Android(安卓)事件分发机制(最新源码6.0分析)--ViewGrop
16lz
2021-01-26
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：
<?xml version="1.0" encoding="utf-8"?> 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。
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