事件分发机制并不是洪水猛兽
文章目录
- OnTouchListener与OnClickListener的优先级
- 事件分发
- 滑动冲突
- 处理滑动冲突
- 1. 内部拦截法
- 2.外部拦截法
当MotionEvent产生后，系统总归要将其传递到某个View，这个过程就是事件分发。事件分发机制离不开3个重要方法：dispatchTouchEvent（分发）、onInterceptTouchEvent（拦截，在dispatchTouchEvent中调用。需要注意，View中没有该方法）、onInterceptTouchEvent（处理事件，在dispatchTouchEvent中调用。）
这3个方法相爱相杀，紧密关联。ViewGroup收到点击事件后，它的dispatchTouchEvent方法首先会被调用。如果它的onInterceptTouchEvent方法返回了true，表示ViewGroup要将“快递”拦截下来，事件就成了“拦截件”。随后它的onTouchEvent会被调用来处理这件“快递”。如果ViewGroup的onInterceptTouchEvent返回了false，那么ViewGroup就不会拦截。快递就送到了View手里，View的dispatchTouchEvent就会被调用。如此循环往复，直到事件被处理。
OnTouchListener与OnClickListener的优先级
提到事件处理，当对一个Button同时设置了setOnTouchListener和setOnClickListener后，如果OnTouchListener的onTouch方法return 了false，那么两个方法都会执行。如果return了true，则只有onTouch被执行，onClick不会被执行。
现在通过源码分析原因：
View.java#dispatchTouchEvent()
...
if (onFilterTouchEventForSecurity(event)) {if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {result = true;}//mListenerInfo是单例处理返回的对象ListenerInfo li = mListenerInfo;if (li != null && li.mOnTouchListener != null&& (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnTouchListener.onTouch(this, event)) {result = true;}if (!result && onTouchEvent(event)) {result = true;}
}
...
这个mListenerInfo就是单例处理返回的一个ListenerInfo 对象，这就保证了mListenerInfo 肯定不为null，即li != null：
ListenerInfo getListenerInfo() {if (mListenerInfo != null) {return mListenerInfo;}mListenerInfo = new ListenerInfo();return mListenerInfo;
}
它里面有着众多xxxListener，如：
public OnClickListener mOnClickListener;protected OnLongClickListener mOnLongClickListener;private OnTouchListener mOnTouchListener;
而我们setOnTouchListener时，就会将new出来的OnTouchListener 赋值过来，这就保证了li.mOnTouchListener != null。
我们setOnTouchListener重写的onTouch方法的返回值起到了决定性的作用，它影响了if条件语句的执行。如果return true，那就所有的条件都满足，万事大吉，程序走进if里，result = true。如果重写的onTouch方法return了false，那么整个if条件语句就不满足，就不再会往里走了。
在仔细看if块：
if (!result && onTouchEvent(event)) {result = true;}
如果result为true的话，那么“&&”前面就是false，onTouchEvent(event)就没有再执行的必要了。onTouchEvent负责事件的消费，而onClick是在MotionEvent.ACTION_UP中被调用—>performClickInternal()—>performClick():
public boolean performClick() {// We still need to call this method to handle the cases where performClick() was called// externally, instead of through performClickInternal()notifyAutofillManagerOnClick();final boolean result;final ListenerInfo li = mListenerInfo;if (li != null && li.mOnClickListener != null) {playSoundEffect(SoundEffectConstants.CLICK);//这才是亮点！！！li.mOnClickListener.onClick(this);result = true;} else {result = false;}sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);notifyEnterOrExitForAutoFillIfNeeded(true);return result;
}
这个if判断和刚才onTouch时的if是十分类似的。前面已经分析过了，if里面的条件都满足，于是就往里走，调用了 li.mOnClickListener.onClick(this)。至此，我们setOnClickListener就会响应点击事件了。
总结一下，TouchEvent发射出来一个信号，如果被onTouch拦截到了，自然就没onClick什么事了。可如果一旦onTouch没拦截到这个信号，onClick就会成功处理这个信号。
事件分发
事件产生后的传递顺序如下：
来看ViewGroup对事件的分发过程，dispatchTouchEvent方法：
if (actionMasked == MotionEvent.ACTION_DOWN) {// 判断为DOWN事件，清除掉一些变量，重置状态cancelAndClearTouchTargets(ev);resetTouchState();
}// 没有拦截，为false
final boolean intercepted;
//当事件被ViewGroup的子元素成功处理时，mFirstTouchTarget会被赋值并指向子元素
//换句话说，当ViewGroup不拦截，并将事件交给子元素处理时，mFirstTouchTarget != null成立
if (actionMasked == MotionEvent.ACTION_DOWN|| mFirstTouchTarget != null) {final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;if (!disallowIntercept) {intercepted = onInterceptTouchEvent(ev);ev.setAction(action); // restore action in case it was changed} else {intercepted = false;}
} else {// There are no touch targets and this action is not an initial down// so this view group continues to intercept touches.intercepted = true;
}
首先判断为ACTION_DOWN事件，会清除掉一些变量、重置状态。
