- 触摸事件都被封装为MotionEvent
- 触摸事件有：
- ACTION_DOWN
- ACTION_UP
- ACTION_MOVE
- ACTION_POINTER_DOWN
- ACTION_POINTER_UP
- ACTION_CANCEL
- 每个MotionEvent包含
- 触摸位置
- 触点数量
- 事件时间戳
- 一个“手势Gesture”是以ACTION_DOWN开始，以ACTION_UP结束。
事件的分发处理：
- 开始于Activity的dispatchTouchEvent()
- 分发到ViewGroup，ViewGroup可以进行截获
- ViewGroup分发到子View
- 要处理事件，必须对事件的ACTION_DOWN声明为感兴趣。
- 事件处理，结束于处理事件的View；事件未处理，结束于Activity的onTouchEvent。
最初的事件，来源于Activity。是Activity::dispatchTouchEvent。
另外还有:
Activity::dispatchKeyEvent(KeyEvent event)
Activity::dispatchTrackballEvent(MotionEvent ev)
Activity::dispatchGenericMotionEvent(MotionEvent ev)
等等
// Activity源码
/**
* 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);
}
/**
* Called whenever a key, touch, or trackball event is dispatched to the
* activity. Implement this method if you wish to know that the user has
* interacted with the device in some way while your activity is running.
*／
public void onUserInteraction() {
}
private Window mWindow;
public Window getWindow() {
return mWindow;
}
final void attach(........) {
mWindow = new PhoneWindow(this, window, activityConfigCallback);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
if (mParent != null) {
mWindow.setContainer(mParent.getWindow());
}
mWindowManager = mWindow.getWindowManager();
mCurrentConfig = config;
mWindow.setColorMode(info.colorMode);
}
上面可以看到：
Activity::dispatchTouchEvent里面对事件进行分发，可以重写这个方法，截获所有触摸事件，使得没有任何事件可以分发到Window／ViewGroup／View，是所有事件的入口。
分发顺序是：Activity -> Window -> ViewGroup -> ... ViewGroup -> View。
ACTION_DOWN是一次新的事件的开始，所以会特别对待。ViewGroup和View里面在收到ACTION_DOWN事件时，会重置自身的触摸状态，重新开始计数。
仅当Activity里面的ViewGroup／View都没有消化事件，才能执行到Activity自身的onTouchEvent事件。
onUserInteraction是用户与Activity交互的回调，只要用户与Activity有交互，就会触发。表示用户触发了任意事件。
Activity里面的Window实例是
PhoneWindow，所以superDispatchTouchEvent调用的PhoneWindow::superDispatchTouchEvent().
PhoneWindow源码
/frameworks/base/core/java/com/android/internal/policy/PhoneWindow.java
@Override
public boolean superDispatchKeyEvent(KeyEvent event) {
return mDecor.superDispatchKeyEvent(event);
}
@Override
public boolean superDispatchKeyShortcutEvent(KeyEvent event) {
return mDecor.superDispatchKeyShortcutEvent(event);
}
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
@Override
public boolean superDispatchTrackballEvent(MotionEvent event) {
return mDecor.superDispatchTrackballEvent(event);
}
@Override
public boolean superDispatchGenericMotionEvent(MotionEvent event) {
return mDecor.superDispatchGenericMotionEvent(event);
}
// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
mDecor = generateDecor(-1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);
}
}
上面可以看到：
PhoneWindow::superDispatchTouchEvent()调用的是mDecor::superDispatchTouchEvent().
mDecor是
DecorView，是Window的rootview。DecorView继承于FrameLayout.所以最终superDispatchTouchEvent会调用到
DecorView::superDispatchTouchEvent.也即是，Activity里接受到的事件，最先会分发到
DecorView（当然，你可以重写方法，使其分发到自己的View).
DecorView源码
/frameworks/base/core/java/com/android/internal/policy/DecorView.java
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
public boolean superDispatchKeyEvent(KeyEvent event) {
// Give priority to closing action modes if applicable.
