Android 事件分发机制(最新源码6.0分析)--ViewGrop
ViewGroup的事件分发机制
转载请标明出处：http://blog.csdn.net/u014800493/article/details/52056311
上一张说到View的事件处理机制。而在Activity的dispatchTouchEvent()中最终定位到了ViewGroup（）的事件分发：
上一章 请看：这里Android 事件分发机制--View
还是先看下ViewGroup的层级结构图吧：
上章也说过了，我们用到的布局Layout全部继承ViewGroup 如：FrameLayout,RelativeLayout,LineraLayout等等。
首先还是看看XML：
而LinearLayout高度设置为200，背景白色，最外层设置为黑色。看看MyLinearLayout:
/**
* @author Gordon
* @since 2016/7/27
* do()
*/
public class MyLinearLayout extends LinearLayout {
public MyLinearLayout(Context context) {
super(context);
}
public MyLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public MyLinearLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.i("layout","Layout_dispatchTouchEvent");
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.i("layout","Layout_onInterceptTouchEvent");
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("layout","Layout_onTouchEvent");
return super.onTouchEvent(event);
}
}
看看MyButton：其实上一章已经说过了
/**
* @author Gordon
* @since 2016/7/27
* do()
*/
public class MyButton extends Button {
public MyButton(Context context) {
super(context);
}
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public MyButton(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("button","Button_onTouchEvent");
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.i("button","Button_dispatchTouchEvent");
return super.dispatchTouchEvent(event);
}
}/**
* @author Gordon
* @since 2016/8/1
* do()
*/
public class MyTextView extends TextView {
public MyTextView(Context context) {
super(context);
}
public MyTextView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyTextView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public MyTextView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("textview","TextView_onTouchEvent");
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.i("textview","TextView_dispatchTouchEvent");
return super.dispatchTouchEvent(event);
}
}/**
* @author Gordon
* @since 2016/8/1
* do()
*/
public class MyImageView extends ImageView {
public MyImageView(Context context) {
super(context);
}
public MyImageView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public MyImageView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("imageview","ImageView_onTouchEvent");
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.i("imageview","ImageView_dispatchTouchEvent");
return super.dispatchTouchEvent(event);
}
}
其实比较一下，这里layout比子view多了个onInterceptTouchEvent（）方法。这些方法到底怎么运作的
看下Activity的代码：public class OnClickEventActivity extends Activity {
@Bind(R.id.button_onclick)
MyButton click_button;
@Bind(R.id.text_onclick)
MyTextView click_text;
@Bind(R.id.image_onclick)
MyImageView click_image;
@Bind(R.id.layout_button_onclick)
ViewGroup click_layout;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_onclick_layout);
ButterKnife.bind(this);
clickAble();
initView();
}
private void clickAble() {
Log.i("button", "Button_isClick="+click_button.isClickable());
Log.i("textview", "TextView_isClick="+click_text.isClickable());
Log.i("imageview", "ImageView_isClick="+click_image.isClickable());
}
private void initView() {
click_button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.i("button", "Button_OnClick");
}
});
click_button.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
Log.i("button", "Button_setOnTouchListener");
return false;
}
});
click_text.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.i("textview", "textview_OnClick");
}
});
click_text.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
Log.i("textview", "textview_setOnTouchListener");
return false;
}
});
click_image.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.i("imageview", "imageview_OnClick");
}
});
click_image.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
Log.i("imageview", "imageview_setOnTouchListener");
return false;
}
});
click_layout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.i("layout", "Layout_OnClick");
}
});
click_layout.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.i("layout", "Layout_OnTouchListener");
return false;
}
});
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("activity", "Activity_onTouchEvent");
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.i("activity", "Activity_dispatchTouchEvent");
return super.dispatchTouchEvent(ev);
}
}
initView()方法主要是设置Button，TextView，ImageView以及他们的parent的layout的事件，也就是添加Listener。
先来看看运行的结果图：
看下log：
可以看出Button的默认clickable为true。而TextView和ImageView 默认为false。
先说明一下，一次点击事件，包括Event的Action_down和Action_up所以TouchEvent事件会执行2次。
先点击一下黑色区域。看下log：
没什么说的，走向为：Activity_dispatchTouchEvent-------- >Activity_ouTouchEvent
再来点击一下上面的白色空白区域。看下log:
到这里的走向：Activity_dispatchTouchEvent------>Layout_dispatchTouchEvent------>Layout_onTouchListener(onTouch())
---->Layout_onTouchEvent---->Layout_onClick.
