ViewGroup與View
ViewGroup和View事件的分發，攔截，消費的相關方法如下表：
| 型別 | 相關方法 | ViewGroup | View |
|---|---|---|---|
| 事件分發 | dispatchTouchEvent | 有 | 有 |
| 事件攔截 | onInterceptTouchEvent | 有 | 無 |
| 事件消費 | onTouchEvent | 有 | 有 |
這個三個方法的返回值均是Boolean型別，通過true和false來控制事件的傳遞和消費流程。我們先通過實際例子來看看事件傳遞，消費的流程。
xml：
<?xml version="1.0" encoding="utf-8"?>
<com.aoy.touch.TouchViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.aoy.touch.MainActivity">
<com.aoy.touch.TouchChildView
android:layout_width="150dp"
android:layout_height="150dp"
android:background="@color/colorPrimary"
android:text="TouchChild"
android:gravity="center"
android:textSize="16sp"
android:textColor="#ffffff"
android:layout_centerInParent="true"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</com.aoy.touch.TouchViewGroup>
複製程式碼TouchViewGroup：
class TouchViewGroup : RelativeLayout {
val TAG : String = "TouchStudy"
constructor(ctx: Context):super(ctx)
constructor(ctx: Context,attrs: AttributeSet):super(ctx,attrs)
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
when(ev!!.action){
MotionEvent.ACTION_DOWN -> {
Log.i(TAG,"ParentView dispatchTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG,"ParentView dispatchTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP,MotionEvent.ACTION_CANCEL ->{
Log.i(TAG,"ParentView dispatchTouchEvent ACTION_CANCEL")
}
}
var ret = super.dispatchTouchEvent(ev)
Log.i(TAG,"ParentView dispatchTouchEvent return :" + ret)
return ret
}
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
when(ev!!.action){
MotionEvent.ACTION_DOWN -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_MOVE")
// return true
}
MotionEvent.ACTION_UP,MotionEvent.ACTION_CANCEL ->{
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_CANCEL")
}
}
var ret = super.onInterceptTouchEvent(ev)
Log.i(TAG,"ParentView onInterceptTouchEvent return :" + ret)
return ret
}
override fun onTouchEvent(event: MotionEvent?): Boolean {
when (event!!.action) {
MotionEvent.ACTION_DOWN -> {
Log.i(TAG, "ParentView onTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG, "ParentView onTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
Log.i(TAG, "ParentView onTouchEvent ACTION_CANCEL")
}
}
var ret = super.onTouchEvent(event)
Log.i(TAG,"ParentView onTouchEvent return :" + ret)
return super.onTouchEvent(event)
}
}
複製程式碼TouchChildView：
class TouchChildView : TextView {
val TAG : String = "TouchStudy"
constructor(ctx: Context): super(ctx)
constructor(ctx: Context,attrs: AttributeSet): super(ctx,attrs)
override fun dispatchTouchEvent(event: MotionEvent?): Boolean {
when(event!!.action){
MotionEvent.ACTION_DOWN -> {
Log.i(TAG,"ChildView dispatchTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG,"ChildView dispatchTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP,MotionEvent.ACTION_CANCEL ->{
Log.i(TAG,"ChildView dispatchTouchEvent ACTION_CANCEL")
}
}
var ret : Boolean = super.dispatchTouchEvent(event)
Log.i(TAG,"ChildView dispatchTouchEvent return :" + ret)
return ret
}
override fun onTouchEvent(event: MotionEvent?): Boolean {
when (event!!.action) {
MotionEvent.ACTION_DOWN -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_CANCEL")
}
}
var ret : Boolean = super.onTouchEvent(event)
Log.i(TAG,"ChildView onTouchEvent return :" + ret)
return ret
}
}
複製程式碼TouchViewGroup與TouchChildView主要是將接收到的事件列印出來。
TouchStudy: ParentView dispatchTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent return :false
TouchStudy: ParentView onTouchEvent ACTION_DOWN
TouchStudy: ParentView onTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
複製程式碼其事件的分發消費流程如下圖 :
由於childView在onTouchEvent()中沒有消耗down事件導致childView dispatchTouchEvent返回false,這會讓ParentView不會把後續的ACTION_MOVE和ACTION_UP分發給childView。同理由於childView和parentView的onTouchEvent()都沒有消耗down事件，所以parentView也沒有收到後續的ACTION_DOWN和ACTION_UP事件。
