探究事件分发


为什么把握工作分发

面对滑动冲突时怎么处理,怎么自定义可双指扩大缩小的view,都需求把握工作分发的相关知识

首先在探求前,要理解什么是工作序列

什么是工作序列

一个完好的工作序列包含ACTION_DOWNACITON_MOVEACTION_UPACTION_CANCEK * % q 0 ] X O YL,由于包含多指操作,一切会包含ACTION_POINTER_DOWNACTION_POINTERV - 7 m _ I_UP

探究事件分发

还有一点,怎么符号被接触的view,而且仍是多指操作,经过TouchTarget

TouchTarget

TouchTarget的效果是用来符号被接l n x $ p触的view以及接触i= L ;d调集,是一个单向链表结构,ViewGroup中T H g : & m A( ( s * | =mFirstTouchTarget作为链表的头结点

其间比较重要的几个成员变量

  • public View child 表明被接触的子view
  • public int pointerIdBits 这个int值是用来符号被接触的id调集,由于是多指接触,而一个bit能够表明一个id,int是32bit,所以能够表明32个id

目标缓存池

由于整个接触过程中会不断的创立目标,所以内部实现了目标的缓存池,经过obtain获取目标,recycle缓存目标,

怎么工作分发

dispatchTransformedTouca p h ^ C N _hEvent办法效果:将一个motion event(工7 : g D c ]作序列)转换为特定子view的坐标,过滤掉无关的pR U r Oointer ids,假如有必要重写其action。假如cilid为空,则假定将此MotionEvent发送给此ViewGroup。
整个工作分发的核心在于ViewGroup的dispatchTouchEvent

dispatchTouchEvenr o = 1t

该办法V v X k k i c P k8 | x g q X s H实总共做了三件工作

  • 1.查看是否要阻拦工作分发
  • 2.假如不阻拦,就遍历子view,询问是否阻拦
  • 3.依据变量mFirstTouchTarget从头分发工作

下面,逐渐剖析下每步详细做了什么操作

1)查看是否= 0 b _ (要阻拦工作分发

            final boolean intercepted;
if (actionMasked == Mo) n R stionEvent.8 Q N Q L a  u *ACTION_DOWN
|| mFirstTouchTarget != null) {
//A
final boolean disallowIntercept = (mGroupFlags &0 6 s - FLAQ ^ e nG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action)9 & 4 j . M r;
} els1 , H O ye {
iK L f 5 O dntercepted = false;
}p 7 U U # Q ~ D
} else {
interf ; S a J p Ocepted = true;
}

注释A:该符号对应的requestDisallowInterceptTouchEvent办 ~ $ 7 & T +法,假如为tru] S b @e代表子view恳求父view不阻拦该工作,w X 8 n [ |假如不是子view恳求的不阻c D s拦的话,再有onInterceptTouchEvent判别是; a B ~ i ` t否阻拦

从这段逻辑也能够看出,假如down工作中阻拦了工作,那么整个工作序列都会交给其处理,除非子view恳求不要阻拦

2)假如不阻拦,就遍历子view,寻觅能够消费接触工作的子view

整个第# 2 6 `二步的核心,便是找到Tk [ D | 7 i AouchTarget

 if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign))K _ -  : j p {
...
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}

那假如找不到呢?就会将接触id添加到最近最少使用的target,才用头插( R O法添加到Toug $ h Q M V R !chTarget链表

第二步中还有个要害点,便是会依照层级的凹凸次K X r C ^序遍历子view,这也体现了常规的“所见即所得”的思维,即用户看到的最上面view的便是级别最高的

比如

<Linei 3 NarLa@ w # _ U Byout&Z @ Bgt;
<FrameLayout>
<TextView/>
</FrameLayout>
</LinearLayout>

对应的层级次序能够用下图表明

探究事件分发

3)依据变量mFirstTouchTarget从头分发工作

假如mFirstTouchTarget存在,则遍历Touchj o 4 b m | L S 6Tarf m 3 k M m @get,设置工作

假如mFirstTouchTarget不存在的话,就会将child置为null,传入dispatchTransformedTouchEvent,实践是将cancel封装成MotionEvent,传入自己的OnTouchEvent

其间还有需求留意的点,便是

 if (alreadyDispatw i % 1 ; kchedToNewTouchTarget && target == newTouc5  , S  / 1hTarget) {
handled = true;
} else {
//留意这个布尔值
fic c h m L P #nal boolean cancelChild = resetCancelNextUpFlag(target.ch} B ! ) ( j 6 0 5ild)
|| intercepted;
...
}

原本现已分发给子Y g i % 2 4 yview的工作,O A T s D父view会取消掉,那什么情况会触发这个判别呢?

