作为程序猿，最不想 看的但是也不得不去看的就是源码！所谓知其然也要知其所以然，神秘的大佬曾经说过进阶的方法就是READ THE FUCKING CODE！
认识MotionEvent
负责集中处理所有类型设备的输入事件.我们对屏幕的点击，滑动，抬起等一系的动作都是由一个一个MotionEvent对象组成的。
主要事件类型
- ACTION_DOWN 手机初次触摸到屏幕事件
- ACTION_MOVE 手机在屏幕上滑动时触发,会回调多次
- ACTION_UP 手指离开屏幕时触发
主要方法
- getAction() 获取事件类型
- getX() 获取触摸点在当前View的X轴坐标
- getY() 获得触摸点在当前 View 的 Y 轴坐标
- getRawX() 获得触摸点在整个屏幕的 X 轴坐标
- getRawY() 获得触摸点在整个屏幕的 Y 轴坐标
上面这些是基本操作.下面我们来看一个小东西:
class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) btn_test.setOnTouchListener { v, event -> when (event.action) { MotionEvent.ACTION_DOWN -> { Log.e("xfhy", "ACTION_DOWN") } MotionEvent.ACTION_MOVE -> { Log.e("xfhy", "ACTION_MOVE") } MotionEvent.ACTION_UP -> { Log.e("xfhy", "ACTION_UP") } else -> { } } //返回false false } btn_test.setOnClickListener { Log.e("xfhy", "点击事件") } }}复制代码 最后执行结果是
2018-10-15 17:51:19.766 9257-9257/com.xfhy.clickdemo E/xfhy: ACTION_DOWN2018-10-15 17:51:19.785 9257-9257/com.xfhy.clickdemo E/xfhy: ACTION_MOVE2018-10-15 17:51:19.844 9257-9257/com.xfhy.clickdemo E/xfhy: ACTION_MOVE2018-10-15 17:51:19.844 9257-9257/com.xfhy.clickdemo E/xfhy: ACTION_UP2018-10-15 17:51:19.848 9257-9257/com.xfhy.clickdemo E/xfhy: 点击事件复制代码
onClick()是在ACTION_UP之后才调用的. 至于为什么,稍后会给出解释(源码就是这样写的).
MotionEvent事件分发
当一个MotionEvent产生后,需要分发给一个具体的View,去消化处理.我们需要去了解这个分发的过程.
下面有几个重要的方法,简单介绍一下:
- public boolean dispatchTouchEvent(MotionEvent event) 事件的分发.对于一个根ViewGroup来说,发生点击事件首先调用dispatchTouchEvent()
- public boolean onInterceptTouchEvent(MotionEvent ev) 事件拦截.如果这个ViewGroup的onIterceptTouchEvent返回true就表示它要拦截当前事件,接着这个ViewGroup的onTouchEvent就会被调用.如果onIterceptTouchEvent返回false,那么就会继续向下调用子View的dispatchTouchEvent方法.一旦一个元素拦截了某事件,那么一个事件序列里面后续的Move,Down事件都会交给它处理.并且它的onInterceptTouchEvent不会再调用.
- public boolean onTouchEvent(MotionEvent ev) 事件处理.View的默认实现会在onTouchEvent里面把touch事件解析成Click之类的事件.View的onTouchEvent默认都会消耗事件,除非它的clickable和longClickable都是false(不可点击),但是enable属性不会影响.
- 点击事件传递顺序 Activity -> Window -> View
下面是View事件分发流程图:
现在,我们队View的事件分发有了一个大致的了解.