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
final int action = event.getAction();
// Back cancels action modes first.
if (mPrimaryActionMode != null) {
if (action == KeyEvent.ACTION_UP) {
mPrimaryActionMode.finish();
}
return true;
}
}
return super.dispatchKeyEvent(event);
}
public boolean superDispatchKeyShortcutEvent(KeyEvent event) {
return super.dispatchKeyShortcutEvent(event);
}
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
public boolean superDispatchTrackballEvent(MotionEvent event) {
return super.dispatchTrackballEvent(event);
}
public boolean superDispatchGenericMotionEvent(MotionEvent event) {
return super.dispatchGenericMotionEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
return onInterceptTouchEvent(event);
}
}
最后还是调用到父类FrameLayout::dispatchTouchEvent
FrameLayout源码
/frameworks/base/core/java/android/widget/FrameLayout.java
public class FrameLayout extends ViewGroup {
}
FrameLayout没有dispatchTouchEvent方法，意味着FrameLayout没有覆盖ViewGroup::dispatchTouchEvent。所以，最终调用到ViewGroup::dispatchTouchEvent
ViewGroup源码
/frameworks/base/core/java/android/view/ViewGroup.java
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// 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);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
/// ACTION_DOWN表示一次新事件，进行了状态的清理
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);
/// 这个方法会向TouchTarget链表分发ACTION_CANCEL.
resetTouchState();
/// 这个方法会设置mFirstTouchTarget为null。
}
// Check for interception.
/// 截获仅发生在ACTION_DOWN，或 mFirstTouchTarget不为空才进行截获（mFirstTouchTarget是指当前事件最先处理的子对象）
/// ACTION_DOWN是初次事件，所以直接进入onInterceptTouchEvent()；
/// mFirstTouchTarget不为空，1.可能是POINTER_DOWN/MOVE/UP等非初次事件且有子对象。
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
/// 能进入这里，说明：1.是ACTION_DOWN初次事件，不管有没有子对象 2.是其它POINTER_DOWN/MOVE/UP事件且当前ViewGroup有子对象。
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
/// 如果没有禁止截获，则调用onInterceptTouchEvent，也即是说onInterceptTouchEvent并不是无条件执行，还需要启用截获。
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.
/// 既不是事件的开始（DOWN事件表示事件开始），又没有可以接受事件的子对象（mFirstTouchTarget==null）则认为事件无需再往下分发。
/// 无需往下分发，等价于当前ViewGroup截获了事件。所以设置intercepted为true。
///（其实还是有点本质区别，这里只是没有子对象可以接受事件，并不是ViewGroup主动截获。可以叫这种情况为叶子）
intercepted = true;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
/// 这里截获为true有两种情况：
/// 1. this.onInterceptTouchEvent 返回true。
/// 2. 非DOWN事件且没有子对象。
/// 所以，这里能调用，只有1情况下发生，即主动截获。
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
/// 上面整个过程都没有return，说明会继续执行。
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
/// 既非取消事件，也非叶子，且没有主动截获才能执行。（如果是叶子，无需往这个代码块看）
if (!canceled && !intercepted) {
// If the event is targeting accessiiblity 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.
/// 如果事件目标是有焦点的，那么将事件分发给焦点View，否则清除flag，按照正常逻辑分发。
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
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.
/// 根据坐标点，查找ViewGroup里面可以处理这个点的Children Views，从前往后查找。
final ArrayList preorderedList = buildOrderedChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
/// isChildrenDrawingOrderEnabled可以指定child的绘制顺序。通过重写getChildDrawingOrder。
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : I;
/// 重写getChildDrawingOrder可以改变ViewGroup绘制child的顺序。
final View child = (preorderedList == null)
? children[childIndex] : preorderedList.get(childIndex);
// 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.
/// 如果有一个child获取了焦点，那么先让它获得事件，遍历找到那个获取了焦点的child。
/// 如果没有焦点，则进行普通的遍历分发，看哪个child能够处理事件。
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
/// 1. 有焦点，找到了获取焦点的child。没焦点，child是当前遍历的child。
/// 当前child是否能够接受点事件，点是否在当前View里面。不是，查找下一个。
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
/// 找到了点所在，可以接收事件的child view。中断查找！！！（意思是，ViewGroup里面仅能有一个子View能够处理事件）
/// 从TouchTarget链表里查找当前child view，找到，说明DOWN事件时，child view返回了true，接收了这次事件。
/// 所以紧随的POINTER_DOWN／MOVE／UP事件就直接分发到该child view即可。所以退出遍历。
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.
