事件分发
ViewRootImpl/DecorView/Activity/Window/DecorView
事件由 ViewRootImpl 分发，会先分发到 DecorView。
//ViewRootImpl.java
private int processPointerEvent(QueuedInputEvent q) {
final MotionEvent event = (MotionEvent)q.mEvent;
...
//关键点：mView分发Touch事件，mView就是DecorView
boolean handled = mView.dispatchPointerEvent(event);
maybeUpdatePointerIcon(event);
maybeUpdateTooltip(event);
...
} // View.java
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
//分发Touch事件
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}//FrameLayout
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Window.Callback cb = mWindow.getCallback();
return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
}Window.Callback都被Activity和Dialog实现，所以变量cb可能就是Activity和Dialog。
Activity
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}Window
// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}DecorView
//extends ViewGroup
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks{
public boolean superDispatchTouchEvent(MotionEvent event) {
//调用 ViewGroup 的 dispatchTouchEvent
return super.dispatchTouchEvent(event);
}
}ViewGroup
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//....
boolean handled = false;
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 如果是 down 事件，清除之前状态
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();
}
// 检查是否需要拦截
final boolean intercepted;
//如果是down事件或者前面事件已经有子view接收，需要重新判断是否需要拦截
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
//拦截没有被禁用时，需要调用 onInterceptTouchEvent 判断
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
//禁用了拦截，直接返回false
intercepted = false;
}
} else {
//不是down事件，并且也没有其他子view处理过之前的事件
//则ViewGroup自己拦截处理
intercepted = true;
}
// 检查是否取消
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
TouchTarget newTouchTarget = null;
//是否已由新目标处理事件
boolean alreadyDispatchedToNewTouchTarget = false;
//....
if (!canceled && !intercepted) {
//只针对这三种事件寻找View，其他情况一律由之前的目标处理
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
//按照z轴坐标以及自定义绘制顺序（如果有的话）排列子view
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
//获取view在列表中的索引
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
//检查事件发生位置是否在View内以及View是否可以接受事件
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//此时找到了事件发生在区域内且可以接收事件的view
//在 touchTarget 链表中寻找 View对应的TouchTarget
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
//view 已经在接受事件了
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
//没有找到对应target，先分发事件给 view
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// View 的 dispatchTouchEvent 返回了true
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// 找到在mChildren中的真实索引
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
//添加新的TouchTarget
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}//end for
if (preorderedList != null) preorderedList.clear();
}//end if
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;
}
}//end if
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
//调用父类的 dispatchToucheEvent
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;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
//Down 事件时走到这里
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//其他事件走到这里
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;
}//end while
}//end else
}//end if
return handled;
}View
public boolean dispatchTouchEvent(MotionEvent event) {
boolean result = false;
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
//设置了onTouchListener/enable/onTouch返回true
//直接返回
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
return result;
}onTouchEvent(event) 中会调用onClick 和 onLongClick。
调用onClick 是在UP事件时，检查是否clickable以及是否设置监听；
调用onLongClick 是在Down 事件时，发出一个延时任务，如果任务执行时还是按下状态，就执行难onLongClick.
//todo 源码
多点触控
处理POINTER_DOWN 和POINTER_UP，进行指针处理。
区分 actionIndex(pointerIndex)/ pointerId.
滑动冲突
父View根据需要重写 onIntercept 或者子View根据需要调用父View的requestDisallowIntercept禁用父View对事件的拦截。
requestDisallowIntercept 会向上传递。
相关问题
事件传递大体过程：Activity--> Window-->DecorView --> View树从上往下，传递过程中谁想拦截就拦截自己处理。MotionEvent是Android中的点击事件。主要事件类型：
ACTION_DOWN 手机初次触摸到屏幕事件
ACTION_MOVE 手机在屏幕上滑动时触发，会回调多次
ACTION_UP 手指离开屏幕时触发
需要关注的几个方法。
dispatchTouchEvent(event);
onInterceptTouchEvent(event);
onTouchEvent(event);
上面3个方法可以用以下伪代码来表示其关系：
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean consume = false;//事件是否被消费
if (onInterceptTouchEvent(ev)) {//调用onInterceptTouchEvent判断是否拦截事件
consume = onTouchEvent(ev);//如果拦截则调用自身的onTouchEvent方法
} else {
consume = child.dispatchTouchEvent(ev);//不拦截调用子View的dispatchTouchEvent方法
}
return consume;//返回值表示事件是否被消费，true事件终止，false调用父View的onTouchEvent方法
}如何解决View的滑动冲突？
父类根据需要重写 onIntercept 或者子View根据需要调用requestDisallowIntercept
onTouch()、onTouchEvent()和onClick()关系？
如果一个View需要处理事件，它设置了OnTouchListener，那么OnTouchListener的onTouch方法会被回调。如果onTouch返回false,则onTouchEvent会被调用，反之不会。在onTouchEvent方法中，事件为Action.UP的时候会回调OnClickListener的onClick方法，可见OnClickListener的优先级很低。
防止短时间内重复点击
通过在对比两次ACTION_DOWN事件之间的时间间隔是否小于最小间隔，如果小于直接忽略。
视应用范围，这段逻辑可以放在View/ViewGroup/Activity 中 。
private static final long CLICK_DURATION = 900;
//上次 ACTION_DOWN 事件发生时间
private long lastDownTime = 0;
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
boolean ignore = event.getDownTime() - lastDownTime < CLICK_DURATION;
lastDownTime = event.getDownTime();
if (ignore) {
return false;
}
}
return super.dispatchTouchEvent(event);
}相关链接
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