一、Android?touch事件的相關概念

用戶的Touch事件被包裝成MotionEvent

用戶當前的touch事件主要類型有：

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ACTION_DOWN: 表示用戶開始觸摸.

?ACTION_MOVE: 表示用戶在移動(手指或者其他)

?ACTION_UP:表示用戶抬起了手指?

ACTION_CANCEL:表示手勢被取消了,一些關于這個事件類型的討論見:http://stackoverflow.com/questions/11960861/what-causes-a-motionevent-action-cancel-in-android?

ACTION_OUTSIDE: 表示用戶觸碰超出了正常的UI邊界.

ACTION_POINTER_DOWN:有一個非主要的手指按下了.

ACTION_POINTER_UP:一個非主要的手指抬起來了

touch事件的元數據包括：

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touch的位置

手指的個數

touch事件的時間

一個touch手勢被定義為以ACTION_DOWN開始和以?ACTION_UP結束。

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二、Touch事件的處理流程

當用戶觸摸屏幕時，觸發Activity調用dispatchTouchEvent

事件對象會按自頂向下的順序在View Tree中傳遞

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? ? ?父View（ViewGroups）會調用dispatchTouchEvent將Event傳遞給子View ? ?

? ? Event在任何時候都可能被攔截

事件流會順著View鏈遞歸向下傳遞直到被消耗

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若某個View想處理touch事件，必須先消耗ACTION_DOWN。考慮到效率，后續的事件將不會向下傳遞。

若某個事件未被消耗，最后會被Activity的onTouchEvent()消耗

若任何View或ViewGroup設置了OnTouchListener，touch事件將被攔截。

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Activity.dispathcTouchEvent()的源碼分析：

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[java]?view plaincopy

/**?

????*?Called?to?process?touch?screen?events.?You?can?override?this?to?

????*?intercept?all?touch?screen?events?before?they?are?dispatched?to?the?

????*?window.?Be?sure?to?call?this?implementation?for?touch?screen?events?

????*?that?should?be?handled?normally.?

????*?

????*?@param?ev?The?touch?screen?event.?

????*?

????*?@return?boolean?Return?true?if?this?event?was?consumed.?

????*/??

???public?boolean?dispatchTouchEvent(MotionEvent?ev)?{??

???????if?(ev.getAction()?==?MotionEvent.ACTION_DOWN)?{??

???????????onUserInteraction();??

???????}??

???????if?(getWindow().superDispatchTouchEvent(ev))?{??

???????????return?true;??

???????}??

???????return?onTouchEvent(ev);??

???}??

由代碼可以看出，對于應用層，該函數在touch事件發生后首先被調用。onUserInteraction()是一個空函數，可被用戶重載以進行相關處理。Event隨后將被傳遞到關聯到root view的window。若子view消耗了該Event，則返回true，否則Event最后被Activity的onTouchEvent()消耗。

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ViewGroup.dispatchTouchEvent()的源碼分析如下：

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[java]?view plaincopy

public?boolean?dispatchTouchEvent(MotionEvent?ev)?{??

????????if?(mInputEventConsistencyVerifier?!=?null)?{??

????????????mInputEventConsistencyVerifier.onTouchEvent(ev,?1);??

????????}??

????????boolean?handled?=?false;??

????????if?(onFilterTouchEventForSecurity(ev))?{??

????????????final?int?action?=?ev.getAction();??

????????????final?int?actionMasked?=?action?&?MotionEvent.ACTION_MASK;??

????????????//?處理初始的down事件??

????????????if?(actionMasked?==?MotionEvent.ACTION_DOWN)?{??

????????????????//當新開始一個touch事件時，拋棄先前的touch狀態??

????????????????//當app切換，發生ANR或一些其他的touch狀態發生時，framework會丟棄或取消先前的touch狀態??

????????????????cancelAndClearTouchTargets(ev);??

????????????????resetTouchState();??

????????????}??

????????????//?檢查是否進行事件攔截??

????????????final?boolean?intercepted;??