// child已经表明接收事件，所以将新的信息发给它处理。
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
/// 如果从TouchTarget链表中找不到当前child view，则表示，这次事件是新的事件（可能是新的DOWN事件）。
/// 如果这个child view准备分发Up事件，先取消了Up事件分发的标识（因为有新的事件已经到来）。
/// 分发入口dispatchTransformedTouchEvent：参数是非cancel，对象是child。（即分发事件到child）。
/// 我觉得这里能够进入调用，除非是ACTION_DOWN事件，即新的一次事件到来。没有测试，不敢保证。
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
/// dispatchTransformedTouchEvent其实就是调用了dispatchTouchEvent。这里是child::dispatchTouchEvent。
/// 如果返回true，表示child::dispatchTouchEvent返回true，意味着child view接收这次新的事件。
// 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();
/// ACTION_DOWN事件后，当前的child表明自己能够接收事件，所以加入到TouchTarget链表中。
/// 这样，下一个ACTION_MOVE/UP等事件就直接分发到child，而不再需要这里的dispatchTouchEvent。
/// 由于dispatchTouchEvent已经执行过，所以标识alreadyDispatchedToNewTouchTarget为true。
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();
}
/// 如果遍历了所有子View，发觉没有子View接收事件，那么将事件分发给最近响应了事件的View。
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;
}
}
}
/// 到这里可能有：
/// 1. 叶子
/// 2. 非叶子 且 非ACTION_DOWN的其它事件。
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
/// 如果是叶子，将这叶子作为普通View分发事件。
// No touch targets so treat this as an ordinary view.
//重点// 事件分发!!
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
/// 非叶子，遍历子View分发事件。
// 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;
//重点// 事件分发!! intercepted如果为true，则cancelChild就一直为true。
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;
}
}
有点长，没关系。
ViewGroup继承于View，重写了dispatchTouchEvent，将事件分发给ViewGroup自身或某一个子View。
收到ACTION_DOWN表示一次新的触摸事件，进行了状态的清理。
-
先执行onInterceptTouchEvent()。但onInterceptTouchEvent并不是无条件执行，当且仅当下面条件符合才会执行：
- 启用了截获（先决条件）
- 是ACTION_DOWN事件；或者是非ACTION_DOWN事件，但必须含有子对象（非叶子）。
这里的叶子是指：ViewGroup可能含有子View，但事件没法往下传递（主动拦截或子View不接收事件），此时称这个ViewGroup为叶子。
-
DOWN事件到来，如果ViewGroup没有截获事件，且含有子View：
- 先获取事件是否分发给有焦点子View，是则直接分发到有焦点的子View。
- 如果有焦点的子View没能处理事件，或者触点不在有焦点的子View内，那么分发到其它可能的子View。
- 没有焦点，遍历所有子View，找到能够接收事件，且触点在子View范围内的那个子View。
- 如果那个child view已经在TouchTarget链表里，那么退出查找，直接将事件分发到child view。
- 如果那个child view不在TouchTarget链表里，将事件分发到child view，调用child view::dispatchTouchEvent，看child view是否对事件感兴趣。
- 如果child view::dispatchTouchEvent返回true，则表示child view表明关心事件，那么将其加入到TouchTarget链表里。
- 如果child view::dispatchTouchEvent返回false，则表示虽然点是在child view里，但child view不关心事件，继续查找下一个child。
- 如果Down事件child view::dispatchTouchEvent返回false，将不会把child view加入TouchTarget链表中，将导致后续的POINTER_DOWN/MOVE/UP事件都不再分发给该child view，因为除了DOWN事件外，其它事件仅分发给TouchTarget链表。（这就是onTouchEvent返回false的效果）
- 含有child view，但都没有child view对事件感兴趣，则将事件分发到最近响应了事件的View。
dispatchTransformedTouchEvent封装了下一个dispatchTouchEvent。即要么dispatchTouchEvent给自己，要么dispatchTouchEvent给子View。
子View要表明自己对事件感兴趣，则需要在ACTION_DOWN时，dispatchTouchEvent返回true。即使其它ACTION情况下dispatchTouchEvent返回false也没关系，只要ACTION_DOWN时dispatchTouchEvent返回true，属于这一次事件的MOVE/UP等都会分发到该View（因为它已经加入了TouchTarget链表了）。
仅当ViewGroup是叶子时，ViewGroup才会dispatchTouchEvent给自己。换句话，只要子View表明了接收事件，子View所在的ViewGroup就不会把事件分发给自己！所以，如果子View表明了接收事件，那么子View所在的ViewGroup就不会产生onTouch和onTouchEvent！
子View的dispatchTouchEvent坐标系，以父View为坐标系。其中getX表示父坐标系，getRawX才是屏幕坐标系。
/**
* 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.