上面的三个方法可以用以下伪代码来表示其关系:
public boolean dispatchTouchEvent(MotionEvent ev) { boolean consume = false;//事件是否被消费 if (onInterceptTouchEvent(ev)){ //调用onInterceptTouchEvent判断是否拦截事件 consume = onTouchEvent(ev);//如果拦截则调用自身的onTouchEvent方法 }else{ consume = child.dispatchTouchEvent(ev);//不拦截调用子View的dispatchTouchEvent方法 } return consume;//返回值表示事件是否被消费，true事件终止，false调用父View的onTouchEvent方法 }复制代码 通过上面的介绍,差不多简单了解了事件的传递机制.下面我们来看看源码:
源码分析
事件从最先到达Activity,我们来看一下Activity的dispatchTouchEvent()
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { //一个空方法,一般用于开发者想监听某个点击事件的开始 onUserInteraction(); } //交给Window去分发 if (getWindow().superDispatchTouchEvent(ev)) { return true; } //如果没人处理这个事件,那么当前Activity去处理 return onTouchEvent(ev);}复制代码 上面是getWindow().superDispatchTouchEvent(ev).交给Window去分发事件. 然后Window只有一个实现类PhoneWindow,其实最后就是调用的PhoneWindow中的superDispatchTouchEvent(ev).
### PhoneWindow部分代码private DecorView mDecor;@Overridepublic boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event);}复制代码 咦,,看到没有,其实是通过顶级View--DecorView去分发事件,嗯,很合乎常理.从上往下分配任务.
下面是DecorView的代码
public boolean superDispatchTouchEvent(MotionEvent event) { return super.dispatchTouchEvent(event); }复制代码 再跟进super.dispatchTouchEvent(event);,就来到了ViewGroup(显然,DecorView是ViewGroup).
public boolean dispatchTouchEvent(MotionEvent ev) { boolean handled = false; // 判断当前View是否没被遮盖住 如果是遮盖住了,则不进行事件分发 if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; //处理初次的按下事件 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. //在开始新的触摸手势时丢弃所有先前的状态。 cancelAndClearTouchTargets(ev); //重置所有触摸状态以准备新周期。 resetTouchState(); } //检测拦截 final boolean intercepted; //事件是按下 if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { //判断是否禁止拦截 当子View调用requestDisallowInterceptTouchEvent(true)之后,这里的disallowIntercept就是true->禁止拦截 因为子类想接收这个事件并处理自己的逻辑 final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { //子类没有禁止拦截 //是否需要拦截事件 子类可以实现onInterceptTouchEvent()去很轻松的实现事件拦截 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; } //检查是否已经被取消了 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; //如果没被取消 && 没有被拦截 if (!canceled && !intercepted) { 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; final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { final float x = ev.getX(actionIndex); final float y = ev.getY(actionIndex); // Find a child that can receive the event. // Scan children from front to back. final ArrayList preorderedList = buildTouchDispatchChildList(); final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder); final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex); // If 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; } // a.如果View不可见并且没有播放动画 // b.点击事件的坐标落在View的范围内 // 满足a或者b则不分发事件给这个view if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; } newTouchTarget = getTouchTarget(child); if (newTouchTarget != null) { //子View已经接收触摸事件在自己的范围内,则直接跳出循环,将事件给它自己处理. // 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); //这里实际上是去调用child的dispatchTouchEvent(event);->子类去分发事件. //ps: ViewGroup才能分发事件,View不能分发. if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { //子类想自己接收该事件(在自己的范围内) // 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(); //将child赋值给mFirstTouchTarget newTouchTarget = addTouchTarget(child, idBitsToAssign); alreadyDispatchedToNewTouchTarget = true; //如果某个child处理了事件,那么就不用继续循环了,直接跳出循环. 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) { //没有child接收该事件,则调用super.dispatchTouchEvent(event); 将该事件交给View去处理 // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); } return handled; } //在ViewGroup中，比View多了一个方法—onInterceptTouchEvent()方法，这个是干嘛用的呢，是用来进行事件拦截的，如果被拦截，事件就不会往下传递了，不拦截则继续。 //子类可以去实现这个方法,然后就可以轻松的拦截事件啦. public boolean onInterceptTouchEvent(MotionEvent ev) { if (ev.isFromSource(InputDevice.SOURCE_MOUSE) && ev.getAction() == MotionEvent.ACTION_DOWN && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY) && isOnScrollbarThumb(ev.getX(), ev.getY())) { return true; } return false; } /* 是否能收到事件: 如果可见或者没有播放动画 */ private static boolean canViewReceivePointerEvents(@NonNull View child) { return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null; }复制代码 上面是ViewGroup的分发事件源码,只抽取了源码的部分,关键部分加入了注释.
