編輯:關於Android編程
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }
當觸屏、按下Home鍵、back鍵、menu鍵等都會觸發onUserInteraction(),可以重寫這個方法處理一些用戶交互。可以看到Activity將事件交給Window來處理。如果Window不能消費事件Activity調用onTouchEvent()自行處理事件。PhoneWindow是Window的唯一實現類,接下來分析PhoneWindow分發事件過程。
public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }
mDecor是DecorView類的對象,DecorView繼承FrameLayout,PhoneWindow只是把事件交由頂級DecorView處理。由於DecorView繼承FrameLayout,FrameLayout繼承ViewGroup,所以,之後的事件分發過程與ViewGroup事件分發過程一樣。接下來Part2會介紹這部分。
事件首先傳遞給Activity,Activity將事件傳遞給Window(PhoneWindow是其實現類),Window把事件交給頂級DecorView處理,如果Window沒有消費這個事件則Activity調用oTouchEvent()自行處理事件。
事件傳遞順序:
只針對主要流程以及相應代碼進行分析,不會貼出完整代碼。ViewGroup的事件分發過程主要在dispatchTouchEvent()方法中。
首先,對MotionEvent做個簡單介紹。事件序列開始於ACTION_DOWN,終於ACTION_UP。對於單指操作有ACTION_DOWN、ACTION_MOVE、ACTION_UP等事件序列組成。多指操作由ACTION_DOWN、ACTION_POINTER_DOWN、ACTION_MOVE、ACTION_POINTER_UP、ACTION_UP事件序列組成。pointer可以理解為觸摸點。多指對應的pointerId不變,pointerIndex在事件序列中是變化的。
更多參考:http://www.jianshu.com/p/0c863bbde8eb
事件序列的起始動作是ACTION_DOWN,在新事件序列到達時要做一些狀態清除操作。
// Handle an initial down. 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. /**由於一些特殊原因丟失ACTION_UP或者ACTION_CANCEL, *導致事件序列結束時mFirstTouchTarget(TouchTarget鏈表)未被清空, * 新事件序列到達時,要先清空mFirstTouchTarget */ cancelAndClearTouchTargets(ev); //主要設置 mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT resetTouchState(); }
看看cancelAndClearTouchTargets()和resetTouchState()的具體實現。
/** * Cancels and clears all touch targets. */ private void cancelAndClearTouchTargets( MotionEvent event ) { if ( mFirstTouchTarget != null ) { boolean syntheticEvent = false; if ( event == null ) { final long now = SystemClock.uptimeMillis(); event = MotionEvent.obtain( now, now, MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0 ); event.setSource( InputDevice.SOURCE_TOUCHSCREEN ); syntheticEvent = true; } for ( TouchTarget target = mFirstTouchTarget; target != null; target = target.next ) { resetCancelNextUpFlag( target.child ); dispatchTransformedTouchEvent( event, true, target.child, target.pointerIdBits ); } clearTouchTargets(); if ( syntheticEvent ) { event.recycle(); } } }
dispatchTransformedTouchEvent()後面再分析,先來看clearTouchTargets()方法。
/** * Clears all touch targets. */ private void clearTouchTargets() { TouchTarget target = mFirstTouchTarget; if ( target != null ) { do { TouchTarget next = target.next; target.recycle(); target = next; } while ( target != null ); mFirstTouchTarget = null; } }
顯而易見,clearTouchTargets()對mFirstTouchTarget指向的鏈表進行了清空操作。
接下來看看resetTouchState()方法的實現:
private void resetTouchState() { clearTouchTargets(); resetCancelNextUpFlag(this); mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT; mNestedScrollAxes = SCROLL_AXIS_NONE; }
同樣對mFirstTouchTarget指向的鏈表進行了清空,更重要的是設置了~FLAG_DISALLOW_INTERCEPT標志位。引出一個結論,子View在ACTION_DOWN時調用ViewGroup的requestDisallowInterceptTouchEvent()方法是無效的。
接下來ViewGroup檢測是否要攔截事件:
/* Check for interception. */ final boolean intercepted; /* ACTION_DOWN或者mFirstTouchTarget!=null時檢測是否要攔截事件 */ if ( actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null ) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if ( !disallowIntercept ) { intercepted = onInterceptTouchEvent( ev ); /* restore action in case it was changed */ ev.setAction( action ); } 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; }
通過上面代碼,可以看出,ViewGroup在ACTON_DOWN或mFirstTouchTarget!=null條件時都會檢測是否需要攔截事件;在mFirstTouchTarget!=null的情況下,可以通過設置FLAG_DISALLOW_INTERCEPT或~FLAG_DISALLOW_INTERCEPT標記位來決定ViewGroup是否允許攔截ACTION_DOWN之後的事件,在允許攔截的情況下是否攔截還取決於onInterceptTouchEvent()的返回值。對於滑動沖突,方案一:使用onInterceptTouchEvent()攔截事件;方案二:使用onInterceptTouchEvent()和requestDisallowInterceptTouchEvent()一起攔截事件。個人覺得方案一更為簡單實用。
接下來ViewGroup會遍歷Children,尋找能消費事件的Child。實現代碼如下:
/* * Check for cancelation. * PFLAG_CANCEL_NEXT_UP_EVENT標記位文檔解釋是Indicates whether the view is temporarily detached */ 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; /* View detached或者event類型為ACTION_CANCEL或者未被攔截 */ if ( !canceled && !intercepted ) { /* * If the event is targeting accessiiblity focus we give it to the * view that has accessibility focus and if it does not handle it * we clear the flag and dispatch the event to all children as usual. * We are looking up the accessibility focused host to avoid keeping * state since these events are very rare. */ View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus() ? findChildWithAccessibilityFocus() : null; 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 */ /* 這裡處理多觸控情況,一個View如果有多指觸摸,用32位的int記錄不同Pointer */ 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 ArrayListpreorderedList = buildOrderedChildList(); final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); final View[] children = mChildren; for ( int i = childrenCount - 1; i >= 0; i-- ) { final int childIndex = customOrder ? getChildDrawingOrder( childrenCount, i ) : i; final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get( 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; } /* Child不可見並且無動畫直接跳過,或者Point不在child范圍內 */ if ( !canViewReceivePointerEvents( child ) || !isTransformedTouchPointInView( x, y, child, null ) ) { ev.setTargetAccessibilityFocus( false ); continue; } /* mFirstTouchTarget鏈表已經存在消費該事件的Child,用於多點觸控 */ newTouchTarget = getTouchTarget( child ); if ( newTouchTarget != null ) { /* * 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 ); /* 如果Child能消費事件,Child加入到mFirstTouchTarget鏈表 */ 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(); newTouchTarget = addTouchTarget( child, idBitsToAssign ); alreadyDispatchedToNewTouchTarget = true; 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; } } }
在ACTION_DOW或者ACTION_POINTER_DOWN時ViewGroup遍歷Children,尋找能夠消費事件的Child。Child不在TouchTarget鏈表中,addTouchTarget(child, idBitsToAssign);Child已經存在TouchTarget鏈表中,多指觸摸同一View情況,newTouchTarget.pointerIdBits |= idBitsToAssign。ViewGroup對於多指觸控不同View的解決方案是使用鏈表,View對於多指觸控的方案是使用32位int來記錄每個Pointer。
找到能夠消費事件序列的Child後,ACTION_DOWN或ACTION_POINTER_DOWN之後的事件,在ViewGroup不攔截的情況下,直接交由Child處理;一旦被攔截,在dispatchTransformedTouchEventChild()方法中eventAction會置為ACTION_CANCEL,並且Child會從TouchTarget鏈表中清除,因此接收不到後續事件序列,都將交給ViewGroup處理。實現代碼如下:
/* * Dispatch to touch targets. * Child不能消費事件序列,交由ViewGroup處理 */ if ( mFirstTouchTarget == null ) { /* No touch targets so treat this as an ordinary view. */ 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; /* 除去ACTION_DOWN或ACTION_POINTER_DOWN事件,因為在尋找過程中已經處理過 */ if ( alreadyDispatchedToNewTouchTarget && target == newTouchTarget ) { handled = true; } else { final boolean cancelChild = resetCancelNextUpFlag( target.child ) || intercepted; if ( dispatchTransformedTouchEvent( ev, cancelChild, target.child, target.pointerIdBits ) ) { handled = true; } /* PFLAG_CANCEL_NEXT_UP_EVENT重置或者ViewGroup攔截ACTION_DOWN或ACTION_POINTER_DOWN 之後的事件,清除相應TouchTarget */ if ( cancelChild ) { if ( predecessor == null ) { mFirstTouchTarget = next; } else { predecessor.next = next; } target.recycle(); target = next; continue; } } predecessor = target; target = next; } }
ViewGroup通過dispatchTransformedTouchEvent()方法將事件分發給Child。
/* Perform any necessary transformations and dispatch. */ if ( child == null ) { handled = super.dispatchTouchEvent( transformedEvent ); } else { /* 將event坐標轉換成Child坐標系內坐標 */ 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 ); }
未找到可消費事件的Child,ViewGroup自行處理事件序列;否則,將event坐標轉換成Child坐標系內坐標交由Child處理。
ACTION_UP觸發事件序列結束時清空TouchTarget,ACTION_PONITER_UP觸發時,清空相應pointer的target。
/* 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 ); }
ViewGroup事件分發的流程圖整理如下:
ViewGroup的事件分發過程就分析完了,接下來分析View的事件分發過程,相對ViewGroup來說相對簡單。
注意:View只處理了單指觸控的情況,未實現多指觸控,如果有需要可以自己實現。針對View的事件分發只涉及單指情況。View的事件分發過程同樣在dispatchTouchEvent()方法中,主要對這個方法進行分析即可。