????????????if?(actionMasked?==?MotionEvent.ACTION_DOWN??

????????????????????||?mFirstTouchTarget?!=?null)?{??

????????????????final?boolean?disallowIntercept?=?(mGroupFlags?&?FLAG_DISALLOW_INTERCEPT)?!=?0;??

????????????????if?(!disallowIntercept)?{??

????????????????????//回調onInterceptTouchEvent()，返回false表示不攔截touch，否則攔截touch事件。??

????????????????????intercepted?=?onInterceptTouchEvent(ev);??

????????????????????ev.setAction(action);?//?restore?action?in?case?it?was?changed??

????????????????}?else?{??

????????????????????intercepted?=?false;??

????????????????}??

????????????}?else?{??

????????????????//沒有touch事件的傳遞對象，同時touch動作不是初始動作down，所以ViewGroup繼續攔截事件??

????????????????intercepted?=?true;??

????????????}??

????????????//?檢查cancel事件??

????????????final?boolean?canceled?=?resetCancelNextUpFlag(this)??

????????????????????||?actionMasked?==?MotionEvent.ACTION_CANCEL;??

????????????//?如果有第二個手指touch，更新touch目標列表。touch目標列表是一個View數組??

????????????final?boolean?split?=?(mGroupFlags?&?FLAG_SPLIT_MOTION_EVENTS)?!=?0;??

????????????TouchTarget?newTouchTarget?=?null;??

????????????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);??

????????????????????????//?找到一個能接受Event的子View，再對子View的View樹進行遍歷??

????????????????????????final?View[]?children?=?mChildren;??

????????????????????????final?boolean?customOrder?=?isChildrenDrawingOrderEnabled();??

????????????????????????//判斷每個子View是否是TouchTarget，若是則添加到TouchTarget鏈表中??

????????????????????????for?(int?i?=?childrenCount?-?1;?i?>=?0;?i--)?{??

????????????????????????????final?int?childIndex?=?customOrder????

????????????????????????????????????getChildDrawingOrder(childrenCount,?i)?:?i;??

????????????????????????????final?View?child?=?children[childIndex];??

????????????????????????????if?(!canViewReceivePointerEvents(child)??

????????????????????????????????????||?!isTransformedTouchPointInView(x,?y,?child,?null))?{??

????????????????????????????????continue;??

????????????????????????????}??

????????????????????????????newTouchTarget?=?getTouchTarget(child);??

????????????????????????????if?(newTouchTarget?!=?null)?{??

????????????????????????????????//?若子View處于touch目標中，同時已經接收了touch事件，則為器增加新的touch點??

????????????????????????????????newTouchTarget.pointerIdBits?|=?idBitsToAssign;??

????????????????????????????????break;??

????????????????????????????}??

????????????????????????????resetCancelNextUpFlag(child);??

????????????????????????????//把MotionEvent的點坐標轉換到子View的坐標系中，為ViewGroup創建一個新TouchTarget，TouchTarget包含了子View??

????????????????????????????if?(dispatchTransformedTouchEvent(ev,?false,?child,?idBitsToAssign))?{??

????????????????????????????????//?Child?wants?to?receive?touch?within?its?bounds.??

????????????????????????????????mLastTouchDownTime?=?ev.getDownTime();??

????????????????????????????????mLastTouchDownIndex?=?childIndex;??

????????????????????????????????mLastTouchDownX?=?ev.getX();??

????????????????????????????????mLastTouchDownY?=?ev.getY();??

????????????????????????????????newTouchTarget?=?addTouchTarget(child,?idBitsToAssign);??

????????????????????????????????alreadyDispatchedToNewTouchTarget?=?true;??

????????????????????????????????break;??

????????????????????????????}??

????????????????????????}??

????????????????????}??

????????????????????if?(newTouchTarget?==?null?&&?mFirstTouchTarget?!=?null)?{??

????????????????????????//?沒有發現接收event的子View，把Touch點賦給最早添加到TouchTarget鏈中的對象??

????????????????????????newTouchTarget?=?mFirstTouchTarget;??

