定义
将点击事件传递到某个view&处理的整个过程。
事件分发顺序
Activity -> ViewGroup -> View
事件分发的方法
- dispatchTouchEvent()，分发（传递）事件。
- onInterceptTouchEvent()，判断是否拦截事件（只存在viewGroup，普通的view没有此事件）。
- onTouchEvent()，处理点击事件。
onInterceptTouchEvent()和onTouchEvent()都在dispatchTouchEvent()中调用
简述
当点击的时候，首先调用viewgroup的dispatchTouchEvent，如果顶级的viewgroup拦截了此事件（onInterceptTouchEvent返回true），则此事件交给顶级的viewgroup进行处理。如果不拦截则交给子view进行处理，如果子view不进行处理则再返回父级进行处理，依次向上推。
View的事件调度顺序
onTouchListener > onTouchEvent > onLongClickListener > onClickListener
ACTION_DOWN事件会从Activity-ViewGroup-View-ViewGroup的顺序一直查看是否消费了onTouchEvent事件，如下
I/System.out: Activity dispatchTouchEvent ----> 0
I/System.out: ViewGroup dispatchTouchEvent ----> 0
I/System.out: ViewGroup onInterceptTouchEvent ----> 0
I/System.out: View dispatchTouchEvent ----> 0
I/System.out: View onTouchEvent ----> 0
I/System.out: ViewGroup onTouchEvent ----> 0
ACTION_UP,ACTION_MOVE,ACTION_CANCEL则会在消费了事件的View直接传给onTouchEvent结束事件，如下
I/System.out: Activity dispatchTouchEvent ----> 1
I/System.out: ViewGroup dispatchTouchEvent ----> 1
I/System.out: ViewGroup onTouchEvent ----> 1
ViewGroup的dispatchTouchEvent源码分析
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//验证事件是否连续
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
//判断事件是否是针对可访问的焦点视图(应该是屏幕辅助功能)
// If the event targets the accessibility focused view and this is it, start
// normal event dispatch. Maybe a descendant is what will handle the click.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
//事件是否被处理完
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
//如果事件发生的View在的窗口，没有被遮挡
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
//判断是不是Down事件，如果是的话，就要做初始化操作
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 清除之前所有的状态
// 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();
}
//是否拦截事件
// Check for interception.
final boolean intercepted;
//如果当前是Down事件，或者已经有处理Touch事件的目标了
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//判断允不允许这个View拦截
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
//允许拦截事件
intercepted = onInterceptTouchEvent(ev);//判断是不是拦截了
//重新恢复Action，以免action在上面的步骤被人为地改变了
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
//如果说，事件已经初始化过了，并且没有子View被分配处理，那么就说明，这个ViewGroup已经拦截了这个事件
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
// 判断事件是否是针对可访问的焦点视图
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
//检查事件是否被取消了
//如果viewFlag被设置了PFLAG_CANCEL_NEXT_UP_EVENT ,那么就表示，下一步应该是Cancel事件
//或者如果当前的Action为取消，那么当前事件应该就是取消了。
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
//如果需要（不是取消，也没有被拦截）的话，那么在触摸down事件的时候更新触摸目标列表
//split代表，当前的ViewGroup是不是支持分割MotionEvent到不同的View当中
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
//新的触摸对象
TouchTarget newTouchTarget = null;
//是否把事件分配给了新的触摸
boolean alreadyDispatchedToNewTouchTarget = false;
//事件不是取消事件，也没有拦截那么就要判断
if (!canceled && !intercepted) {
// 如果事件是针对可访问性焦点视图，我们将其提供给具有可访问性焦点的视图。
// 如果它不处理它，我们清除该标志并像往常一样将事件分派给所有的 ChildView。
// 我们检测并避免保持这种状态，因为这些事非常罕见
// 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;
//如果是个全新的Down事件
//或者是有新的触摸点
//或者是光标来回移动事件（不太明白什么时候发生）
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
//这个事件的索引，也就是第几个事件，如果是down事件就是0
final int actionIndex = ev.getActionIndex(); // always 0 for down
//获取分配的ID的bit数量
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// 清除此指针ID的早期触摸目标，防止不同步。