后续有一个变量：final boolean intercepted。如果没有拦截，intercepted为false。这里有一个特殊情况：标志位FLAG_DISALLOW_INTERCEPT。这个标志位是在requestDisallowInterceptTouchEvent方法内设置的，一旦它被设置，那么ViewGroup就无法拦截除DOWN事件以外的其他事件（MOVE/UP等事件）。当ViewGroup分发事件时，DOWN事件会重置该标志位，导致子View的“努力徒劳”。当ViewGroup面临DOWM事件时，总会调用自己的onInterceptTouchEvent方法询问是否需要拦截事件。resetTouchState方法会对该标志位进行重置，故子View调用requestDisallowInterceptTouchEvent方法并不能影响ViewGroup对DOWM事件的处理结果，这一点，在使用内部拦截法处理滑动冲突时会得到验证。
然后往下走，
if (newTouchTarget == null && childrenCount != 0)
newTouchTarget 肯定为null，因为上面没几行刚刚赋值为null。childrenCount 表示控件的个数，肯定不为0，所以就会继续往里走下去，会遇到
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
buildTouchDispatchChildList()—>return buildOrderedChildList():对子view进行排序。
ArrayList<View> buildOrderedChildList() {final int childrenCount = mChildrenCount;if (childrenCount <= 1 || !hasChildWithZ()) return null;if (mPreSortedChildren == null) {//专门用来存放排序后的child的mPreSortedChildren = new ArrayList<>(childrenCount);} else {// callers should clear, so clear shouldn't be necessary, but for safety...mPreSortedChildren.clear();mPreSortedChildren.ensureCapacity(childrenCount);}final boolean customOrder = isChildrenDrawingOrderEnabled();for (int i = 0; i < childrenCount; i++) {// add next child (in child order) to end of listfinal int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);final View nextChild = mChildren[childIndex];//获取View在Z轴方向的值final float currentZ = nextChild.getZ();// insert ahead of any Views with greater Zint insertIndex = i;//mPreSortedChildren 就是上面刚刚new出来的数组。专门用来存放排序后的children//从数组取出来和当前的currentZ比较，while里就是将Z值较大的往后放，较小的往前排。while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {insertIndex--;}mPreSortedChildren.add(insertIndex, nextChild);}return mPreSortedChildren;
}for循环中通过nextChild.getZ()来获取到currentZ，currentZ就是View在Z轴方向上的值（码积木一样，View都是一层层码上去的）。
越靠上的View，它的currentZ就越大。mPreSortedChildren 用来存放排序后的children。while里将Z值大的View放后，Z值小的往前排。
最后将排序好的数组返回。
preorderedList 就是return的排好序的数组，随后还会经历一个for循环。对排好序的数组的循环从childrenCount -1开始，也就是先从数组最后开始。通过getAndVerifyPreorderedIndex方法获取对应的childIndex，并进一步获取到响应的child（就是我们的Button等控件View）。
//从数组最后面，currentZ最大的开始for (int i = childrenCount - 1; i >= 0; i--) {//先拿到View的下标final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);//根据下标，得到View（如：Button） final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex);if (childWithAccessibilityFocus != null) {if (childWithAccessibilityFocus != child) {continue;}childWithAccessibilityFocus = null;i = childrenCount - 1;}//拿到Button后，canViewReceivePointerEvents判断点击是否是动画、是否可见，//isTransformedTouchPointInView判断点击是否在View上。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);//dispatchTransformedTouchEvent负责将事件分发给谁来处理事件，return handled = child.dispatchTouchEvent(transformedEvent);//这意味这事件已经传递到View中了。//View#dispatchTouchEvent的返回结果--->result 只有当onTouchEvent处理后，result才为true。//换句话说，当Button处理了事件，才会命中这个if，break掉for循环；如果Button没处理，就开始下一次循环，取出比Button的currentZ值更小的父容器，将事件交给它。//Button处理事件就处理，Button不处理，就往上传递交给Button的父容器。如果父容器也不处理，那就交给父容器的父容器......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 indexfor (int j = 0; j < childrenCount; j++) {if (children[childIndex] == mChildren[j]) {mLastTouchDownIndex = j;break;}}} else {mLastTouchDownIndex = childIndex;}mLastTouchDownX = ev.getX();mLastTouchDownY = ev.getY();//Button处理事件后，调用addTouchTarget方法--->mFirstTouchTarget!=null--->newTouchTarget==mFirstTouchTargetnewTouchTarget = 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);}
将事件从ViewGroup分发给View，这样事件的处理就走到了View上，于是事件就得到了它应有的处理（这个方法不止一次被调用，而且有很大区别，第三个参数是否为null）：
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {......//child不为null，就执行else中的child.dispatchTouchEvent(transformedEvent)方法//也就是调用Button的dispatchTouchEvent方法。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());}//这调用的就是Button的dispatchTouchEvent方法，即事件已经传递到View中了handled = child.dispatchTouchEvent(transformedEvent);}// Done.transformedEvent.recycle();return handled;