????????????????????????while?(newTouchTarget.next?!=?null)?{??

????????????????????????????newTouchTarget?=?newTouchTarget.next;??

????????????????????????}??

????????????????????????newTouchTarget.pointerIdBits?|=?idBitsToAssign;??

????????????????????}??

????????????????}??

????????????}??

????????????//?傳遞給touch目標??

????????????if?(mFirstTouchTarget?==?null)?{??

????????????????//?若沒有Touch目標，則把自己當成一個View，調用??

????????????????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;??

????????????????while?(target?!=?null)?{??

????????????????????final?TouchTarget?next?=?target.next;??

????????????????????//若已被處理，則忽略。??

????????????????????if?(alreadyDispatchedToNewTouchTarget?&&?target?==?newTouchTarget)?{??

????????????????????????handled?=?true;??

????????????????????}?else?{??

????????????????????????final?boolean?cancelChild?=?resetCancelNextUpFlag(target.child)??

????????????????????????????????||?intercepted;??

????????????????????????//傳遞給子View處理??

????????????????????????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;??

????????????????}??

????????????}??

????????????//?若在觸摸點發生了up或cancel，則更新TouchTarget鏈表??

????????????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;??

????}??

ViewGroup中將TouchEvent傳遞給子View的函數為dispatchTransformedTouchEvent()，源代碼如下：

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?

[java]?view plaincopy

/**?

????*?Transforms?a?motion?event?into?the?coordinate?space?of?a?particular?child?view,?

????*?filters?out?irrelevant?pointer?ids,?and?overrides?its?action?if?necessary.?

????*?If?child?is?null,?assumes?the?MotionEvent?will?be?sent?to?this?ViewGroup?instead.?

????*/??

???private?boolean?dispatchTransformedTouchEvent(MotionEvent?event,?boolean?cancel,??

???????????View?child,?int?desiredPointerIdBits)?{??

???????final?boolean?handled;??

???????//?Canceling?motions?is?a?special?case.?We?don't?need?to?perform?any?transformations??

???????//?or?filtering.?The?important?part?is?the?action,?not?the?contents.??

???????//?cancel動作是個特列，無需坐標轉換或過濾。??

???????final?int?oldAction?=?event.getAction();??

???????if?(cancel?||?oldAction?==?MotionEvent.ACTION_CANCEL)?{??

???????????event.setAction(MotionEvent.ACTION_CANCEL);??

???????????if?(child?==?null)?{??

???????????????handled?=?super.dispatchTouchEvent(event);??

???????????}?else?{??

???????????????handled?=?child.dispatchTouchEvent(event);??

???????????}??

???????????event.setAction(oldAction);??

???????????return?handled;??

???????}??

???????//?計算將被傳遞的點的數量。??

???????final?int?oldPointerIdBits?=?event.getPointerIdBits();??

???????final?int?newPointerIdBits?=?oldPointerIdBits?&?desiredPointerIdBits;??

??

???????//?Motion事件沒有對應點，則丟棄這個Motion??

???????if?(newPointerIdBits?==?0)?{??

???????????return?false;??

???????}??

??

???????/*若點的數量一致則無需進行不相關的點坐標轉換，調用子View的dispatchTouchEvent*/??

???????//?If?the?number?of?pointers?is?the?same?and?we?don't?need?to?perform?any?fancy??

???????//?irreversible?transformations,?then?we?can?reuse?the?motion?event?for?this??

???????//?dispatch?as?long?as?we?are?careful?to?revert?any?changes?we?make.??

???????//?Otherwise?we?need?to?make?a?copy.??

???????/*該變量用于保存坐標轉換后的MoetionEvent*/??

???????final?MotionEvent?transformedEvent;??

???????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;??????

???????????????????/*直接對MotionEvent進行坐標變換，將MotionEvent傳遞下去*/??

???????????????????event.offsetLocation(offsetX,?offsetY);??

???????????????????handled?=?child.dispatchTouchEvent(event);??