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
//如果新的触摸对象为null并且当前ViewGroup有子元素
if (newTouchTarget == null && childrenCount != 0) {
// 获取触摸位置坐标
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
//找到可以接收这个事件的子元素
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList preorderedList = buildTouchDispatchChildList();
//是否使用自定义的顺序来添加控件
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//从最后向前扫描 主要能找到最新加入的view
for (int i = childrenCount - 1; i >= 0; i--) {
//如果是用了自定义的顺序来添加控件，那么绘制的View的顺序和mChildren的顺序是不一样的
//所以要根据getChildDrawingOrder取出真正的绘制的View
//自定义的绘制，可能第一个会画到第三个，和第四个，第二个画到第一个，这样里面的内容和Children是不一样的
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// 如果有一个视图具有可访问性焦点，我们希望它首先获取事件，
// 如果不处理，我们将执行正常的分派。
// 尽管这可能会分发两次，但它能保证在给定的时间内更安全的执行。
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
// 检查View是否允许接受事件(即处于显示状态(VISIBLE)或者正在播放动画)
// 或者 检查触摸位置是否在View区域内
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//获取新的触摸对象，如果当前的子View在之前的触摸目标的列表当中就返回touchTarget
newTouchTarget = getTouchTarget(child);
//子View不在之前的触摸目标列表那么就返回null
if (newTouchTarget != null) {
//如果新的触摸目标对象不为空，那么就把这个触摸的ID赋予它，这样子，
//这个触摸的目标对象的id就含有了好几个pointer的ID了
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;// ChildView 已经准备好接受在其区域内的事件。
break;
}
//如果子View不在之前的触摸目标列表中，先重置childView的标志，去除掉CACEL的标志
resetCancelNextUpFlag(child);
//调用子View的dispatchTouchEvent,并且把pointer的id 赋予进去
//如果说，子View接收并且处理了这个事件，那么就更新上一次触摸事件的信息，
//并且为创建一个新的触摸目标对象，并且绑定这个子View和Pointer的ID
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
//找到原始索引
// 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;
}
//可访问性焦点没有处理事件
//对所有child进行分发
// 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();
}
// 没有找到 ChildView 接收事件
// 将指针交给最近添加的目标
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;
}
}
}
// 子视图未消耗Touch Event 或者 被拦截未向子视图派发Touch Event
// 分发 TouchTarget
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
// 没有 TouchTarget，在当前 ViewGroup 处理。
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// 分发TouchTarget，如果我们已经分发过，则避免分配给新的目标。
// 如有必要，取消分发。
// 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;
//遍历TouchTargt树.分发事件，如果我们已经分发给了新的TouchTarget那么我们就不再分发给newTouchTarget
while (target != null) {
final TouchTarget next = target.next;
//已将将事件分配给了新的触摸
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
//是否让child取消处理事件，如果为true，就会分发给child一个ACTION_CANCEL事件
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//分发事件
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
//cancelChild也就是说，派发给了当前child一个ACTION_CANCEL事件，
//那么就移除这个child
if (cancelChild) {
//没有父节点，也就是当前是第一个TouchTarget
//那么就把头去掉
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
//把下一个赋予父节点的上一个，这样当前节点就被丢弃了
predecessor.next = next;
}
//回收内存
target.recycle();
//把下一个赋予现在
target = next;
//下面的两行不执行了，因为我们已经做了链表的操作了。
//主要是我们不能执行predecessor=target，因为删除本节点的话，父节点还是父节点
continue;
}
}
//如果没有删除本节点，那么下一轮父节点就是当前节点，下一个节点也是下一轮的当前节点
predecessor = target;
target = next;
}
}
//遇到了取消事件、或者是单点触摸下情况下手指离开，我们就要更新触摸的状态或取消
// 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) {
//如果是多点触摸下的手指抬起事件，就要根据idBit从TouchTarget中移除掉对应的Pointer(触摸点)
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
整体逻辑
- DOWN事件进来，清空状态
- 为intercepted赋值，判断是否拦截
- 不拦截则从ChildView中找到可以接收事件的ChildView
- 判断ChildView是否处理了事件，mFirstTouchTarget为空，表示不管是down还是其他事件没有ChildView要处理在当前 ViewGroup 处理；否则，该事件序列已经有孩子处理了