* 根据参数有不同的行为。关键的参数是 boolean cancel，View child。
* 如果cancel是true，表示分发取消事件，否则分发的是参数中的MotionEvent。
* 如果child是null，表示分发对象是ViewGroup自身。
* 如果child非null，表示分发对象是子child对象。
*
* 也即是说，这个方法用来分发MotionEvent到参数中的View child，如果View child为null，则分发到ViewGroup自身。
*/
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.
/// 如果是取消事件：分发取消事件完成后，直接返回。
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
/// 此次调用，分发对象是自身
handled = super.dispatchTouchEvent(event);
} else {
/// 此次调用，分发对象的是子child对象
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;
/// 计算此次事件对应的触点数量，即pointerCount和对应的数组。
// 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.
/// 如果发觉信息不合法，直接认为分发没有处理，返回false。
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.
// 如果触点数量和上一次一样，我们可以小心的重用，否则需要复制。
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
/// 此次调用，分发对象是自身
handled = super.dispatchTouchEvent(event);
} else {
/// 此次调用，分发对象是子child对象，坐标系是相对于ViewGroup自身，重新计算坐标。
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
/// 分发完成，恢复坐标系。（这就是小心重用）
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
/// 到达这里有点复杂，只有两种情况：
/// 1. newPointerIdBits != oldPointerIdBits 可以到达。
/// 2. newPointerIdBits == oldPointerIdBits 且 child != null 且 child.hasIdentityMatrix()为false 可以到达。
/// 3. 其它情况则已经返回了。
// Perform any necessary transformations and dispatch.
if (child == null) {
/// 此次调用，分发对象是自身
handled = super.dispatchTouchEvent(transformedEvent);
} else {
/// 此次调用，分发对象是子child对象，坐标系是相对于ViewGroup自身，重新计算坐标。
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;
}
这个方法是dispatchTouchEvent的统一入口，如果参数View child不为null，则分发到View child，否则分发到ViewGroup自身。
参数中的int desiredPointerIdBits和触摸事件MotionEvent的封装有关，只是从MotionEvent里拿数据。
返回值就是dispatchTouchEvent的返回值，false表示未消化，true表示消化。
View child并不是仅仅只是View对象，它的指向可以是任何继承于View的对象。
仅当ViewGroup是叶子时，才调用View::dispatchTouchEvent。仅当事件是分发给自身时，才需要调用View::dispatchTouchEvent。换句话，事件分发最后，只要到了叶子，都会调用到View::dispatchTouchEvent。
事件的分发，一个MotionEvent对象跨越了一系列调用链，调用过程不能随意修改MotionEvent的数据，所以修改了要进行还原；或者修改前复制一个副本，在副本上修改。
View源码
/frameworks/base/core/java/android/view/View.java
/**
* 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.