有个经典的比如便是ScollViel i S w w U Lw内包裹Button,C n 2 @ X & ! +按住Button的时候持有这个工作,但是假如翻滚屏幕,这时候ScollView就$ ) a会抢占工作

工作分发的实质

整个工作分发的过程中,会从上到下查看是否需求阻拦工作,不论阻拦不阻拦,都会逐级上报,把阻拦成果告诉上层,实践体现的是递归的思路

探究事件分发

参考

  • 彻底把握 Android touch 工作分发时序
  • 理解工作分发的实质引荐:] b / h ) u $重学安卓:学习 View 工作h J d分发,就像外地人上了黑车!
  • Android工作分发机制

附完好释义

View. e $ v ^ v W rGruop#dispatchTop Y : h e j i 8uchEvent

@Override
public boolean dispatchTk ] = c { p 8 youchEvent(MotionEvent ev) {
if (mInputEveI y , d R 7 b ( 6ntConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1)r A W % | T X;
}
//分发前的准备工作
if (ev.isTargetAccessiba X s G # ? : C :ilityFocus() && isAccessibilityFG - | { g ` `ocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(fals} F me);
}
boolean haD k hndled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = eK & ( E  *v.getAction();
final int actionMaskea N ? 6 f | = Vd = action & MotionEvent# S ` g.ACTION_MASK;
// 处理初始down工作
if (actionMasked == MotionEvent.ACTIOo h _ J y ] T O *N_DOWN) {
//重置之前的接触手势
ca* . ,ncelAndClearTouchTargets(ev);
resetTouchState(. : w % l);
}
// 查看是否阻拦工作
final bool6 ,  ; ~ =ean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget !h 9 L r ~= null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction= f j(action); // 保存action
} ec | @ ) g S 4 :lse {
intercepted = false;
}
} else {
//接触view不存在或许不是开端的down工作,所以view group会继续阻拦工作
intercepted = true;
}
//假如现已阻拦或许有view捕获3 w *了手势,就开端正常的工作分发。
if (intercepted || mFirstTouchTarget != null) {
ev.setTarge. J U J z TtAccessibilityFocus(false);
}
//查看是否是cF j 6 D 0 0 Y kancel工作
finalF t f m k boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// 更新包含多指操作down工作的touch target
final bs ~ joolean spliG C @t = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled &&am& } S Zp; !intercepted) {
View childWithAccessibilityFocus = ev.isT3 6 4argetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEve = Bnt.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionInde1 a ) 2 |x(); // always 0 for down
final int idBitsToAssign[ U @ ? o x i G =M 7 T o + split ? 1 << ev.getPointerd $ L * nId(act3 h L ~ eionInd` = R { e :ex)
: TouchTargeM 4 ^ T * U 9 1t.ALL_POINTER_IDS;
//铲除早期该接触id的touch targetn W j c 9 D / t O,防止数据不同步M = ]
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && children% W % O 9 5Count != 0) {
final float x =b  F ev.getX(actionIndex);U L ^ R 8 w y K
final float y = ev.getY(actionIndex);
//从层级高的到层级低的,逐级遍历,查找能够接受工作的子view
final ArrayList<View> preorderedList = buildTouchDispatchChij Z : $ D 2ldList();
final boolean} K W K E { custF 1 q l , &omOrder =) 1 6 ] preord% S z C f [ W ( deredH } / SList == nulA i ] q h ~ cl
&am9 0 g * 3 rp;& isChildrenDrawin$ & n KgOr} D S ? G ) P EderEnabled();
fiC } v C = M [ nal VieZ * u a 6w[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex0 % n T  i U 8 = getAndVerifyPreordereJ y ) 0 S # F p ddIndex(
childrenCount, i, cu| M @ %stomOrder);
final View child = getAndVerifyPreorderedVj e /iew(
preordz ` P ueredList, children, childIndex);
if (childWithAccessibilityr S c ` Z ` 8 DFocuP i [ _ ) *s != null) {
if (childWithAccessibil& z 1ityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!child.canReceivePointerEvents()
|| !isTh l 7 kransformedTouchPointIn& , + ) _ T i R ZView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
//子view在范围之内接纳到了接触工作,更新接触id,除了之前现已持有的接触id还需求添加接触id
