View事件分发（传递）机制
前言：View事件分发机制是Android中比较重要和复杂的部分，只有理解了事件分发，才能更好的自定义控件和解决滑动冲突，本篇文章基于API25（7.1）。
相关方法
- public boolean disptachTouchEvent(MotionEvent ev)
事件分发方法，触控事件从该方法开始传递，返回true表示分发完成，返回false则失败
- public boolean onInterceptTouchEvent(MotionEvent ev)
事件拦截方法，只有ViewGroup中才存在，在dispatchTouchEvent中判断是否拦截事件由自己处理，或者交给子View（ViewGroup）分发，返回true表示拦截事件，默认返回false
- public boolean onTouchEvent(MotionEvent ev)
事件处理方法，处理事件，返回true表示消耗事件，返回false表示不消耗事件
| dispatchTouchEvent | OnInterceptTouchEvent | onTouchEvent | |
|---|---|---|---|
| Activity | √ | × | √ |
| ViewGroup | √ | √ | √ |
| View | √ | × | √ |
源码分析
Activity
/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
/**
* Retrieve the current {@link android.view.Window} for the activity.
* This can be used to directly access parts of the Window API that
* are not available through Activity/Screen.
*
* @return Window The current window, or null if the activity is not
* visual.
*/
public Window getWindow() {
return mWindow;
}
事件首先从Activity的disptachTouchEvent的方法开始调用，调用了Window的superDispatchTouchEvent方法，至于事件MotionEvent的来源不在本章讨论的范围内
/**
* Called when a touch screen event was not handled by any of the views
* under it. This is most useful to process touch events that happen
* outside of your window bounds, where there is no view to receive it.
*
* @param event The touch screen event being processed.
*
* @return Return true if you have consumed the event, false if you haven't.
* The default implementation always returns false.
*/
public boolean onTouchEvent(MotionEvent event) {
if (mWindow.shouldCloseOnTouch(this, event)) {
finish();
return true;
}
return false;
}
Activity默认不会消耗事件
Window
可以看到这是个抽象方法，Window是一个抽象类，Window的唯一实现是PhoneWindow
/**
* Abstract base class for a top-level window look and behavior policy. An
* instance of this class should be used as the top-level view added to the
* window manager. It provides standard UI policies such as a background, title
* area, default key processing, etc.
*
* The only existing implementation of this abstract class is
* android.view.PhoneWindow, which you should instantiate when needing a
* Window.
*/
public abstract class Window {
...
/**
* Used by custom windows, such as Dialog, to pass the touch screen event
* further down the view hierarchy. Application developers should
* not need to implement or call this.
*
*/
public abstract boolean superDispatchTouchEvent(MotionEvent event);
...
}
PhoneWindow
// 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);
}
PhoneWindow的该方法代码就一行，调用了DecorView的superDisptachTouchEvent方法
DecorView
/** @hide */
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
...
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
...
}
DecorView调用了父类FrameLayout的disptachTouchEvent，FrameLayout继承于ViewGroup，且没有重写该方法，所以终于到了ViewGroup的dispatchTouchEvent方法，下面开始重点
ViewGroup
ViewGroup的dispatchTouchEvent方法比较长，先分开看
dispatchTouchEvent#1
// 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();
}
// Check for interception.
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;
}
首先在ACTION_DOWN中清除所有的触摸状态和目标, 然后检查是否需要拦截事件，当为ACTION_DOWN事件，首选检查标志位FLAG_DISALLOW_INTERCEPT是否已设置，即是否不拦截事件，通过requestDisallowInterceptTouchEvent方法可以设置该标志位，默认没有设置，disallowIntercept是false，如果已设置该标志位，则不截断子View（ViewGroup)事件，否则会调用自身的onInterceptTouchEvent方法。
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
// We're already in this state, assume our ancestors are too
return;
}
if (disallowIntercept) {
mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
} else {
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
// Pass it up to our parent
if (mParent != null) {
mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
}
}
/**
* @param ev The motion event being dispatched down the hierarchy.
* @return Return true to steal motion events from the children and have
* them dispatched to this ViewGroup through onTouchEvent().
* The current target will receive an ACTION_CANCEL event, and no further
* messages will be delivered here.
*/
public boolean onInterceptTouchEvent(MotionEvent ev) {
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;
}
可以看到ViewGroup默认情况是不会拦截事件，所以接下来遍历子View，并调用disptachTransformedTouchEvent
dispatchTouchEvent#2
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
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);
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 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);
...
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;
}
...
}
}
如果有符合条件的child（触摸点和变换后的点在该View内）对应于dispatchTransformedTouchEvent返回true的，则newTouchTraget = addTouchTarget(child, idBitsToAssign)会走到
/**
* Adds a touch target for specified child to the beginning of the list.