② 現在我們讓childView的onTouchEvent()消耗ACTION_DOWN事件,但ViewGroup中不攔截ACTION_DOWN事件，改動程式碼如下：
/**
* childView onTouchEvent
*/
override fun onTouchEvent(event: MotionEvent?): Boolean {
when (event!!.action) {
MotionEvent.ACTION_DOWN -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_DOWN")
return true
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_CANCEL")
}
}
var ret : Boolean = super.onTouchEvent(event)
Log.i(TAG,"ChildView onTouchEvent return :" + ret)
return ret
}
複製程式碼在childView中滑動之後，其log為：
TouchStudy: ParentView dispatchTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent return :true
TouchStudy: ChildView dispatchTouchEvent return :true
TouchStudy: ParentView dispatchTouchEvent return :true
TouchStudy: ParentView dispatchTouchEvent ACTION_MOVE
TouchStudy: ParentView onInterceptTouchEvent ACTION_MOVE
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_MOVE
TouchStudy: ChildView onTouchEvent ACTION_MOVE
TouchStudy: ChildView onTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent ACTION_MOVE
TouchStudy: ParentView onInterceptTouchEvent ACTION_MOVE
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_MOVE
TouchStudy: ChildView onTouchEvent ACTION_MOVE
TouchStudy: ChildView onTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent ACTION_CANCEL
TouchStudy: ParentView onInterceptTouchEvent ACTION_CANCEL
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_CANCEL
TouchStudy: ChildView onTouchEvent ACTION_CANCEL
TouchStudy: ChildView onTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
複製程式碼 其ACTION_DOWN事件的分發,消費流程圖如下：
其ACTION_MOVE和ACITON_UP（ACTION_CANCEL）事件的分發，消費入下圖:
③ 讓ViewGroup中攔截ACTION_DOWN事件，改動程式碼如下：
/**
* parentView onInterceptTouchEvent
*/
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
when(ev!!.action){
MotionEvent.ACTION_DOWN -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_DOWN")
return true;
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_MOVE")
// return true
}
MotionEvent.ACTION_UP,MotionEvent.ACTION_CANCEL ->{
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_CANCEL")
}
}
var ret = super.onInterceptTouchEvent(ev)
Log.i(TAG,"ParentView onInterceptTouchEvent return :" + ret)
return ret
}
/**
* childView onTouchEvent
*/
override fun onTouchEvent(event: MotionEvent?): Boolean {
when (event!!.action) {
MotionEvent.ACTION_DOWN -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_DOWN")
Log.i(TAG,"ChildView onTouchEvent return :" + true)
return true
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_CANCEL")
}
}
var ret : Boolean = super.onTouchEvent(event)
Log.i(TAG,"ChildView onTouchEvent return :" + ret)
return ret
}
複製程式碼這種情景下的執行log如下：
TouchStudy: ParentView dispatchTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent ACTION_DOWN
TouchStudy: ParentView onTouchEvent ACTION_DOWN
TouchStudy: ParentView onTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
複製程式碼ACTION_DOWN事件的分發消費流程圖：
這種情況下,parentView不會將任何事件分發給childView,同時parentView也沒有消費ACTION_DOWN事件，導致parentView不會收到ACTION_MOVE,ACTION_UP等事件。
④ 讓childView消耗ACTION_DOWN事件，同時讓ViewGroup中攔截ACTION_MOVE事件，改動程式碼如下：
/**
* parentView onInterceptTouchEvent
*/
override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
when(ev!!.action){
MotionEvent.ACTION_DOWN -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_DOWN")
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_MOVE")
return true
}
MotionEvent.ACTION_UP,MotionEvent.ACTION_CANCEL ->{
Log.i(TAG,"ParentView onInterceptTouchEvent ACTION_CANCEL")
}
}
var ret = super.onInterceptTouchEvent(ev)
Log.i(TAG,"ParentView onInterceptTouchEvent return :" + ret)
return ret
}
/**
* childView onTouchEvent
*/
override fun onTouchEvent(event: MotionEvent?): Boolean {
