以看出TouchTarget是一个链表格式的类,返回mFirstTouchTarget,赋值给newTouchTarget,循环结束。
// 标记三
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
// 标记四
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
// 标记五
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
标记三处,mFirstTouchTarget == null有三种情况
其一,ViewGroup没有子控件
其二,ViewGroup拦截子控件
其三,事件分发给了子控件,子控件没有消耗事件,返回了false
上面dispatchTransformedTouchEvent返回true,子控件消耗了事件的话,执行标记四。之后事件序列的其他事件除了不需要再去循环遍历children,直接执行标记五处的dispatchTransformedTouchEvent。
ViewGroup就结束了,下面看View。
ViewGroup在分发事件的时候会分发给View的dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent event) {
// 省略代码
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;
}
}
// 省略代码
return result;
}
View的dispatchTouchEvent比较简单,handleScrollBarDragging主要是鼠标的处理,返回false。所以是否执行onTouchEvent取决于onTouch的返回结果。
如果设置了mOnTouchListener并且返回值为true,直接返回结果,然后当前MotionEvent就结束了,接着处理下一个MotionEvent,onClick,onLongClick都没机会执行了。
如果不设置mOnTouchListener或者onTouch的返回值为false,接着执行onTouchEvent
public boolean onTouchEvent(MotionEvent event) {
// 省略
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
if ((viewFlags & ENABLED_MASK) == DISABLED) {
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;
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
// 省略
}
view的LONG_CLICKABLE默认为false,部分view的CLICKABLE为true,部分view的的CLICKABLE为false。当setOnClickListener或者setOnLongClickListener的时候,都会先置为true。
如果view是DISABLED的,直接返回,如果clickable为ture,即使DISABLED也会消耗事件。
如果有设置代理,处理代理。
如果clickable为true,onTouchEvent返回值默认true,clickable为false,不作处理,返回值false。
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
// 省略代码
boolean isInScrollingContainer = isInScrollingContainer();
if (isInScrollingContainer) {
// 设置为PFLAG_PREPRESSED状态,代表按下之前的状态
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
// 延迟发送一个CheckForTap,CheckForTap负责将状态再重置回来,然后再发送一个长按的延迟事件
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// 直接发送一个延时的长按事件,如果在延迟时间内没有被取消,则回调onLongClick
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
ACTION_DOWN里判断是否在一个可滚动的ViewGroup里,这里会递归判断所有的ViewGroup。
如果在一个可滚动的ViewGroup里,延迟发送一个CheckForTap,CheckForTap负责将状态再重置回来,然后再发送一个长按的延迟事件。不在可滚动的ViewGroup,直接发送一个延时的长按事件,如果在延迟时间内没有被取消,则回调onLongClick。setPressed用来处理view的状态,按下,需不需要重绘。
onLongClick的默认处理时间是500毫秒。
private static final int DEFAULT_LONG_PRESS_TIMEOUT = 500;
case MotionEvent.ACTION_MOVE:
// 省略
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
ACTION_MOVE比较简单,如果事件在控件范围外,移除所有延迟消息。
case MotionEvent.ACTION_UP:
// 如果mPrivateFlags不为0,预按下或者按下状态
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// 如果允许获取焦点,并且当前没有获取到焦点
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
// 获取焦点
focusTaken = requestFocus();
}
if (prepressed) {
// 置为按下状态,重绘
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// 如果长按没有触发,说明是点击事件,移除长按
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// 在这里回调onClick事件
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
// 用来设置view不同状态下的背景
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();
}
// 移除点击
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
ACTION_UP比较长,用注释的方式解释了。主要是判断长按事件有没有回调,没有说明不到500毫秒,移除长按,回调onClick事件,设置view不同状态下的背景。事件就结束了。
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
ACTION_CANCEL,系统控制,取消所有回调,重置所有状态。
onTouchEvent执行结束,默认返回true消耗事件,然后返回到ViewGroup的dispatchTouchEvent,层层返回,最后回到activity的dispatchTouchEvent中。
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
一般情况下getWindow().superDispatchTouchEvent(ev)都为true,事件结束了。如果所有的view都没有消耗事件,最后由Activity的onTouchEvent处理。