* Assumes the target child is not already present.
*/
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
可以看到如果mFirstTouchTarget赋值了，则后续事件序列继续走进第一步事件拦截判断语句内，否则后续的事件序列都由该ViewGroup拦截
/**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
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;
}
// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
// If for some reason we ended up in an inconsistent state where it looks like we
// might produce a motion event with no pointers in it, then drop the event.
if (newPointerIdBits == 0) {
return false;
}
// If the number of pointers is the same and we don't need to perform any fancy
// irreversible transformations, then we can reuse the motion event for this
// dispatch as long as we are careful to revert any changes we make.
// Otherwise we need to make a copy.
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
// Perform any necessary transformations and dispatch.
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;
}
可以看到如果child为null则会调用ViewGroup父类的dispatchTouchEvent,ViewGroup的父类是View则会走到View的dispatchTouchEvent中；否则会调用child的dispatchTouchEvent，即事件继续传递下去
disptachTouchEvent#3
// Dispatch to touch targets.
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;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
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;
}
}
所以如果mFirstTouchTarget为null，即ViewGroup拦截事件或者ViewGroup没有child消耗该事件，则调用super#disptachTouchEvent否则调用child的dispatchTouchEvent,如果child不消耗ACTION_DOWN除外的事件，则该事件消失，不会回传给父ViewGroup，最终会传给Activity的onTouchEvent，并且后续的事情此child也能收到。如果ViewGroup在ACTION_MOVE中拦截事件，则会走到dispatch(ev,true,target.child,target.pointIdBits)中，在该方法中child会收到一个ACTION_CANCEL事件，VieGroup不处理该事件，且predecessor == null，mFirstTouchTarget = next 最终，mFirstTouchTarget置为null，从下个事件开始都交由ViewGroup处理。
View
/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
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;
}
首先会检查是否该View会设置OnTouchListener、是否enable、onTouchListener.onTouch(this,event)是否返回true，如果条件都满足则标识该View消耗了事件，传递完成，否则会继续调用onTouchEvent
/**
* Implement this method to handle touch screen motion events.
*
* If this method is used to detect click actions, it is recommended that
* the actions be performed by implementing and calling
* {@link #performClick()}. This will ensure consistent system behavior,
* including:
*
* - obeying click sound preferences
*
- dispatching OnClickListener calls
*
- handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
* accessibility features are enabled
*
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
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;
}
如果控件不是enable的，但是是可以点击的clickable、longClickable或者contextClickable的也会消耗该事件；如果控件是enable的，则会根据事件的时间长短来执行checkForLongClick或者perfomrClick方法,可点击的View的onTouchEvent默认返回true，如Button，不可点击的则返回false，如TextView和ImageView
private void checkForLongClick(int delayOffset, float x, float y) {
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
mHasPerformedLongPress = false;
if (mPendingCheckForLongPress == null) {
mPendingCheckForLongPress = new CheckForLongPress();
}
mPendingCheckForLongPress.setAnchor(x, y);
mPendingCheckForLongPress.rememberWindowAttachCount();
postDelayed(mPendingCheckForLongPress,
ViewConfiguration.getLongPressTimeout() - delayOffset);
}
}
private final class CheckForLongPress implements Runnable {
private int mOriginalWindowAttachCount;
private float mX;
private float mY;
@Override
public void run() {
if (isPressed() && (mParent != null)
&& mOriginalWindowAttachCount == mWindowAttachCount) {
if (performLongClick(mX, mY)) {
mHasPerformedLongPress = true;
}
}
}
public void setAnchor(float x, float y) {
mX = x;
mY = y;
}
public void rememberWindowAttachCount() {
mOriginalWindowAttachCount = mWindowAttachCount;
}
}
/**
* Calls this view's OnLongClickListener, if it is defined. Invokes the
* context menu if the OnLongClickListener did not consume the event,
* anchoring it to an (x,y) coordinate.
*
* @param x x coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @param y y coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @return {@code true} if one of the above receivers consumed the event,
* {@code false} otherwise
*/
public boolean performLongClick(float x, float y) {
mLongClickX = x;
mLongClickY = y;
final boolean handled = performLongClick();
mLongClickX = Float.NaN;
mLongClickY = Float.NaN;
return handled;
}
/**
* Calls this view's OnLongClickListener, if it is defined. Invokes the
* context menu if the OnLongClickListener did not consume the event.
*
* @return {@code true} if one of the above receivers consumed the event,
* {@code false} otherwise
*/
public boolean performLongClick() {
return performLongClickInternal(mLongClickX, mLongClickY);
}
/**
* Calls this view's OnLongClickListener, if it is defined. Invokes the
* context menu if the OnLongClickListener did not consume the event,
* optionally anchoring it to an (x,y) coordinate.
