事件分发流程简述
事件分发是从Activity开始,核心方法有三个,1.dispatchTouchEvent(事件分发方法) 2. onInterceptTouchEvent(事件拦截方法)3. onTouchEvent(事件处理方法),点击Activity后会调用decodeView dispatchTouchEvent方法, 然后事件分发流程如下边伪代码逻辑:
public boolean dispatchTouchEvent(MotionEvent event) {
boolean isConsume = false;
if (isViewGroup) {
if (onInterceptTouchEvent(event)) {
isConsume = onTouchEvent(event);
} else {
isConsume = child.dispatchTouchEvent(event);
}
} else {
//isView
isConsume = onTouchEvent(event);
}
return isConsume;
}
首先判断是否是viewGroup :
- 如果是viewGroup:判断是否拦截该事件;
如果拦截:则调用自身的onTouchEvent。
如果不拦截:则调用child的分发事件 - 如果是view:直接调用事件处理方法dispatchTouchEvent --> onTouchEvent
其实这个伪代码逻辑只体现了事件分发流程的一半逻辑,事件分发从上到下派发,但是执行顺序从下到上执行,而决定那个环节的view执行事件,取决于onTouchEvent方法的返回值,
- 如果返回false: 代表事件该view不会去消费, 则在接下来的事件中则不会去处理,因为父view在move事件中会主动拦截掉事件(因为子view已经通知父view我不会去处理该事件),所以接下来的事件将不会被分发给该view。
- 如果返回true:表示在该view中消费事件,则接下来的事件,均会交给该view处理,因为在move事件时,父view会发现已经有子view会处理事件,则直接将事件分发给该View。
上边是大概流程的逻辑,下边我会列举两个例子,提出两个思考,并通过源码进行分析讲解
首先我新建三个继承自LinearLayout的Viewgroup,代码如下:
class CustomLineLayoutA @JvmOverloads constructor(
context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : LinearLayout(context, attrs, defStyleAttr) {
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
"A(${ev?.action}): dispatchTouchEvent".log()
return super.dispatchTouchEvent(ev)
}
override fun onTouchEvent(event: MotionEvent?): Boolean {
"A(${event?.action}): onTouchEvent".log()
return false
}
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
"A(${ev?.action}): onInterceptTouchEvent".log()
return super.onInterceptTouchEvent(ev)
}
}
class CustomLineLayoutB @JvmOverloads constructor(
context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : LinearLayout(context, attrs, defStyleAttr) {
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
"B(${ev?.action}): dispatchTouchEvent".log()
return super.dispatchTouchEvent(ev)
}
override fun onTouchEvent(event: MotionEvent?): Boolean {
"B(${event?.action}): onTouchEvent".log()
return false
}
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
"B(${ev?.action}): onInterceptTouchEvent".log()
return super.onInterceptTouchEvent(ev)
}
}
class CustomLineLayoutC @JvmOverloads constructor(
context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : LinearLayout(context, attrs, defStyleAttr) {
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
"C(${ev?.action}): dispatchTouchEvent".log()
return super.dispatchTouchEvent(ev)
}
override fun onTouchEvent(event: MotionEvent?): Boolean {
"C(${event?.action}): onTouchEvent".log()
return true
}
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
"C(${ev?.action}): onInterceptTouchEvent".log()
return super.onInterceptTouchEvent(ev)
}
}
布局嵌套如下:
<com.czy.yq_wanandroid.test.CustomLineLayoutA
android:layout_width="match_parent"
android:layout_height="200dp"
android:background="@color/common_blue">
<com.czy.yq_wanandroid.test.CustomLineLayoutB
android:layout_width="match_parent"
android:layout_height="140dp"
android:background="#0ff"
>
<com.czy.yq_wanandroid.test.CustomLineLayoutC
android:background="@color/common_gray"
android:layout_width="match_parent"
android:layout_height="80dp"/>
</com.czy.yq_wanandroid.test.CustomLineLayoutB>
</com.czy.yq_wanandroid.test.CustomLineLayoutA>
情景一:默认情况 onTouch均为false时
根据前面总结,返回值均为false时,down事件时,分发流程正常,从A(dispatchTouchEvent)-> A(onInterceptTouchEvent) -> A(onInterceptTouchEvent)
B(dispatchTouchEvent)-> B(onInterceptTouchEvent) ->
C(dispatchTouchEvent) -> C(onInterceptTouchEvent) ->
C(onTouchEvent: false) -> B(onTouchEvent: false) -> A(onTouchEvent:)
