Android ViewGroup 觸摸屏事件派發機制和源碼分析

分類：編程 時間:2017-02-15

android ViewGroup 觸摸屏事件派發機制和源碼分析

Android 中不管是View 還是ViewGoup,觸摸事件來的時候都是從dispatchTouchEvent開始的.其中dispatchTouchEvent()是View.Java 的方法,ViewGroup 只是重寫了這個方法. 看ViewGroup的dispatchTouchEvent() 之前最好先看View的dispatchTouchEvent().View 的邏輯簡單些,而且ViewGroup的dispatchTouchEvent()最終也會調用View的dispatchTouchEvent(). 以下分析基於Android L.
 我們現在從ViewGroup的dispatchTouchEvent()開始分析.相關代碼如下: 
  1. @Override
  2. public boolean dispatchTouchEvent(MotionEvent ev) {
  3. 	if (mInputEventConsistencyVerifier != null) {
  4. 		mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
  5. 	}
  7. 	// If the event targets the accessibility focused view and this is it, start
  8. 	// normal event dispatch. Maybe a descendant is what will handle the click.
  9. 	if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
  10. 		ev.setTargetAccessibilityFocus(false);
  11. 	}
  13. 	if (DBG_MOTION || DBG_TOUCH) {
  14. 		Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent 1: ev = " + ev + ",mFirstTouchTarget = "
  15. 				+ mFirstTouchTarget + ",this = " + this);
  16. 	}
  18. 	boolean handled = false;
  19. 	if (onFilterTouchEventForSecurity(ev)) {//調用View.java判斷當前View 沒有被遮蔽
  20. 		final int action = ev.getAction();
  21. 		final int actionMasked = action & MotionEvent.ACTION_MASK;
  23. 		// Handle an initial down.
  24. 		if (actionMasked == MotionEvent.ACTION_DOWN) {
  25. 			// Throw away all previous state when starting a new touch gesture.
  26. 			// The framework may have dropped the up or cancel event for the previous gesture
  27. 			// due to an app switch, ANR, or some other state change.
  28. 			cancelAndClearTouchTargets(ev);
  29. 			resetTouchState();//mFirstTouchTarget設置為null;mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
  30. 		}
  32. 		// Check for interception.
  33. 		final boolean intercepted;
  34. 		if (actionMasked == MotionEvent.ACTION_DOWN
  35. 				|| mFirstTouchTarget != null) {
  36. 			final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;//true:不攔截;false:攔截
  37. 			if (!disallowIntercept) {//攔截
  38. 				intercepted = onInterceptTouchEvent(ev);// 默認返回false
  39. 				/// M : add log to help debugging
  40. 				if (intercepted == true && DBG_TOUCH) {
  41. 					Xlog.d(TAG, "Touch event was intercepted event = " + ev
  42. 							+ ",this = " + this);
  43. 				}
  44. 				ev.setAction(action); // restore action in case it was changed
  45. 			} else {//不攔截
  46. 				intercepted = false;
  47. 			}
  48. 		} else {
  49. 			// There are no touch targets and this action is not an initial down
  50. 			// so this view group continues to intercept touches.
  51. 			intercepted = true;
  52. 		}
  54. 		// If intercepted, start normal event dispatch. Also if there is already
  55. 		// a view that is handling the gesture, do normal event dispatch.
  56. 		if (intercepted || mFirstTouchTarget != null) {
  57. 			ev.setTargetAccessibilityFocus(false);
  58. 		}
  60. 		// Check for cancelation.
  61. 		final boolean canceled = resetCancelNextUpFlag(this)
  62. 				|| actionMasked == MotionEvent.ACTION_CANCEL;//是否cancle事件
  64. 		// update list of touch targets for pointer down, if needed.
  65. 		final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;//默認true,用於判斷分發事件,作用是判斷可以把事件分發到多個子View.
  66. 		if (DBG_MOTION) {
  67. 			Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent 2: actionMasked = " + actionMasked
  68. 					+ ",intercepted = " + intercepted + ",canceled = " + canceled + ",split = "
  69. 					+ split + ",mChildrenCount = " + mChildrenCount + ",mFirstTouchTarget = "
  70. 					+ mFirstTouchTarget + ",this = " + this);
  71. 		}
  73. 		TouchTarget newTouchTarget = null;
  74. 		boolean alreadyDispatchedToNewTouchTarget = false;
  75. 		if (!canceled && !intercepted) {//沒有被攔截
  77. 			// If the event is targeting accessiiblity focus we give it to the
  78. 			// view that has accessibility focus and if it does not handle it
  79. 			// we clear the flag and dispatch the event to all children as usual.
  80. 			// We are looking up the accessibility focused host to avoid keeping
  81. 			// state since these events are very rare.
  82. 			View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
  83. 					? findChildWithAccessibilityFocus() : null;
  85. 			if (actionMasked == MotionEvent.ACTION_DOWN
  86. 					|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
  87. 					|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
  88. 				final int actionIndex = ev.getActionIndex(); // always 0 for down
  89. 				final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
  90. 						: TouchTarget.ALL_POINTER_IDS;
  92. 				// Clean up earlier touch targets for this pointer id in case they
  93. 				// have become out of sync.
  94. 				removePointersFromTouchTargets(idBitsToAssign);
  96. 				final int childrenCount = mChildrenCount;
  97. 				if (newTouchTarget == null && childrenCount != 0) {
  98. 					final float
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