}
返回的handled，即handled = child.dispatchTouchEvent(transformedEvent)也就是返回View#dispatchTouchEvent的返回结果--->result
public boolean dispatchTouchEvent(MotionEvent event) {// If the event should be handled by accessibility focus first.if (event.isTargetAccessibilityFocus()) {// We don't have focus or no virtual descendant has it, do not handle the event.if (!isAccessibilityFocusedViewOrHost()) {return false;}// We have focus and got the event, then use normal event dispatch.event.setTargetAccessibilityFocus(false);}boolean result = false;if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onTouchEvent(event, 0);}final int actionMasked = event.getActionMasked();if (actionMasked == MotionEvent.ACTION_DOWN) {// Defensive cleanup for new gesturestopNestedScroll();}if (onFilterTouchEventForSecurity(event)) {if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {result = true;}//noinspection SimplifiableIfStatementListenerInfo li = mListenerInfo;if (li != null && li.mOnTouchListener != null&& (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnTouchListener.onTouch(this, event)) {result = true;}//当onTouchEvent处理后，result才为true。if (!result && onTouchEvent(event)) {result = true;}}if (!result && mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);}// Clean up after nested scrolls if this is the end of a gesture;// also cancel it if we tried an ACTION_DOWN but we didn't want the rest// of the gesture.if (actionMasked == MotionEvent.ACTION_UP ||actionMasked == MotionEvent.ACTION_CANCEL ||(actionMasked == MotionEvent.ACTION_DOWN && !result)) {stopNestedScroll();}return result;
}
再回到ViewGroup#dispatchTouchEvent中的if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign))中。如果事件被Button处理完，会返回handled （= child.dispatchTouchEvent(transformedEvent)），View#dispatchTouchEvent方法的返回值和View自己的onTouchEvent有关。看ViewGroup#dispatchTouchEvent，如果Button没有处理事件，就会开启下一个循环，currentZ会更小，事件就会流转到父容器的手里。如果父容器也不处理，那就继续向上return。
可是如果在for循环中，Button处理掉了事件，就会break，即终止了for循环，也就是终止了事件的分发，别人就处理不了了。所以如果Button一旦处理了，Button的父容器就拿不到这个事件了。
当Button处理完事件后，调用addTouchTarget方法：
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);target.next = mFirstTouchTarget;mFirstTouchTarget = target;return target;
}
意味着newTouchTarget==mFirstTouchTarget、alreadyDispatchedToNewTouchTarget = true
再往后，mFirstTouchTarget ！= null，走else：
// Button处理事件后，mFirstTouchTarget != null，进入elseif (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;//这个while循环内的操作，意味着while只会进去一次。while (target != null) {//next为nullfinal TouchTarget next = target.next;//alreadyDispatchedToNewTouchTarget就是true，上面刚刚给赋的值//两个条件都满足，即handled=true；while只循环一次，故退出循环后，直接就将handled = true返回了。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;//将null给到targettarget = next;}}
最后将handled返回就完事了。
滑动冲突
说起滑动冲突，我们都遇到过。ViewPager嵌套ListView，如果ViewPager的onInterceptTouchEvent return了true后，ListView的世界都坍塌了。
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;
}
是否执行onInterceptTouchEvent，取决于disallowIntercept是否为false。假设onInterceptTouchEvent被执行了，即intercepted=true，下面的if 就不会再走了：
//没拦截，就往里进了if (!canceled && !intercepted) {// If the event is targeting accessibility 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 downfinal 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;//newTouchTarget在上面没几行就置空了。//childrenCount 表示控件的个数，肯定不为0if (newTouchTarget == null && childrenCount != 0) {final float x = ev.getX(actionIndex);final float y = ev.getY(actionIndex);// buildTouchDispatchChildList：对子View根据currentZ进行排序final ArrayList<View> preorderedList = buildTouchDispatchChildList();final boolean customOrder = preorderedList == null&& isChildrenDrawingOrderEnabled();final View[] children = mChildren;//从数组最后面，currentZ最大的开始for (int i = childrenCount - 1; i >= 0; i--) {//先拿到View的下标final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);//根据下标，得到View（如：Button） final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex);if (childWithAccessibilityFocus != null) {if (childWithAccessibilityFocus != child) {continue;}childWithAccessibilityFocus = null;i = childrenCount - 1;}//拿到Button后，canViewReceivePointerEvents判断点击是否是动画、是否可见，//isTransformedTouchPointInView判断点击是否在View上。