*
* 表示事件已经分发到目标了。
*/
public boolean dispatchTouchEvent(MotionEvent event) {
/// 获取了焦点。
// 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);
}
/// ACTION_DOWN表示新的一次事件到来，清除状态
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
/// 如果是enabled，且注册了onTouchListener，则调用当前View的onTouch!! enabled的真假，并不影响onTouchEvent的调用！
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
/// 紧接着，如果onTouch返回的是false，表示onTouch未消化事件，则调用当前View的onTouchEvent！！！
/// 注意，如果enabled为false，也会执行onTouchEvent。
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;
}
从没觉得如此简单：
-
无论是ViewGroup还是View，onTouch和onTouchEvent都是在dispatchTouchEvent中触发。调用顺序为：dispatchTouchEvent - onTouch - onTouchEvent。
- 对于View，由于是叶子，毫无疑问，就是：View::dispatchTouchEvent - View::onTouch - View::onTouchEvent。
- 对于ViewGroup，如果是叶子，也是：ViewGroup::dispatchTouchEvent - ViewGroup::onTouch - ViewGroup::onTouchEvent。
- 对于ViewGroup，如果不是叶子，是：ViewGroup::dispatchTouchEvent - ChildView::dispatchTouchEvent(onTouch - onTouchEvent都在此触发) - ViewGroup::onTouch - ViewGroup::onTouchEvent。
事件分发就是这么一回事，都在一个dispatchTouchEvent方法内就分发完成。
Enabled下，当目标Target自身的onTouch返回false，自身的onTouchEvent才能被执行。而Disabled下，onTouch不会调用，但onTouchEvent能调用！！
dispatchTouchEvent返回false，仅当onTouch返回false且onTouchEvent返回false。表示目标不关心事件。
dispatchTouchEvent返回true，可以是onTouch返回true，或者onTouch返回false，但onTouchEvent返回true。表示目标关心事件。
要表明当前View对事件感兴趣，则需要在ACTION_DOWN时，dispatchTouchEvent返回true。
大致的调用链（核心）：
// 事件分发入口
dispatchTouchEvent() {
onIntercept
dispatchTouchEvent() {
onIntercept
dispatchTouchEvent() {
onIntercept
...
dispatchTouchEvent() {（叶子）
if (! onTouch()) {
onTouchEvent()
}
}
...
onTouch
onTouchEvent
}
onTouch
onTouchEvent
}
onTouch
onTouchEvent
}
对于事件分发的入口，只需要一个。所以如果你要自定义一个事件分发器，仅需一个方法接口就足够了。
调用链自上而下，只要其中一个方法返回true，则表示事件被消化，分发完成！！所以，越在调用链下面，调用的条件越苛刻。
对于Target自身，onTouch和onTouchEvent并没有什么区别，仅仅是调用先后顺序不同而已。（这也解释了，GestureDetector既可以放在目标的onTouch，也可以放在目标的onTouchEvent）
父View有拦截的权利，子View有优先响应事件的权利。
onIntercept可以提供截获的机会，返回true表示停止调用链的下潜，将自身作为叶子看待。
原生不支持调用链从头到尾都能执行。虽然所有onIntercept返回false，所有dispatchTouchEvent返回false，所有onTouch返回false，所有onTouchEvent返回false时，ACTION_DOWN事件可以在调用链执行一遍，但也仅仅限于ACTION_DOWN事件。要真正实现一个完整的事件可以被调用链所有View消化，必须重写掉TouchTarget链表。
附录：
继承关系图
实例讲解。
一般的视图
图中，有以下实例：
- Activity实例
- ListView实例 - ViewGroup - View
- TextView实例 - View
涉及继承，就有覆盖重写，override会导致调用顺序发生改变！最重要看清实例！实例！实例！
事件分发模型：
// 事件分发入口
Activity::dispatchTouchEvent(MotionEvent ev)
|
PhoneWindow::superDispatchTouchEvent(MotionEvent ev)
|
DecorView::superDispatchTouchEvent(MotionEvent event)
|
FrameLayout::dispatchTouchEvent(MotionEvent event)
|
ViewGroup::dispatchTouchEvent(MotionEvent ev)
DecorView::onInterceptTouchEvent(MotionEvent ev)
FrameLayout::onInterceptTouchEvent(MotionEvent ev)
ViewGroup::onInterceptTouchEvent(MotionEvent ev)
|
ListView::dispatchTouchEvent(MotionEvent ev)
|
ViewGroup::dispatchTouchEvent(MotionEvent ev)
ListView::onInterceptTouchEvent(MotionEvent ev)
ViewGroup::onInterceptTouchEvent(MotionEvent ev)
|
TextView::dispatchTouchEvent(MotionEvent ev)
|
View::dispatchTouchEvent(MotionEvent ev)
TextView::onTouch(MotionEvent ev)
View::onTouch(MotionEvent ev)
TextView::onTouchEvent(MotionEvent ev)
View::onTouchEvent(MotionEvent ev)
|
ListView::onTouch(MotionEvent ev)
ViewGroup::onTouch(MotionEvent ev)
View::onTouch(MotionEvent ev)
ListView::onTouchEvent(MotionEvent ev)
ViewGroup::onTouchEvent(MotionEvent ev)
View::onTouchEvent(MotionEvent ev)
....