when (event!!.action) {
MotionEvent.ACTION_DOWN -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_DOWN")
Log.i(TAG,"ChildView onTouchEvent return :" + true)
return true
}
MotionEvent.ACTION_MOVE -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_MOVE")
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
Log.i(TAG, "ChildView onTouchEvent ACTION_CANCEL")
}
}
var ret : Boolean = super.onTouchEvent(event)
Log.i(TAG,"ChildView onTouchEvent return :" + ret)
return ret
}
複製程式碼其執行log如下：
TouchStudy: ParentView dispatchTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent ACTION_DOWN
TouchStudy: ParentView onInterceptTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent ACTION_DOWN
TouchStudy: ChildView onTouchEvent return :true
TouchStudy: ChildView dispatchTouchEvent return :true
TouchStudy: ParentView dispatchTouchEvent return :true
TouchStudy: ParentView dispatchTouchEvent ACTION_MOVE
TouchStudy: ParentView onInterceptTouchEvent ACTION_MOVE
TouchStudy: ChildView dispatchTouchEvent ACTION_CANCEL
TouchStudy: ChildView onTouchEvent ACTION_CANCEL
TouchStudy: ChildView onTouchEvent return :false
TouchStudy: ChildView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent ACTION_MOVE
TouchStudy: ParentView onTouchEvent ACTION_MOVE
TouchStudy: ParentView dispatchTouchEvent ACTION_CANCEL
TouchStudy: ParentView onTouchEvent ACTION_CANCEL
TouchStudy: ParentView onTouchEvent return :false
TouchStudy: ParentView dispatchTouchEvent return :false
複製程式碼ACTION_DOWN事件的分發消費過程圖:
ACTION_MOVE的分發消費過程圖：
從③和④兩種情況可以看出當parentView攔截ACTION_DOWN事件後，childView將不會收到ACTION_DOWN事和後續的ACTION_MOVE與ACTION_UP事件，而parentView能否收到後續的事件，取決於parentView的onTouchEvent是否消費ACTION_DOWN事件。當childView消費了ACTION_DOWN事件後，如果parentView攔截ACTION_MOVE事件，則後續的一系列事件都將交由parentView的ontouchEvent()來處理,不會再走onInterceptionEvent()方法，childView將不會收到後續的任何事件。
結論：
(1)不管是GroupView還是View,消費事件指的是消費ACTION_DOWN事件，只有消費了ACTION_DOWN事件，才有可能接收分發後續的ACTION_MOVE和ACTION_UP等事件。
(2)對於View而言，消耗ACTION_DOWN事件只有一種途徑：在onTouchEvent()中接受到ACTION_DOWN時返回true。 而GroupVie消耗ACTION_DOWN事件有兩種途徑：①其child view消費ACTION_DOWN;②其自身消耗ACTION_DOWN事件，即在其自身的onTouchEvent()中接受到ACTION_DOWN事件時返回true,這兩種消耗ACTION_DOWN事件的關係為：parentView會先view是否消耗ACTION_DOWN分發給child view，讓child view決定是否消耗ACTION_DOWN,只有當child view不消耗時，才將ACTION_DONW事件傳遞給其本身的onTouchEvent()方法讓其判斷是否消費ACTION_DOWN方法。
(3)當GroupView攔截某一事件時，GroupView 不會將這一事件和後續的所有事件分發給child view，攔截的這一事件將會交給GroupView的onTouchEvent()處理。對於後續GroupView接收到的所有事件不會走攔截過程，而是直接交由GroupView的onTouchEvent()處理。
原始碼分析
以下所有的原始碼都是基於API26（android 8.0）
View 的dispatchTouchEvent原始碼：
public boolean dispatchTouchEvent(MotionEvent event) {
...
if (onFilterTouchEventForSecurity(event)) {
//關注點一：當View為可點選並且在拖動scrollBar時直接消費事件
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//關注點二：當View設定為可點選並且並且設定OnTouchListener處理時，直接消費事件，並將所有的一系列事件交由OnTouchListener處理
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//關注點三：如果不是拖動scrollBar並且沒有設定OnTouchListener則事件交由onTouchEvent()處理
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
複製程式碼從“關注點二”和“關注點三”中可以看出如果View設定了OnTouchListener則view直接消費事件，並將所有的事件都交由OnTouchListener處理，就onTouchEvent()什麼事了，如果沒有設定OnTouchListener，則是否消費事件由onTouchEvent（）決定，下面看看View的onTouchEvent()原始碼。onTouchEvent原始碼較長，挑重點來看
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
...
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
...
break;
case MotionEvent.ACTION_DOWN:
...
break;
case MotionEvent.ACTION_CANCEL:
...
case MotionEvent.ACTION_MOVE:
...
break;
}
return true;
}
return false;
}
複製程式碼View的onTouchEvent()比較好理解，如果View設定為可點選或設定OnLongClickListener，OnClickListenerView就消費了事件。switch裡的程式碼是具體處理長按監聽和點選事件等事情。
GroupView的dispatchTouchEvent()就比較複雜了，下面通過關鍵原始碼來看看GroupView是如何分發消費事件的。
public boolean dispatchTouchEvent(MotionEvent ev) {
...