其实你会发现到这为止的log 和上一章说的没啥区别。这里的内层LinearLayout也即是白色的区域，相当于上一章的button。
至于为什么没有走activity_ouTouchEvent 也说过了。是因为被Layout的点击事件拦截并且处理掉了，至于怎么拦截怎么处理。
先别急，继续点击button，看下log：
先来看下方法的走向：Activity_dispatchTouchEvent------>Layout_dispatchTouchEvent------>Layout_onInterceptTouchEvent
---->Button_dispatchTouchEvent------>Button_setOnTouchEvent(onTouch())------>Button_onTouchEvent------->Button_onClick
仔细看一下发现（Layout_onTouchEvent---->Layout_onClick）都没有执行。而且多了个（Layout_onInterceptTouchEvent）
这又是为什么呢，会是我们所说的被拦截掉了吗，而（Layout_onInterceptTouchEvent）又是干什么的呢？
这一系列的问题，让我们看下源码便知，先来看看Layout_diapatchonTouchEvent方法的源码：
/**
* {@inheritDoc}
*/
@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.
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;
}
// 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.
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;
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.
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.
final ArrayList preorderedList = buildOrderedChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : i;
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.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
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;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// 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;
}
}
// 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;
} 继续往下看 12行的if语句处理一些焦点问题。继续往下，17行的onFilterTouchEventForSecurity()方法是什么呢？看下
源码：
/**
* Filter the touch event to apply security policies.
*
* @param event The motion event to be filtered.
* @return True if the event should be dispatched, false if the event should be dropped.
*
* @see #getFilterTouchesWhenObscured
*/
public boolean onFilterTouchEventForSecurity(MotionEvent event) {
//noinspection RedundantIfStatement
if ((mViewFlags & FILTER_TOUCHES_WHEN_OBSCURED) != 0
&& (event.getFlags() & MotionEvent.FLAG_WINDOW_IS_OBSCURED) != 0) {
// Window is obscured, drop this touch.
return false;
}
return true;
}
- // 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();
- }
/**
* Resets all touch state in preparation for a new cycle.
*/
private void resetTouchState() {
clearTouchTargets();
resetCancelNextUpFlag(this);
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
mNestedScrollAxes = SCROLL_AXIS_NONE;
}
第3句重置了disalloIntercept. ViewGroup中disalloIntercept默认为false。注意一下，这里可能和后面的requestDisallowIntercept()
方法设置无效有关。继续往下：
- // 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;
- }
是什么呢？这里是判断是否设置了disallowIntercept，也就是是否设置了拦击。这里可以通过如下方法进行设置：
/**
* {@inheritDoc}
*/
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);
}
}当然前面说了，disalloIntercept默认是false。然后继续往下进入if语句中。重点来了：
onInterceptTouchEvent(ev)方法出现了，点进去看看里面是什么代码：
/**
* Implement this method to intercept all touch screen motion events. This
* allows you to watch events as they are dispatched to your children, and
* take ownership of the current gesture at any point.
*
* Using this function takes some care, as it has a fairly complicated
* interaction with {@link View#onTouchEvent(MotionEvent)
* View.onTouchEvent(MotionEvent)}, and using it requires implementing
* that method as well as this one in the correct way. Events will be
* received in the following order:
*
*
* - You will receive the down event here.
*
- The down event will be handled either by a child of this view
* group, or given to your own onTouchEvent() method to handle; this means
* you should implement onTouchEvent() to return true, so you will
* continue to see the rest of the gesture (instead of looking for
* a parent view to handle it). Also, by returning true from
* onTouchEvent(), you will not receive any following
* events in onInterceptTouchEvent() and all touch processing must
* happen in onTouchEvent() like normal.
*
- For as long as you return false from this function, each following
* event (up to and including the final up) will be delivered first here
* and then to the target's onTouchEvent().
*
- If you return true from here, you will not receive any
* following events: the target view will receive the same event but
* with the action {@link MotionEvent#ACTION_CANCEL}, and all further
* events will be delivered to your onTouchEvent() method and no longer
* appear here.
