1、点击事件在到达Activity后，会从dispatchTouchEvent(MotionEvent ev)方法中进行分发
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
2、getWindow()为PhoneWindow，所以随后会进入PhoneWindow中。
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
3、mDecor为DecorView，所以后面进入DecorView中的superDispatchTouchEvent(MotionEvent event)方法中。
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
4、DecorView的父类是FrameLayout，而FrameLayout中并没有重写该方法，所以会进入ViewGroup 的dispatchTouchEvent(MotionEvent ev)方法中，正式开始进入事件的分发流程。
该部分比较长也比较复杂，可分为三部分：
- 判断该ViewGroup是否拦截事件
- 获取ViewGroup的子View(或者是ViewGroup)列表，并进行遍历，判断是否有child会拦截事件。
- 最后开始分发或者处理事件。
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
...此处删掉许多代码...
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 如果收到的是ACTION_DOWN事件，进行一些复位或者说是初始化工作。
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();
}
// 第一个步骤，检查次ViewGroup是否会拦截事件，如果拦截事件，intercepted赋值为true，否则为false
final boolean intercepted;
// ACTION_DOWN事件才会进行处理 2022/2/24
if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) {
//判断该事件是否要拦截，默认为false
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 {
intercepted = true;
}
...此处删掉许多代码...
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
// 如果ViewGroup不拦截，则在其child中进行事件分发 2022/2/24
// If the event is targeting accessibility focus we give it to the
// view that has accessibility focus and if it does not handle it
// we clear the flag and dispatch the event to all children as usual.
// We are looking up the accessibility focused host to avoid keeping
// state since these events are very rare.
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
// 只有为ACTION_DOWN事件时，才进行分发 2022/2/24
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
//每一个事件都会有一个索引
final int actionIndex = ev.getActionIndex(); // always 0 for down
//每一个事件都会有一个唯一标识
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
// childrenCount表示该ViewGroup下面的子View数量 2022/2/24
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x =
isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);
final float y =
isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
// buildTouchDispatchChildList用于对这些子View进行一个排序 2022/2/24
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
// 在该循环中，将事件分发到child中进行是否拦截并处理的判断。
// 倒序取出，排在后面的先被分发事件 2022/2/24
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// 判断child能够接收事件 2022/2/24
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
// 在dispatchTransformedTouchEvent方法中判断该Child是否拦截并处理事件 2022/2/24
// 如果当前child拦截事件，则返回true，如果不拦截，则返回false 2022/2/24
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// 如果该View处理该事件，则中断循环 2022/2/24
// 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();
// 如果拦截事件，为newTouchTarget赋值 2022/2/24
newTouchTarget = addTouchTarget(child, idBitsToAssign);
// 设置标识，已经进行了分发 2022/2/24
alreadyDispatchedToNewTouchTarget = true;
break;
}else{
// 如果当前View不处理，则继续循环。 2022/2/24
}
// 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();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// 不管在上面的循环中是否有child拦截该事件，都会走到下面的流程，然后根据根据是当前ViewGroup拦截事件还是在Child中拦截事件进行不同的处理。 2022/2/24
// 分发或者处理 ，mFirstTouchTarget 默认为null，如果在上面的循环中有child拦截了事件，则会被赋值。 2022/2/24
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
// 进行事件处理，handled标识是否已经处理，true表示已经处理 2022/2/24
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// 表示在上面的循环中，有child拦截了事件 2022/2/24
// 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;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
// 后面的ACTION_MOVE事件会通过该处进行分发 2022/2/24
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;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
补充：
通过如下方法列出ViewGroup中的child列表，并进行一个排序，通过Z值对View进行排序
ArrayList<View> buildOrderedChildList() {
final int childrenCount = mChildrenCount;
if (childrenCount <= 1 || !hasChildWithZ()) return null;
if (mPreSortedChildren == null) {
mPreSortedChildren = new ArrayList<>(childrenCount);
} else {
// callers should clear, so clear shouldn't be necessary, but for safety...
mPreSortedChildren.clear();
mPreSortedChildren.ensureCapacity(childrenCount);
}
final boolean customOrder = isChildrenDrawingOrderEnabled();
for (int i = 0; i < childrenCount; i++) {
// add next child (in child order) to end of list
final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
final View nextChild = mChildren[childIndex];
final float currentZ = nextChild.getZ();
// insert ahead of any Views with greater Z
int insertIndex = i;
// Z值越大，排序越靠前。 2022/2/24
while(insertIndex>0 && mPreSortedChildren.get(insertIndex-1).getZ() > currentZ) {
insertIndex--;
}
mPreSortedChildren.add(insertIndex, nextChild);
}
return mPreSortedChildren;
}
判断child能够接收事件时，也有两个方法关注
方法1：根据View是否可见以及是否有动画，来判断是否可以处理事件
protected boolean canReceivePointerEvents() {
// 判断View是否可以接收事件 -> View是否可见，如果不可见的话，是否有动画 2022/2/24
return (mViewFlags & VISIBILITY_MASK) == VISIBLE || getAnimation() != null;
}
方法2：判断触发事件的位置，是否在此View 的绘制范围内。如果不在View范围内，不能拦截事件。
@UnsupportedAppUsage
protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
final float[] point = getTempLocationF();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}
5、不管ViewGroup是否拦截事件，以及是否有child拦截事件，最后都会进入dispatchTransformedTouchEvent方法
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case. We don't need to perform any transformations
// or filtering. The important part is the action, not the contents.
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
...此处省略不少代码...
// Perform any necessary transformations and dispatch.
if (child == null) {
// 如果child为null，直接调用View中的dispatchTouchEvent 2022/2/24
// 如果处理事件，则返回true，如果不处理事件，则返回false 2022/2/24
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());
}
// 如果child不为空，则调用传入的child 的dispatchTouchEvent方法，如果child重写了该方法，
// 调用重写的dispatchTouchEvent方法，如果该child没有重写该方法，会调用其父类的dispatchTouchEvent方法 2022/2/24
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
进入该方法时：
- 如果有child拦截事件，则此方法的第三个入参即为拦截事件的View（或者是ViewGroup）对象，则进入该View（或者是ViewGroup）的dispatchTouchEvent方法中继续处理，如果是ViewGroup，则可能又是以上的流程。
- 如果没有child拦截事件，则此方法的第三个入参为null，则进入super.dispatchTouchEvent方法中进行处理，而ViewGroup 的super为View，如果可以处理，返回true，如果不处理，返回false，结束该流程。
补充：
View中的dispatchTouchEvent方法：
public boolean dispatchTouchEvent(MotionEvent event) {
...此处删除不少代码...
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;
}
}
...此处删除不少代码...
return result;
}
可以看到，当事件分发到View中时，会首先进行mOnTouchListener事件的处理，如果没有注册OnTouchListener事件，或者在此事件中返回了false，则会继续进入onTouchEvent(event)中进行处理。
在onTouchEvent方法中，performClickInternal()方法中
public boolean onTouchEvent(MotionEvent event) {
...次数删除不少代码...
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
...次数删除不少代码...
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
...次数删除不少代码...
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) {
...次数删除不少代码...
if (!post(mPerformClick)) {
performClickInternal();
}
}
}
...次数删除不少代码...
}
return true;
}
return false;
}
最终会进入到performClick方法中，在这里，会处理我们最熟悉的onClickListener事件。
public boolean performClick() {
...此处删除不少代码...
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
...此处删除不少代码...
return result;
}