....
ListView只是举例，可以使用RelativeLayout代替。
功能1: 点击TextView能够响应。
要事件传递到TextView，则说明从上而下，调用链要直达TextView。所以TextView之前的onIntercept要返回false，这样dispatch才能分发到TextView。
TextView的dispatchTouchEvent要返回true，表明TextView关心事件！
dispatchTouchEvent要返回true，要么TextView的onTouch返回true，要么TextView的onTouchEvent返回true。要么TextView重写dispatchTouchEvent返回true。
功能2: 禁用TextView的响应。
要禁用TextView的响应，只需要从调用链到TextView之前进行截获即可。所以，ListView重写onInterceptTouchEvent返回true，将ListView作为叶子，事件就不会再往下分发（包括ACTION_DOWN事件）。
TextView中重写View的dispatchTouchEvent返回false，表明TextView不关心事件（但仍旧会收到ACTION_DOWN事件）。如果重写过程如果不调用super，将导致onTouch和onTouchEvent都不会调用到。
TextView中重写View的onTouch返回false，重写View的onTouchEvent返回false（但也仍旧能收到ACTION_DOWN事件）。
一旦TextView在第一次dispatchTouchEvent中返回false，后续将不再收到MOVE/UP等事件，直到下一次ACTION_DOWN到来（见上面的TouchTarget链表)。
由于调用链中都返回false，所以ACTION_DOWN事件在调用链中执行了一遍，但也仅仅只有ACTION_DOWN事件。后续的事件被截获！
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyTextView: onTouch() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyTextView: onTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyViewGroup: onTouch() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MyViewGroup: onTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=17.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366519, downTime=745366519, deviceId=7, source=0x1002 }]
// ACTION_DOWN在调用链中执行了一次，后续的事件就被顶层截获消化
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366534, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366534, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=745366551, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=745366551, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=745366568, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=745366568, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366584, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366584, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366618, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=745366618, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366618, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366618, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366629, downTime=745366519, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=121.887146, y[0]=263.86258, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=745366629, downTime=745366519, deviceId=7, source=0x1002 }]
功能3：重写TextView的dispatchTouchEvent为
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.d(TAG, "dispatchTouchEvent() called with: event = [" + event + "]");
if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
return true;
}
return super.dispatchTouchEvent(event);
}
输出：
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506673, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506673, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506673, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506673, downTime=750506673, deviceId=7, source=0x1002 }]
// MyTextView在action=ACTION_DOWN时直接返回true，导致onTouch和onTouchEvent没能执行。
// 由于表明了关心事件，下面的ACTION_MOVE继续分发到TextView，此时由于调用的是super，所以会执行到onTouch和onTouchEvent。
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouch() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750506690, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouch() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750506723, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouch() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506737, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouch() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MyTextView: onTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=24.858917, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=131.8779, y[0]=270.85892, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750506740, downTime=750506673, deviceId=7, source=0x1002 }]
改为：
```java
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.d(TAG, "dispatchTouchEvent() called with: event = [" + event + "]");
if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
