view系列源码分析之事件分发 view系列源码分析之事件分发

继上一篇文章事件分发基础篇之结论篇之后，有人问我怎么得出的这个结论的，那所有的依据当然得依靠源码的支持，那我们从viewGroup的dispatchTouchEvent开始说起

@Override public boolean dispatchTouchEvent(MotionEvent ev) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(ev, 1); }// If the event targets the accessibility focused view and this is it, start // normal event dispatch. Maybe a descendant is what will handle the click. if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) { ev.setTargetAccessibilityFocus(false); }boolean handled = false; if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; // 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. （1）cancelAndClearTouchTargets(ev); resetTouchState(); }// Check for interception.（主要是onInterceptTouchEvent的）（2） final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { 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 { // There are no touch targets and this action is not an initial down // so this view group continues to intercept touches. intercepted = true; }// If intercepted, start normal event dispatch. Also if there is already // a view that is handling the gesture, do normal event dispatch. if (intercepted || mFirstTouchTarget != null) { ev.setTargetAccessibilityFocus(false); }// Check for cancelation. 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; （3）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 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 ArrayList 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); // 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; }if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; }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); 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; } } }// Dispatch to touch targets. 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; if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { 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; } }// 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); } }if (!handled && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1); } return handled; }

这是viewGroup分发的源码，挑重点的说
（1）首先在处理下一次的的down事件的时候，是清除mFirstTouchTargets的(就是寻找到view的标记，这个标记在down事件找到在move和up还回去找么，肯定不会，直接拿来用就行了)
（2）这里很关键,当mFirstTarget!=null或者是down事件时会调用拦截的，其实我们知道mFirstTarget就是down事件找到一个点击的最终的view,这里就是说当找到了move和up也会调用拦截方法，也就印证了结论每次都要询问拦截，当然final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; 这个最终标记是位运算&后是否有值，也就是我们子类设置的这个标志（一般在down里设置）
（3）这里是是一个down的for循环，down事件用来寻找mFirstTarget
那mFirstTouchTarget是哪里被赋值的呢，很明显在addTouchTarget方法中，要进入这个方法，必须down事件返回true

private TouchTarget addTouchTarget(View child, int pointerIdBits) { TouchTarget target = TouchTarget.obtain(child, pointerIdBits); target.next = mFirstTouchTarget; mFirstTouchTarget = target; return target; }

这里给mFirstTarget赋值了，当然在结束循环后，如果没有找到mFirstTarget,那就调用dispatchTransformedTouchEvent(ev, canceled, null,TouchTarget.ALL_POINTER_IDS);

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. 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; }

也就是自身的dispatchTouchEvent，如果找到了就会发一个子view的cancel事件
由此可以用伪代码来说下

if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); } else { intercepted = false; } } else { intercepted = true; }//查找合适的子view，注意只针对down事件 if(down事件&&!intercepted){ handled=某个child.dispatchTouchEvent(); if(handled){ mFirstTouchTarget赋值 }else{ //这里子view处理不了交给父view处理的原因 mFirstTouchTarget==null; }}if(mFirstTouchTarget==null){ handled=super.dispatchTouchEvent() }else{ if(intercepted){ mFirstTouchTarget发一个cancel事件 mFirstTouchTarget=null； }else{ return mFirstTouchTarget.dispatchTouchEvent(); }} return handled;

这里说下view的move和up事件由于已经有了mFirstTarget(down的时候返回了true),所以即使move和up返回了false，也不影响事件的执行，只影响到dispatchtouchevent，当子view的down事件返回false时，并不会对mFirstTarget赋值
当然了在view的dispatchTouchEvent里就简单很多了，返回的和ontouchlistener有关系，如果为空，就调用ontouchEvent，默认可以点击的返回true，不可点击的返回false。
【view系列源码分析之事件分发】此次事件分发也告一段落了，主要是viewGroup的dispatchTouchEvent
读懂，自然也懂了..