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);//dispatchTransformedTouchEvent负责将事件分发给谁来处理事件，return handled = child.dispatchTouchEvent(transformedEvent);//这意味这事件已经传递到View中了。//View#dispatchTouchEvent的返回结果--->result 只有当onTouchEvent处理后，result才为true。//换句话说，当Button处理了事件，才会命中这个if，break掉for循环；如果Button没处理，就开始下一次循环，取出比Button的currentZ值更小的父容器，将事件交给它。//Button处理事件就处理，Button不处理，就往上传递交给Button的父容器。如果父容器也不处理，那就交给父容器的父容器......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 indexfor (int j = 0; j < childrenCount; j++) {if (children[childIndex] == mChildren[j]) {mLastTouchDownIndex = j;break;}}} else {mLastTouchDownIndex = childIndex;}mLastTouchDownX = ev.getX();mLastTouchDownY = ev.getY();//Button处理事件后，调用addTouchTarget方法--->mFirstTouchTarget!=null--->newTouchTarget==mFirstTouchTargetnewTouchTarget = 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;}}}
这也就意味着，这个ViewGroup的多层子View们就不会有得到事件的机会了。从ViewGroup这就已经拦截了。
然后就往下走if，这里mFirstTouchTarget肯定为null，因为它在上面那一大段if里面的addTouchTarget方法内才被赋值。
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;//这个while循环内的操作，意味着while只会进去一次。while (target != null) {//next为nullfinal TouchTarget next = target.next;//alreadyDispatchedToNewTouchTarget就是true，上面刚刚给赋的值//两个条件都满足，即handled=true；while只循环一次，故退出循环后，直接就将handled = true返回了。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;//将null给到targettarget = next;}}还是会调用dispatchTransformedTouchEvent方法，但是参数有改变，child为null。这样就会走到dispatchTransformedTouchEvent方法的if中：
if (child == null) {handled = super.dispatchTouchEvent(transformedEvent);
} else {......
调用的是super的dispatchTouchEvent方法，并非else中的child.dispatchTouchEvent方法。即调用的是ViewGroup自己的dispatchTouchEvent方法。即这个事件由ViewGroup自己处理。这也是当重写的onInterceptTouchEvent方法返回true后，其包含的子View就不会滑动了的原因所在。
处理滑动冲突
1. 内部拦截法
即父容器不进行拦截，让子View进行拦截。如果子View需要该事件，就消耗掉。否则，就还给父容器处理。和分发机制有点区别，内部拦截法需要requestDisallowInterceptTouchEvent方法的配合才行（上面已经结合源码解释过了），还得重写子View的分发方法dispatchTouchEvent方法：
//内部拦截法@Overridepublic boolean dispatchTouchEvent(MotionEvent event) {int x = (int) event.getX();int y = (int) event.getY();switch (event.getAction()) {case MotionEvent.ACTION_DOWN: {getParent().requestDisallowInterceptTouchEvent(true);break;}case MotionEvent.ACTION_MOVE: {int deltaX = x - mLastX;int deltaY = y - mLastY;//父容器需要该事件if (Math.abs(deltaX) > Math.abs(deltaY)) {getParent().requestDisallowInterceptTouchEvent(false);}break;}case MotionEvent.ACTION_UP: {break;}default:break;}mLastX = x;mLastY = y;return super.dispatchTouchEvent(event);}
除此之外，父容器也得默认拦截除DOWN外的其他事件，只有这样，当子View调用getParent().requestDisallowInterceptTouchEvent(false)时，父容器才会继续拦截所需的事件。上面提到过，DOWN事件受标志位FLAG_DISALLOW_INTERCEPT控制。一旦父容器拦截DOWN事件，所有的事件就都无法传递到子元素中去了，内部拦截法也就成了“黄粱一梦”。
2.外部拦截法
即父容器进行拦截，如果父容器需要该事件就拦截，反之不拦截。外部拦截相比于内部拦截，更简单。外部拦截的做法，更符合事件分发机制。外部拦截法比较“省心”，只需要重写父容器的onInterceptTouchEvent方法即可：
@Overridepublic boolean onInterceptTouchEvent(MotionEvent event) {// 外部拦截法int x = (int) event.getX();int y = (int) event.getY();switch (event.getAction()) {case MotionEvent.ACTION_DOWN: {mLastX = (int) event.getX();mLastY = (int) event.getY();break;}case MotionEvent.ACTION_MOVE: {int deltaX = x - mLastX;int deltaY = y - mLastY;if (Math.abs(deltaX) > Math.abs(deltaY)) {return true;}break;}case MotionEvent.ACTION_UP: {break;}default:break;}return super.onInterceptTouchEvent(event);}
事件分发机制并不是洪水猛兽相关推荐
- View事件分发机制（源码 API27）
1.什么是事件分发机制 当用户触摸屏幕时,会产生一个touch事件,这个touch事件(motionEvent)传递到某个具体的view处理的整个过程 用户触摸屏幕会产生一个事件流(ACTION_DO ...