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
if (actionMasked == MotionEvent.ACTION_DOWN) {
//關注點一：接收到ACTION_DOWN事件時，將mFirstTouchTarget設定為 null
cancelAndClearTouchTargets(ev);
resetTouchState();
}
final boolean intercepted;
//關注點二：當處理ACTION_DOWN或mFirstTouchTarget不為空是走攔截流程
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget不為空是走攔截流程 != null) {
/*關注點三：是否不允許攔截事件，當child View呼叫
parent.requestDisallowInterceptTouchEvent()時，disallowIntercept = true*/
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;
}
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
...
/*關注點四：只有當事件為ACTION_DOWN或者為多點觸控的ACTION_POINTER_DOWN或者滑鼠懸浮事件時，
才會去在child view中尋找消費事件的view*/
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex();
//識別手指的標誌位
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
/*關注點五：先根據Z軸方法z座標值大小排序，(Z軸是三維座標系裡的Z方向，cardView設定陰影是就是設定Z軸的值)，
再根據child view的繪製順序排序*/
final ArrayList<View> 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);
...
//關注點六：如果child view 不可見，並且事件不是發生在child view的範圍內直接跳出查詢下一個child view
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
//關注點七：如果找到處理這一事件的child view,給mFirstTouchTarget賦值。
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();
//關注點八：給mFirstTouchTarget賦值
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
...
}
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;
}
}
}
// 關注點九：如果沒有找到child view去消費事件，將事件分發給自己，判斷是否消費事件
if (mFirstTouchTarget == null) {
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
//遍歷mFirstTouchTarget這個連結串列
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
/* 關注點十：如果child view消耗事件，判斷是否攔截事件，如果攔截事件則child view 將不會收到這次事件，而是收到
ACTION_CANCEL事件，而mFirstTouchTarget最終將會賦值為null;如果不攔截事件，則按正常流程將事件分發給child view */
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;
}
}
/*關注點十一：當接受到的事件時ACTION_UP，ACTION_CANCEL事件時，將
mFirstTouchTarget設定為null,重置FLAG_DISALLOW_INTERCEPT位*/
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;
}
複製程式碼- 重點關注下mFirstTouchTarget這個物件，mFirstTouchTarget是一個連結串列結構的物件，正常情況下這個連結串列只有一個元素，當GroupView允許處理多點觸控事件時，並且多點觸控發生時mFirstTouchTarget可能會有多個元素。多點觸控事件的分發消費流程與單點觸控的流程相似，下面的說明都是以單點觸控為例說明。
- ‘關注點五’註釋的程式碼說明了ACTION_DOWN事件是按照child view繪製順序來分發事件的，先繪製的child view會優先收到ACTION_DOWN事件。
- ‘關注點四’到‘關注點九’之間的程式碼就是ACTION_DOWN事件的分發消費過程。如果child view消費了ACTION_DOWN事件，在‘關注點八’的程式碼就給mFirstTouchTarget賦值，否則mFirstTouchTarget為null。
- ‘關注點九’說明如果child view沒有消費ACTION_DOWN事件，其是絕對不會接受到後續的ACTION_MOVE,ACTION_UP等事件,換句話說view消費事件指的是是否消費ACTION_DOWN事件。至於消費了ACTION_DOWN事件之後，能否接受到後續的事件，就要看paren view是否攔截事件了。
- ‘關注點十’程式碼是mFirstTouchTarget的遍歷過程，如果parentView攔截了事件，則child view會收到ACITON_CANCEL事件，同時mFirstTouchTarget會通過連結串列的遍歷會最終賦值為null,這回導致後續的事件不會分發給child view而是執行‘關注點九’的程式碼。
下面是dispatchTransformedTouchEvent（）的程式碼分析。
//當事件由GroupView自己處理則child = null
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
final int oldAction = event.getAction();
//當GroupView攔截事件時cancel = true
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
//GroupView自己處理事件。 GroupView繼承製View，super.dispatchTouchEvent就是呼叫View.dispatchTouchEvent
handled = super.dispatchTouchEvent(event);
} else {
//將事件分發給child view處理
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
// 獲取此次事件的所有手指標識位|運算值{@link MotionEvent#getPointerIdBits()}
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
//如果此次事件不合法，不處理
if (newPointerIdBits == 0) {
return false;
}
final MotionEvent transformedEvent;
//單點觸控處理
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 {
//多點觸控處理
transformedEvent = event.split(newPointerIdBits);
}
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);
}
transformedEvent.recycle();
return handled;
}
複製程式碼事件從activity到child view的完整分發消費圖：