return true;
}
return false;
}
输出：
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911608, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911608, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911608, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911608, downTime=750911608, deviceId=7, source=0x1002 }]
// 在DOWN事件中，TextView::dispatchTouchEvent直接返回true，导致onTouch和onTouchEvent都没有调用。
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750911624, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750911624, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750911624, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750911624, downTime=750911608, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=750911624, downTime=750911608, deviceId=7, source=0x1002 }]
// 在其它事件中，TextView::dispatchTouchEvent直接返回false，导致onTouch和onTouchEvent都没有调用，直接将事件抛到上层。
// 由于TextView声明为关心事件，所以ViewGroup不会分发到自身，自然就没有onTouch和onTouchEvent。
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750911641, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750911641, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750911641, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750911641, downTime=750911608, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=750911641, downTime=750911608, deviceId=7, source=0x1002 }]
D/MainActivity: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911721, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: dispatchTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911721, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyViewGroup: onInterceptTouchEvent() called with: ev = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911721, downTime=750911608, deviceId=7, source=0x1002 }]
D/MyTextView: dispatchTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=38.851624, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911721, downTime=750911608, deviceId=7, source=0x1002 }]
D/MainActivity: onTouchEvent() called with: event = [MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=118.889915, y[0]=284.85162, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=750911721, downTime=750911608, deviceId=7, source=0x1002 }]
图解：
如图，
事件分发，从窗口到Activity到ViewGroup再到View，经历着ABCD四个节点。
事件分发从父到子，向下分发（父的dispatch先于子的dispatch）。
事件响应从子到父，向上冒泡，子不响应父才有机会响应（子的onTouch先于父的onTouch）。
DOWN事件，最深分发到最先返回true的那个View。
其它事件，最深分发到上面DOWN事件记录的那个View，按DOWN事件记录的路径分发。
只有DOWN事件关心触点范围的View，其它事件按DOWN事件记录的路径依次分发到最深的那个View
一次完整的事件分发流图
DOWN - Activity - ...- ViewGroupZ - ViewA - onTouch - true - END
MOVE - Activity - ...- ViewGroupZ - ViewA - onTouch - ? - END
UP - Activity - ...- ViewGroupZ - ViewA - onTouch - ? - END
意思是：
DOWN事件，最先返回true的是ViewA。
后续的MOVE／UP事件，最深分发到ViewA，此时无论MOVE／UP是否在ViewA之上，都按照DOWN事件记录的到ViewA的路径分发。ViewA返回true分发结束；返回false事件冒泡，但没有意义，因为DOWN事件仅被ViewA消化了。虽然最深可以到ViewA，但分发过程可以截获。
总结，DOWN事件返回true的那个View决定了事件向下分发的深度，决定了其它事件向下分发的路径，决定了事件最终响应的View。
以上是不改动Android的事件分发机制情况下，正常的分发流程。可以通过修改其中某个节点，改变事件的分发和响应：
- 修改时机A：父可以在onIntercept截获事件，优先处理。如果父在DOWN事件时没有截获，但在其它事件将其截获，将导致子收到ACTION_CANCEL。当且仅当在onIntercept截获才有事件。在dispatch时截获不会有事件。ACTION_CANCEL向下分发最深到DOWN记录的View，向上冒泡不超过进行截获的View。
- 修改时机B：子可以在onTouch处理事件。
- 修改时机C：子可以在onTouchEvent处理事件（效果同B）。
- 修改时机D：父可以重写dispatch分发函数，将事件一一分发到子View而不管子View的返回值，实现事件透传，多级响应。
总结：
dispatchTouchEvent在ACTION_DOWN返回true，表示关心事件；此时包含此View的ViewGroup将不会有onTouch和onTouchEvent发生（相当于子View吃掉了）。
dispatchTouchEvent在ACTION_DOWN返回false，表示不关心事件；后续的ACTION_DOWN/UP等事件都不会再分发到当前View，而是被父截获（相当于子View不吃就没机会再吃）。
dispatchTouchEvent的返回值，可以通过dispatchTouchEvent／onTouch／onTouchEvent控制。onTouch和onTouchEvent由
super.dispatchTouchEvent调用，并返回其返回值。onTouch前提是开启了Enabled。
onTouchEvent前提是Disabled。或者Enabled状态下，onTouch返回false（测试过）。
ACTION_DOWN是一次手势事件／触摸事件的开始。
ViewGroup才有onInterceptTouchEvent。
onInterceptTouchEvent前提是没有禁用截获。
ACTION_DOWN在目标外，然后划过目标释放，目标不会收到任何事件。ACTION_DOWN在目标内，然后划出目标释放，目标会收到父发送过来的ACTION_MOVE/UP等事件。
事件都是先从父dispatcher然后到子dispatcher，如果不拦截，先到子的onTouch／onTouchEvent，后到父的onTouch／onTouchEvent。所以，在子View上点击，子View是有优先响应权的。