???????????????????/*回復MotionEvent*/??

???????????????????event.offsetLocation(-offsetX,?-offsetY);??

???????????????}??

???????????????return?handled;??

???????????}??

???????????transformedEvent?=?MotionEvent.obtain(event);??

???????}?else?{??

???????????transformedEvent?=?event.split(newPointerIdBits);??

???????}??

???????//?Perform?any?necessary?transformations?and?dispatch.??

???????if?(child?==?null)?{??????

???????????/*調用父類即View的dispatchTouchEvent方法，該方法會調用onTouchEvent*/??

???????????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());??

???????????}??

???????????/*傳遞給子View處理*/??

???????????handled?=?child.dispatchTouchEvent(transformedEvent);??

???????}??

???????//?Done.??

???????transformedEvent.recycle();??

???????return?handled;??

???}??

View對象的dispatchTouchEvent代碼如下：

?

?

[java]?view plaincopy

/**?

???*?Pass?the?touch?screen?motion?event?down?to?the?target?view,?or?this?

???*?view?if?it?is?the?target.?

???*?

???*?@param?event?The?motion?event?to?be?dispatched.?

???*?@return?True?if?the?event?was?handled?by?the?view,?false?otherwise.?

???*/??

??public?boolean?dispatchTouchEvent(MotionEvent?event)?{??

??????if?(mInputEventConsistencyVerifier?!=?null)?{??

??????????mInputEventConsistencyVerifier.onTouchEvent(event,?0);??

??????}??

??????if?(onFilterTouchEventForSecurity(event))?{??

??????????//noinspection?SimplifiableIfStatement??

??????????ListenerInfo?li?=?mListenerInfo;??

??????????/*先調用listener接口*/??

??????????if?(li?!=?null?&&?li.mOnTouchListener?!=?null?&&?(mViewFlags?&?ENABLED_MASK)?==?ENABLED??

??????????????????&&?li.mOnTouchListener.onTouch(this,?event))?{??

??????????????return?true;??

??????????}??

?????????/*若MotionEvent未被消耗，則調用View的onTouchEvent?*?

??????????*?ViewGroup中沒有定義onTouchEvent，故做后調用View中的onTouchEvent*/??

??????????if?(onTouchEvent(event))?{??

??????????????return?true;??

??????????}??

??????}??

??????if?(mInputEventConsistencyVerifier?!=?null)?{??

??????????mInputEventConsistencyVerifier.onUnhandledEvent(event,?0);??

??????}??

??????return?false;??

??}??

?

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小結：

onInterceptTouchEvent:

onInterceptTouchEvent是在ViewGroup里面定義的，被ViewGroup.dispatchTouchEvent()調用，用于攔截所有的touch事件。默認返回false，表示不攔截touch事件，ViewGroup.dispatchTouchEvent()會調用子View的dispatchTouchEvent,將touch事件傳遞到子View中。若子View的dispatchTouchEvent?返回false，則ViewGroup的onTouchEvent會被調用；若子View的dispatchTouchEvent?返回true，表示消耗了手勢事件，ViewGroup的onTouchEvent則不會被調用。若ViewGroup.onInterceptTouchEvent()返回true，表示Touch事件被攔截，ViewGroup. dispatchTransformedTouchEvent()函數將被調用，該函數會調用super.dispatchTouchEvent(event)，即View的dispatchEvent()，該函數首先會調用View.OnTouchListener.onTouch().若listener未消耗Touch事件，則會調用View.onTouchEvent(). ?

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onTouchEvent:

view中定義的方法onTouchEvent默認返回true,表示消耗了一個touch事件，ViewGroup中定義的onTouchEvent默認返回false，表示不處理Touch手勢事件。手勢事件類型包括ACTION_DOWN,ACTION_MOVE,ACTION_UP,ACTION_CANCEL等事件。

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本節及后續都是參考了一篇國外講義，下載地址：http://download.csdn.net/detail/bigconvience/7376431

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轉載于:https://www.cnblogs.com/Free-Thinker/p/5501000.html

總結

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