在move 和up事件时,因为onTouchEvent 均返回false 将不会接受事件。
实际运行情况,日志打印如下:
2020-11-24 20:10:57.871 18316-18316/com.czy.yq_wanandroid D/YYYYYY: A(0): dispatchTouchEvent
2020-11-24 20:10:57.873 18316-18316/com.czy.yq_wanandroid D/YYYYYY: A(0): onInterceptTouchEvent
2020-11-24 20:10:57.874 18316-18316/com.czy.yq_wanandroid D/YYYYYY: B(0): dispatchTouchEvent
2020-11-24 20:10:57.875 18316-18316/com.czy.yq_wanandroid D/YYYYYY: B(0): onInterceptTouchEvent
2020-11-24 20:10:57.876 18316-18316/com.czy.yq_wanandroid D/YYYYYY: C(0): dispatchTouchEvent
2020-11-24 20:10:57.876 18316-18316/com.czy.yq_wanandroid D/YYYYYY: C(0): onInterceptTouchEvent
2020-11-24 20:10:57.878 18316-18316/com.czy.yq_wanandroid D/YYYYYY: C(0): onTouchEvent
2020-11-24 20:10:57.881 18316-18316/com.czy.yq_wanandroid D/YYYYYY: B(0): onTouchEvent
2020-11-24 20:10:57.882 18316-18316/com.czy.yq_wanandroid D/YYYYYY: A(0): onTouchEvent
思考一: 为什么均为false的时候只触发了down事件,而非down事件不会被触发
情景2 将B的onTouchEvent 方法改为true 其余不变
分析:在down事件时,一切流程正常进行
A(dispatchTouchEvent)-> A(onInterceptTouchEvent) ->
B(dispatchTouchEvent)-> B(onInterceptTouchEvent) ->
C(dispatchTouchEvent) -> C(onInterceptTouchEvent) ->
C(onTouchEvent: false) -> B(onTouchEvent: true, 此时A的OnTouchEvent不会触发)
//下边是move流程
-> A(dispatchTouchEvent)-> A(onInterceptTouchEvent) ->
B(dispatchTouchEvent)-> B(onTouchEvent: true)->
B(dispatchTouchEvent)-> B(onTouchEvent: true)->
B(dispatchTouchEvent)-> B(onTouchEvent: true)->.
....
实际打印结果
2020-11-24 21:22:00.576 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(0): dispatchTouchEvent
2020-11-24 21:22:00.577 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(0): onInterceptTouchEvent
2020-11-24 21:22:00.578 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(0): dispatchTouchEvent
2020-11-24 21:22:00.578 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(0): onInterceptTouchEvent
2020-11-24 21:22:00.579 20857-20857/com.czy.yq_wanandroid D/YYYYYY: C(0): dispatchTouchEvent
2020-11-24 21:22:00.579 20857-20857/com.czy.yq_wanandroid D/YYYYYY: C(0): onInterceptTouchEvent
2020-11-24 21:22:00.581 20857-20857/com.czy.yq_wanandroid D/YYYYYY: C(0): onTouchEvent
2020-11-24 21:22:00.582 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(0): onTouchEvent
2020-11-24 21:22:00.638 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): dispatchTouchEvent
2020-11-24 21:22:00.639 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): onInterceptTouchEvent
2020-11-24 21:22:00.641 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): dispatchTouchEvent
2020-11-24 21:22:00.642 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): onTouchEvent
2020-11-24 21:22:00.651 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): dispatchTouchEvent
2020-11-24 21:22:00.652 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): onInterceptTouchEvent
2020-11-24 21:22:00.653 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): dispatchTouchEvent
2020-11-24 21:22:00.655 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): onTouchEvent
2020-11-24 21:22:00.661 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): dispatchTouchEvent
2020-11-24 21:22:00.663 20857-20857/com.czy.yq_wanandroid D/YYYYYY: A(2): onInterceptTouchEvent
2020-11-24 21:22:00.664 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): dispatchTouchEvent
2020-11-24 21:22:00.666 20857-20857/com.czy.yq_wanandroid D/YYYYYY: B(2): onTouchEvent
源码分析(代码有删减)
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean handled = false;
//判断点击事件是否有效