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUp0 ] { 3 u Q 6Flag(child);
if (dispatck , w ShTransformedTouchEvent(ev, false, child, iY ~ D ZdBitsToAssign)) {
//子view想要接纳接触工作
mLastTouM  L P 4chDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find originn ` e u wak Z . ol index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownB & L nIndex = childIndex;
}
mLastTouchDownX = ev* ; B A C h ! o E.getX();
mLastTouchDownY = eL U ]v.getY();
nd x . ) k * ? g vewTouchTa: N # ,rget = af  @ddTouchTar} d D + c 5 ^ tget(child, idBitsToAssign);
alreadyDispatchedToNewTouc8 w # ( %hTarget = true;
break;
}
ev.setTargetAccessibilityFocus(false);
}
if (pre# ( OorderedList != null) pr` f l t M # } +eorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
//没有找到能够接纳接触工作的子view,则将接触id添加到最近最少使用的target
newTouchTarget = m, E + p Q J : tFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = neY t ` ? fwTouchTargetQ j X.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// 依据mFirstTouchTarget的值分发工作
if0 o A X 0 (mFirstTouchTarget == null) {
//假如没有, x F ktouch targets,& . x m C则将此ViewGroup作为普通view
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
//分p x 5 u ) R [ B H发给touch targets,但是要排除去现已分发过的target touch。必要情况下,取消to2 v m I Ouch targets的分发
TouchTarget predecessor = null;
TouchTarget target = mFirst] U ,TouchTarget;
while (target != null) {
fL 9 ` A w P gi2 Q O 4 * , - [ -nal TouchTarget next = target.next;
if (alreadyDispatchedToNes X KwTouchTarget &&B x J $ { e M l R; target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = rZ T K :esetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTc b H O 7 A x O EransformedTouchEvent(ev, cancelChil| B a h =dm $ A,
target.child, target.pointerIdBi# m lts)) {
handled = true;
}
i- & d A { af (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
}P A P z + 7 O h else {
predecessor.next = next;
}
targetn ( / z Z.reg s n mcyc+ Y i [ $ 2 e dle();
target = next;
continue;
}
}
predecessor = target;
ta( f @ 1 ! c m 4 $rget = next;
}
}
// 更新up或许cancel工作
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| acti( i & | Y Q t ( oonMasked == Moti5 ) + Y konEvent.ACTION_HOVER_MOVE)8  z {
resep N o ^ b $ P FtTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemo/ ]  Y ` C *ve = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTap [ ! p v B a , 4rgets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyV) E ` - h Aerifier.onUnhan5 & * V N ) 9dledEvent(ev, 1);
}
return handled;
}

V) Q | c | g FiewGroup#requestDisallowInterceptTouC ] ZchEvent

requestDisallowIR A P snterceptTouchEvent办法效果:t* ) J y # } ] A [ure表明子view不想让其父view在履行onInterceptTouchEvent阻拦工作。本父vie, 2 Y –w会逐s f s级往上传递。这个parent在N W 9 [ u j u呼应接触期间,必须履行chlid的恳求(也便是说,只会在parent接纳到up或许cancel时,铲除符号,对应的符号为FLAG_DISALLOy + F } nW_INTEC x 9 2 x 5 P H +RCEPT

ViewGroup#onInterceptTouchEvent

    public boolean onInteg m P Q N W z P CrceptTouchEvent(MotionEvent ev) {
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev* E L 9 T.getAction() == MotionEvent.AC@ E kTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrol. c & R W f 4 @lbarThumb(ev.getX(), ev.getY())) {
return true;
}
return false;
}

效果:用来阻拦一切的屏幕接触工作,能够在分发给chlid时查看工作,并且在任何时刻把握当时手势的一切权。

ViewGroup#dispatchTransformedTouchEvent

将接触工作转换为特定子view的坐标空间

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