- Android事件分发机制详解
2019独角兽企业重金招聘Python工程师标准>>> 之前在学习Android事件方法机制的时候,看过不少文章,但是大部分都讲的不是很清楚,我自己理解的也是云里雾里,也尝试过阅读源 ...
- android触摸事件分发,Android 事件分发机制
Android 事件分发机制一直让人头痛,之前也是面向 GitHub 编程得过且过.今天下定决心了解一下,以便后面自己定制 View 效果.Android 触摸事件有三个基本类型:ACTION_DOW ...
- View事件分发机制（源码分析篇）
01.Android中事件分发顺序 1.1 事件分发的对象是谁 事件分发的对象是事件.注意,事件分发是向下传递的,也就是父到子的顺序. 当用户触摸屏幕时(View或ViewGroup派生的控件),将产 ...
- 【Android View事件分发机制】关于拦截事件的注意点
在父容器拦截事件时,为什么不能拦截DOWN事件呢? 先看看源码: 回顾一下事件分发机制原理,当事件来了之后,如果父容器不拦截,则会询问其child view ,当某child view 有事件需求,父 ...
- 【转】Android事件分发机制完全解析，带你从源码的角度彻底理解(下)
转载请注明出处:http://blog.csdn.net/guolin_blog/article/details/9153761 记得在前面的文章中,我带大家一起从源码的角度分析了Android中Vi ...
- Android ViewGroup事件分发机制
理~ 1.案例 首先我们接着上一篇的代码,在代码中添加一个自定义的LinearLayout: [java] view plaincopy package com.example.zhy_event03 ...
- Android View 事件分发机制详解
想必很多android开发者都遇到过手势冲突的情况,我们一般都是通过内部拦截和外部拦截法解决此类问题.要想搞明白原理就必须了解View的分发机制.在此之前我们先来了解一下以下三个非常重要的方法: di ...
- Android View的事件分发机制解析
作者:网易·周龙 最近刚看完android-Ultra-Pull-To-Refresh下拉刷新的源码,发现在写自定义控件时,对于View的事件的传递总是搞不太清楚,而View事件的分发机制,又是解决可 ...
最新文章
- java实现excel文件上传_java相关：SpringMVC下实现Excel文件上传下载
- luoguP1419 寻找段落(二分答案+单调队列）
- java佳沃维洛奇,新品速递：JAVA 双雄耀世登场
- 响应式布局框架 Pure-CSS 5.0 示例中文版-下
- xtrabackup实现数据备份与恢复
- 为什么我们需要Logstash,Fluentd等日志摄取器？
- linux 历史命令快捷键,Linux历史命令及bash快捷键
- 基于springboot+shiro一套可落地实施安全认证框架整合
- kettle系列-6.kettle实现多字段字典快速翻译
- HDU 2870 Largest Submatrix
- java可视化编程教程_JAVA可视化编程——SWING
- 《人间告白》---我看万物像你，我看你像万物
- 怎么修改照片文件的大小？教你一招改变图片大小尺寸
- 巴巴运动网学习笔记(76-80)
- 重装系统后怎么恢复数据？看完你就了解了
- 人数全球第一，但现在中国的问题不是人太多，而是太少 | 浪潮工作室
- web 前端常见英文汇总
- 百度AI入门课-day2作业
- 2月15日市场游资操作情况以及龙虎榜
- 如何做到数据分析报告（五）