*
* @param x x coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @param y y coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @return {@code true} if one of the above receivers consumed the event,
* {@code false} otherwise
*/
private boolean performLongClickInternal(float x, float y) {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_LONG_CLICKED);
boolean handled = false;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnLongClickListener != null) {
handled = li.mOnLongClickListener.onLongClick(View.this);
}
if (!handled) {
final boolean isAnchored = !Float.isNaN(x) && !Float.isNaN(y);
handled = isAnchored ? showContextMenu(x, y) : showContextMenu();
}
if (handled) {
performHapticFeedback(HapticFeedbackConstants.LONG_PRESS);
}
return handled;
}
/**
* Call this view's OnClickListener, if it is defined. Performs all normal
* actions associated with clicking: reporting accessibility event, playing
* a sound, etc.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
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;
}
结论
View事件传递.png
- Activity和View中没有OnInterceptTouchEvent方法，只有ViewGroup才有
- 分发过程由上到下，Activity->Window(PhoneWindow)->DecorView->ViewGroup->View,处理过程由下到上，View->ViewGroup->DecorView->Window(PhoneWindow)->Activity,如果分发（处理）过程中有View/ViewGroup消耗事件[返回true]则事件不会往下传递（往上传递）
- 事件分发序列是有一个ACTION_DOWN，零或多个ACTION_MOVE，单个ACTION_UP组成,即ACTION_DOWN->[ACTION_MOVE->...->ACTION_MOVE->]ACTION_UP
- ViewGroup的ACTION_DOWN事件必定调用OnInterceptTouchEvent，如果拦截了ACTION_DOWN事件则后续的事件序列都不会再调用OnInterceptTouchEvent, 事件都由该ViewGroup处理，ViewGroup的Child也不会再收到后续的事件序列
- 如果ViewGroup在ACTION_MOVE中拦截事件，则会走到dispatch(ev,true,target.child,target.pointIdBits)中，在该方法中child会收到一个ACTION_CANCEL事件，ViewGroup不处理该事件，最终，mFirstTouchTarget置为null，从下个事件开始都交由ViewGroup处理
- 子类可以通过调用的父类的requestDisallowInterceptTouchEvent来改变父类是否拦截事件，但是如果ACTION_DOWN事件已被父类拦截，则无法改变;且ACTION_DOWN事件不受该方法标志位FLAG_DISALLOW_INTERCEPT控制，因为ViewGroup的disptachTouchEvent方法在收到ACTION_DOWN事件时会调用resetTouchState方法重置该标志位
- 如果child不消耗ACTION_DOWN,即dispatchTouchEvent返回false，则后续的事件序列都由其父ViewGroup处理，调用View#dispatchTouchEvent
- 如果child不消耗ACTION_DOWN除外的事件，则该事件消失，不会回传给父ViewGroup，最终会传给Activity的onTouchEvent，但是后续的事情此child也能收到
- View#disptachTouchEvent中首先会判断是否有设置OnTouchListener、控件enable且onTouch返回true，满足条件则事件分发完成，否则会继续调用View#onTouchEvent
- View#onTouchEvent中，即使该View不是enable的，但是其是clickable、longClickable或者contextClickable的则也消耗事件，如果View是enable的，则根据时间判断是执行performClick还是performLongClick，可点击的View的onTouchEvent默认返回true，如Button，不可点击的则返回false，如TextView和ImageView
- View方法调用顺序: dispatchTouchEvent->mOnTouchListener#onTouch->onTouchEvent->performLongClick->performClick
- ViewGroup拦截ACTION_DOWN:dispatchTouchEvent->onInterceptTouchEvent->super.disptachTouchEvent，后续事件： dispatchTouchEvent->super.disptachTouchEvent
- ViewGroup不拦截ACTION_DOWN： child消耗ACTION_DOWN, dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->,后续事件事件dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->;child不消耗ACTION_DOWN，dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->super.disptachTouchEvent，后续事件
dispatchTouchEvent->super.disptachTouchEvent - ViewGroup拦截ACTION_MOVE： dispatchTouchEvent->onInterceptTouchEvent->child#dispatchTouchEvent(ACTION_CANCEL),后续事件disptachTouchEvent->super.dispatchTouchEvent
参考文献
- Android事件分发机制完全解析，带你从源码的角度彻底理解(上) ,
Android事件分发机制完全解析，带你从源码的角度彻底理解(下) - 图解 Android 事件分发机制
- 十分钟彻底弄明白 View 事件分发机制
- Android View事件分发机制源码分析
- Android事件传递机制
- View 的事件分发机制
- 安卓自定义View进阶-事件分发机制原理,安卓自定义View进阶-事件分发机制详解
- Activity, Window, PhoneWindow,ViewGroup,View,MotionEvent
- 《Android开发艺术探索》第三章View事件分发机制