结论
ViewGroup会遍历所有子View去寻找能够处理点击事件的子View（可见，没有播放动画，点击事件坐标落在子View内部）最终调用子View的dispatchTouchEvent方法处理事件
当子View处理了事件则mFirstTouchTarget 被赋值，并终止子View的遍历。
如果ViewGroup并没有子View或者子View处理了事件，但是子View的dispatchTouchEvent返回了false（一般是子View的onTouchEvent方法返回false）那么ViewGroup会去处理这个事件（本质调用View的dispatchTouchEvent去处理）
下面来看一下View的dispatchTouchEvent()
public boolean dispatchTouchEvent(MotionEvent event) { ... boolean result = false; //如果窗口没有被遮盖 if (onFilterTouchEventForSecurity(event)) { if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) { result = true; } //noinspection SimplifiableIfStatement //监听事件 ListenerInfo li = mListenerInfo; //这里的li.mOnTouchListener.onTouch(this, event)是有返回值的,如果是返回了true,那么result就是true了. 相当于处理了触摸事件 if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { result = true; } //result为false时调用自己的onTouchEvent()去处理该事件. if (!result && onTouchEvent(event)) { result = true; } } ... return result; }复制代码 从上面的代码中可以看出,如果设置了OnTouchListener并且onTouch方法返回了true，那么onTouchEvent不会被调用。
我们来看看onTouchEvent()方法
public boolean onTouchEvent(MotionEvent event) { final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); //CLICKABLE和LONG_CLICKABLE任何一个都可以消费该事件 //TextView默认是clickable是false,Button默认是true //设置setOnClickListener()时会将clickable置为true //设置setOnLongClickListener()时会将longClickable置为true final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE; //即使View被设置成了不可用(setEnable(false)->DISABLED),但它还是可以消费点击事件 if ((viewFlags & ENABLED_MASK) == DISABLED) { if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) { setPressed(false); } mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; // A disabled view that is clickable still consumes the touch // events, it just doesn't respond to them. return clickable; } if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) { switch (action) { case MotionEvent.ACTION_UP: mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; if ((viewFlags & TOOLTIP) == TOOLTIP) { handleTooltipUp(); } if (!clickable) { removeTapCallback(); removeLongPressCallback(); mInContextButtonPress = false; mHasPerformedLongPress = false; mIgnoreNextUpEvent = false; break; } boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { // take focus if we don't have it already and we should in // touch mode. boolean focusTaken = false; if (isFocusable() && isFocusableInTouchMode() && !isFocused()) { focusTaken = requestFocus(); } if (prepressed) { // The button is being released before we actually // showed it as pressed. Make it show the pressed // state now (before scheduling the click) to ensure // the user sees it. setPressed(true, x, y); } if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // This is a tap, so remove the longpress check removeLongPressCallback(); // Only perform take click actions if we were in the pressed state if (!focusTaken) { // Use a Runnable and post this rather than calling // performClick directly. This lets other visual state // of the view update before click actions start. if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { //在ACTION_UP 方法发生时,会触发performClick()方法. performClick(); } } } .... } mIgnoreNextUpEvent = false; break; .... } return true; } return false; }复制代码 public boolean performClick() { final boolean result; final ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); //回调点击事件 li.mOnClickListener.onClick(this); result = true; } else { result = false; } sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); return result;}复制代码 所以,回调点击事件是在事件的最后Action_up中才去调用的.这也就解释了上面的demo中的最后才会调用回调点击事件的方法.
简单分析了一下View事件分发.希望能帮到大家.