*
*
* @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) {
return false;
}代码很简单，直接返回的false。但是注释很长。就不一一解释了。直接看注释的@return那里。
如果此方法直接返回了true。就会拦截子View 的所有事件。是不是这样的呢，我们试试就知道了。
把Avtivity代码中的MyLinearLayout的onInterceptTouchEvent方法直接返回true。看下log：
无论点击Button，TextView，ImageView都是这个log。也验证了上面的说法。继续往下
49-58行主要是检测Event是否cancle事件等等。不多说。继续：
61行语句。如果没有cancel并且没有intercept事件。进入if语句内。
71行的if语句不多说也就是判断是不是Action_down,move等，
80行的removePointersFromTouchTargets()清除之前的Touch目标。接下来重点来了
- 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 = buildOrderedChildList(); - final boolean customOrder = preorderedList == null
- && isChildrenDrawingOrderEnabled();
- final View[] children = mChildren;
- for (int i = childrenCount - 1; i >= 0; i--) {
- final int childIndex = customOrder
- ? getChildDrawingOrder(childrenCount, i) : i;
- 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.
- if (childWithAccessibilityFocus != null) {
- if (childWithAccessibilityFocus != child) {
- continue;
- }
- childWithAccessibilityFocus = null;
- i = childrenCount - 1;
- }
- if (!canViewReceivePointerEvents(child)
- || !isTransformedTouchPointInView(x, y, child, null)) {
- ev.setTargetAccessibilityFocus(false);
- continue;
- }
- newTouchTarget = getTouchTarget(child);
- if (newTouchTarget != null) {
- // Child is already receiving touch within its bounds.
- // Give it the new pointer in addition to the ones it is handling.
- newTouchTarget.pointerIdBits |= idBitsToAssign;
- break;
- }
- resetCancelNextUpFlag(child);
- 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;
- }
- // 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();
- }
接收point事件。
28行 先看下canViewReceivePointerEvents（）和isTransformedTouchPointInView()方法：
/**
* Returns true if a child view can receive pointer events.
* @hide
*/
private static boolean canViewReceivePointerEvents(View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
} /**
* Returns true if a child view contains the specified point when transformed
* into its coordinate space.
* Child must not be null.
* @hide
*/
protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
final float[] point = getTempPoint();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}其实这两个判断就是判断当前childView是否真正的接收到此Event。如果都没有，continue，结束本次循环。
如果有继续往下。
35行，如果child准备处理此次Event。结束for循环，继续往下。如果没有，继续执行for循环。
43行 dispatchTransformedTouchEvent()方法。多次在dispatchTouchEvent（）方法中调用到。
如最上面的ViewGroup的dispatchTouchEvent()源码中的168和182行。都调用了此方法。
进去看看到底是啥：
/**
* 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;
}如果不为空，根据条件调用child.dispatchEvent().如果chid或者child的parent有消耗此事件的返回true。没有则返回false。
到这了大概明白了。无论在上面的for循环内外。如果layout的所有childView中有接收并处理了Event事件，会直接消耗此Event。
如果没有则返回上一级layout处理此次Event，知道消耗此Event为止。如下图：
上图描述了VieGroup 的事件分发事件。也就是说如果没有消耗事件（返回false）。就会交给parent去处理。以此类推。
打个比方：一个团队老板要发个任务。流程为：
BOSS-------->研发经理--------->架构师---------->小组组长----------->个人
如果个人处理了此事件（返回true）。会反馈给上级，以此类推谁处理好了。
个人 --------> 小组组长--------> 架构师 --------> 研发经理-------->BOSS
如果个人没有处理好（返回false），组长就是处理此事情，如果继续返回false，继续交给上级处理，以此类推。
（view，viewGroup的onclick()事件，也就是点击事件是在onTouchEvent()的Action_up中执行的，这里就没加进去）
下面看下案例：
比如最上面的Activity如果把initView()方法注释掉，也就是不给childView添加任何的事件listener。看下log：
此为button的点击log图，看下textView的点击log：
此为TexiView的log图。看下ImageView的log图
有人会发现在没设置listener的时候，button执行完自己的onTouchEvent()后并没有返回给parent处理。而是直接消耗了
而TextView和ImageView没有消耗事件而是返回给parent去处理了。
让我们来看看最开头的log出的Button，TextView，ImagView的默认clickable.
Button为true。TextView，ImageView为false。为什么true就会消耗此事件呢？
上一章我们已经说过原因了。可以看下 Android 事件分发机制--childView
简单说下就是：在View 的onTouchEvent()方法中，如果view 的Clickable，或者longClickable或者contextClickable
任何一个为true。无论View是不是Enable的，都会返回true（消耗此事件）。具体原因看下上一章。
总结：
到此View,ViewGroup的事件分发机制已经说完了。花了很多精力，主要的还是要自己去实践
实践中结合源码去看，就会记忆深刻啦。