Android View 觸摸屏事件派發機制和源碼分析

分類：編程 時間:2017-02-15

android View 觸摸屏事件派發機制和源碼分析

最近參考Android systemUI 的源碼其中涉及到很多事件派發和處理相關的問題.早期感覺很復雜,後面有時間了通過結合log來分析漸漸有一定的理解.現在參考網絡上面的文章自己也將這一方面的源碼分析一下,同時寫下來,以便然後回憶和加深理解.(基於mtk 的Android 5.1 系統)


Android 的觸摸事件都是從dispatchTouchEvent()開始的,View 和ViewGroup 都是一樣的.暫時只分析View,不分析ViewGroup.

1.View 的dispatchTouchEvent()開始

其實View的dispatchTouchEvent也是有父布局(某個ViewGroup,可以理解為LinerLayout)調用的.直接上源碼.
在判斷是ACTION_DOWN之前dispatchTouchEvent 做了處理手勢相關的工作(mInputEventConsistencyVerifier),這個具體還沒有研究,以後再研究,在筆記的後面有一個"Android的用戶輸入處理"可以參考.目前只是分析我們需要關註的重點. 
  1. public boolean dispatchTouchEvent(MotionEvent event) {
  2. 	// If the event should be handled by accessibility focus first.
  3. 	if (event.isTargetAccessibilityFocus()) {
  4. 		// We don't have focus or no virtual descendant has it, do not handle the event.
  5. 		if (!isAccessibilityFocusedViewOrHost()) {
  6. 			return false;
  7. 		}
  8. 		// We have focus and got the event, then use normal event dispatch.
  9. 		event.setTargetAccessibilityFocus(false);
  10. 	}
  12. 	boolean result = false;
  14. 	if (mInputEventConsistencyVerifier != null) {
  15. 		mInputEventConsistencyVerifier.onTouchEvent(event, 0);
  16. 	}
  18. 	if (DBG_MOTION || DEBUG_DEFAULT) {
  19. 		if (event.getAction() == MotionEvent.ACTION_DOWN) {
  20. 			Xlog.i(VIEW_LOG_TAG, "Touch down dispatch to " + this + ", event = " + event);
  21. 		} else if (event.getAction() == MotionEvent.ACTION_UP) {
  22. 			Xlog.i(VIEW_LOG_TAG, "Touch up dispatch to " + this + ", event = " + event);
  23. 		}
  24. 	}
  26. 	if (DBG_MOTION) {
  27. 		Xlog.d(VIEW_LOG_TAG, "(View)dispatchTouchEvent: event = " + event + ",this = " + this);
  28. 	}
  30. 	final int actionMasked = event.getActionMasked();
  31. 	if (actionMasked == MotionEvent.ACTION_DOWN) {
  32. 		// Defensive cleanup for new gesture
  33. 		stopNestedScroll();
  34. 	}
  36. 	if (onFilterTouchEventForSecurity(event)) {//判斷當前View 沒有被遮蔽
  37. 		//noinspection SimplifiableIfStatement
  38. 		ListenerInfo li = mListenerInfo;
  39. 		if (li != null && li.mOnTouchListener != null
  40. 				&& (mViewFlags & ENABLED_MASK) == ENABLED
  41. 				&& li.mOnTouchListener.onTouch(this, event)) {//1.設置touchListener,2.是enable狀態,3.touchListener的onTouch返回true
  42. 			/// M : add log to help debugging
  43. 			if (DBG_TOUCH) {
  44. 				Xlog.d(VIEW_LOG_TAG, "handle Touch event by listerner, listener = " + li
  45. 						+ ", event = " + event + ", this = " + this);
  46. 			}
  47. 			result = true;
  48. 		}
  50. 		if (!result && onTouchEvent(event)) {//touchListener的onTouch沒有返回false,或者沒有設置clickListener/longClickListener,而且onTouchEvent返回true.而且onTouchEvent返回什麽dispatchTouchEvent也會返回什麽
  51. 			/// M : add log to help debugging
  52. 			if (DBG_TOUCH) {
  53. 				Xlog.d(VIEW_LOG_TAG, "handle Touch event by onTouchEvent, event = "
  54. 					+ event + ", this = " + this);
  55. 			}
  56. 			result = true;
  57. 		}
  58. 	}
  60. 	/// M : add log to help debugging
  61. 	if (!result && DBG_TOUCH) {
  62. 		Xlog.d(VIEW_LOG_TAG, "Do not handle Touch event, event = "
  63. 		+ event + ", this = " + this);
  64. 	}
  66. 	if (!result && mInputEventConsistencyVerifier != null) {
  67. 		mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
  68. 	}
  70. 	// Clean up after nested scrolls if this is the end of a gesture;
  71. 	// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
  72. 	// of the gesture.
  73. 	if (actionMasked == MotionEvent.ACTION_UP ||
  74. 			actionMasked == MotionEvent.ACTION_CANCEL ||
  75. 			(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
  76. 		stopNestedScroll();
  77. 	}
  79. 	return result;
  80. }
在onFilterTouchEventForSecurity裏面看註釋就知道是判斷當前的View 有沒有被遮蔽.我們考慮的是沒有被遮蔽的情況,了就是onFilterTouchEventForSecurity返回true. dispatchTouchEvent 在39行有一個if判斷,這個判斷依次做了3個小判斷. if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) 第一步:li != null && li.mOnTouchListener != null,這個ListenerInfo 是不是為null並且mListenerInfo的mOnTouchListener  是不是為null.在View 的源碼裏面查找mListenerInfo就會找到是在getListenerInfo裏面調用的,接著會發現是在setOnClickListener裏面調用的.顯然也就是我們判斷我們也沒有給這個View 控件設置View.OnClickListener事件.如果有就已經第2部分的判斷 
  1. ListenerInfo getListenerInfo() {
  2. 	if (mListenerInfo != null) {
  3. 		return mListenerInfo;
  4. 	}
  5. 	mListenerInfo = new ListenerInfo();
  6. 	return mListenerInfo;
  7. }
  9. public void setOnClickListener(OnClickListener l) {
  10. 	if (!isClickable()) {
  11. 		setClickable(true);
  12. 	}
  13.  
    
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