View的事件分發過程同樣在dispatchTouchEvent()方法中,主要對這個方法進行分析即可。
final int actionMasked = event.getActionMasked(); if (actionMasked == MotionEvent.ACTION_DOWN) { // Defensive cleanup for new gesture stopNestedScroll(); }
上面代碼表示,ACTION_DOWN事件會使View停止滾動(如果View是能夠滾動的,比如ListView)。
接下來View就要開始處理事件了,代碼如下:
if (onFilterTouchEventForSecurity(event)) { //noinspection SimplifiableIfStatement ListenerInfo li = mListenerInfo; if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { result = true; } if (!result && onTouchEvent(event)) { result = true; } }
View狀態是ENABLE並且調用過setOnTouchListener()方法,事件是否能被OnTouchListener消費取決於onTouch()的返回值。未調用過setOnTouchListener()方法或者OnTouchListener未消費事件,由onTouchEvent()方法來處理事件,事件是否能被消費取決於onTouchEvent()的返回值。接下來看看onTouchEvent()具體實現。
if ( (viewFlags & ENABLED_MASK) == DISABLED ) { if ( event.getAction() == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0 ) { setPressed( false ); } /* * A disabled view that is clickable still consumes the touch * events, it just doesn't respond to them. */ return( ( (viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ); }
其實,View是CLICKABLE或者LONG_CLICKABLE時返回結果都為true(具體可查看源碼),也就是View能夠消費事件。上面的情況是View是DISABLED狀態時,會在ACTION_UP或者(mPrivateFlags & PFLAG_PRESSED) != 0設置mPrivateFlags &= ~PFLAG_PRESSED。長按以及點擊事件執行前都會先對這個標記位進行判斷。View處於DISABLED狀態可以消費事件,但是單擊和長按事件不會執行。
if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } }
這段代碼表示可以給View設置一個代理對象(別的View),使用代理對象的onTouchEvent()來處理事件。比如擴大View的接觸面積、幾個View同步處理事件都可以用到。
對於View的事件處理,主要分析對ACTION_DOWN和ACTION_UP進行分析。先來看對ACTION_DOWN事件的處理:
/* * For views inside a scrolling container, delay the pressed feedback for * a short period in case this is a scroll. */ if ( isInScrollingContainer ) { mPrivateFlags |= PFLAG_PREPRESSED; if ( mPendingCheckForTap == null ) { mPendingCheckForTap = new CheckForTap(); } mPendingCheckForTap.x = event.getX(); mPendingCheckForTap.y = event.getY(); postDelayed( mPendingCheckForTap, ViewConfiguration.getTapTimeout() ); } else { /* Not inside a scrolling container, so show the feedback right away */ setPressed( true, x, y ); checkForLongClick( 0 ); }
在滾動容器中的操作只是增加了個延時操作,本質還是和不在滾動容器中一樣的。來看看checkForLongClick()方法的實現:
private void checkForLongClick( int delayOffset ) { if ( (mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE ) { mHasPerformedLongPress = false; if ( mPendingCheckForLongPress == null ) { mPendingCheckForLongPress = new CheckForLongPress(); } mPendingCheckForLongPress.rememberWindowAttachCount(); postDelayed( mPendingCheckForLongPress, ViewConfiguration.getLongPressTimeout() - delayOffset ); } }
postDelayed()向Handler的消息隊列插入一個待處理的Runable對象,並且設置延時,這也是為什麼需要長按一段時間,長按操作才會執行。長按操作的具體實現都在CheckForLongPress裡了。
private final class CheckForLongPress implements Runnable { private int mOriginalWindowAttachCount; @Override public void run() { if ( isPressed() && (mParent != null) && mOriginalWindowAttachCount == mWindowAttachCount ) { if ( performLongClick() ) { mHasPerformedLongPress = true; } } } public void rememberWindowAttachCount() { mOriginalWindowAttachCount = mWindowAttachCount; } }
看到重點了,performLongClick()會執行setOnLongClickListener()方法設置的OnLongClickListener的onLongClick()方法。
最後來看看View對ACTION_UP事件的處理:
if ( !mHasPerformedLongPress ) { /* 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 ) ) { performClick(); } } }
如果mHasPerformedLongPress為false (可能OnLongClickListener為空或者onLongCkcik()方法返回false),移除隊列中的CheckForLongPress對象,然後如果OnClickListener不為空執行onClick()方法。
注意:給一個Button設置OnLongClickListener和OnClickListener,onLongClick()方法返回false。這種情況長按和點擊都會執行,驗證方法不能使用System.out.print()來進行輸出驗證,因為System.out是一個有緩存的輸出流,print()並不會立即輸出,使用println()才會立即輸出。
View的狀態是CLICKABLE或者LONG_CLICKABLE都能夠消費事件,如果是DISABLED狀態則不會觸發長按和點擊事件。單擊事件優先級最低,因為最後才會處理單擊事件。
至此,Android事件分發機制分析完畢。
上圖為代碼結構圖。現在我們看下具體的代碼。Send.javapackage cn.com.sms.send; import java.util.ArrayList; i
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