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
//重点一:状态重置,在down事件时,重置之前的状态,并将mFirstTouchTarget = null; (mFirstTouchTarget!=null 表示是否有子view处理事件)
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// 重点二:事件拦截 拦截规则:
//1. down事件时,判断用户是否在子view中调用disallowIntercept 请求父容器不要拦截,若没有,则调用onInterceptTouchEvent进行拦截
//2. 非down事件时,若有子view处理事件(mFirstTouchTarget != null),同上逻辑,如果没有子view处理,则默认拦截
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 {
intercepted = true;
}
//是否是取消事件
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;
// 会在down事件找到处理事件的view时,被赋值为true
boolean alreadyDispatchedToNewTouchTarget = false;
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;
// 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<View> preorderedList = buildTouchDispatchChildList();
final View[] children = mChildren;
// 逆序遍历 寻找可以处理事件的view
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
//先直接获取处理事件的view,如果有,则直接退出循环
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
//重点三: 递归寻找可以处理事件的view
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
//将可以处理事件的view 赋值给newTouchTarget
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
if (preorderedList != null) preorderedList.clear();
}
}
}
// 重点四:如果没有处理事件的view,则调用自己的onTouchEvent方法
if (mFirstTouchTarget == null) {
// 其中dispatchTransformedTouchEvent第三个参数为null,则最终会走自身的onTouchEvent方法
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
//重点五: 如果找到处理事件的view
//分两种情况:1.down事件时(alreadyDispatchedToNewTouchTarget=true) :直接retrun true,结束分发事件,不进行分发,
//2. 非down事件时:将事件分发给该view
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
//down事件时直接return true
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//分发事件
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;
}
总结: viewGroup源码可以分为以下几部分
状态重置。 down事件时,首先设置mFirstTouchTarget==null,表示事件刚开始,清空消费事件的子view
判断是否拦截。(不考虑子view调用了requestDisallowInterceptTouchEvent)
a: 如果是down事件: 调用onInterceptTouchEvent决定是否拦截状态
b: 如果是非down事件且存在消费事件的子View(mFirstTouchTarget==null):调用onInterceptTouchEvent决定是否拦截状态
c: 其他情况: 设置为拦截状态寻找消费事件的view。down事件时,在不拦截状态下(其他情况不走该逻辑): 逆序循环view,调用dispatchTransformedTouchEvent递归查找能消费事件的view
a: 若找到返回true: mFirstTouchTarget 和newTouchTarget 都将不为Null,alreadyDispatchedToNewTouchTarget = true
b: 若找不到返回false: mFirstTouchTarget == null newTouchTarget == null进行事件分发。
A:若第3步没有找到消费view(mFirstTouchTarget ==null ):调用自身的onTouchEvent方法
B:若第3步找到了消费View:
a:如果是在down事件(alreadyDispatchedToNewTouchTarget = true):则直接返回true结束down事件的分发流程
b: 如果非down事件:则调用dispatchTransformedTouchEvent进行事件分发
下边来通过源码来解释下上面提出的两个问题:
思考一: 为什么均为false的时候只触发了down事件,而非down事件不会被触发
我们还是通过上边四个流程来解释
- down事件时执行时
Android事件开始是在Actvity开始执行,Activity内部最终是DecorView来进行分发,默认情况下和ABC三个Viewgroup返回状态一样,ViewGroup流程一致,均是下边流程
流程1:重置状态
流程2: 走2.a流程 且onInterceptTouchEvent未拦截,则拦截状态为:不拦截
流程3: 所有view的onTouchEvent方法均返回未false,则走3.b流程: mFirstTouchTarget == null newTouchTarget == null
流程4:走4.A流程,调用自身的onTouchEvent方法且返回false,
- move事件执行时
首先是DecorView
流程1. 非down时间 ,状态不重置
流程2: 非down事件,且未找到消费view,走2.c流程,拦截状态:拦截
流程3: 非down事件不走该流程,
流程4:因down事件时未找到消费view,则走4.A流程,分发流程直接返回true,不进行事件分发,故第一种情况下,则ABC三个Viewgroup打印结果只有down事件的日志
思考二:B的onTouchevent方法返回true后,A的onTouchEvent为什么不会执行了
主要原因是在流程4的时候走了4.B.a流程,直接返回了true结束down事件的分发流程,具体流程根据上面的流程分析即可。
大概流程如下:
down事件时: DecorView 将事件依次分发给 A->B->C 然后c返回了false给B,此时B将找不到消费事件的view(故在move事件时直接走不进行事件分发而是执行自己的onTouchEvent方法),而B返回了true给A,A于是就有了可消费事件的子View,然后return True,告知DecorView找到了消费的view 并结束事件。
move事件时: DecorView 有了可消费事件的view,所有会走4.B.b流程,进行事件分发给A,同理A也有可消费事件的View,走4.B.b流程进行事件给B,但是B没有可消费的View,所以直接走4.A ,调用自己的onTouchEvent方法,依次向上返回true,move的其中一个事件结束,接下来的move事件均按此流程执行