在 更简单的学习Android事件分发 中,使用日志、比喻、流程图相结合的方式,以更简单的方法去分析了Android的事件分发机制。本篇文章将采用分析源码的方式,更深入的解析Android的事件分发机制。
Android的触摸事件,是由windowManagerService进行采集,之后传递到Activiy进行处理。我们这里从Activity#dispatchTouchEvent方法开始解析
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }
上述代码中, onUserInteraction()
是一个空的实现,我们直接来看下
getWindow().superDispatchTouchEvent(ev)
方法。window是一个抽象的方法,不过系统给它提供了一个实现类PhoneWindow,我们这里看下它的 superDispatchTouchEvent(ev)
方法。
public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }
上述代码调用了DecorView类的 superDispatchTouchEvent
方法,继续跟进
public boolean superDispatchTouchEvent(MotionEvent event) { return super.dispatchTouchEvent(event); }
上述代码调用了父类的 dispatchTouchEvent
方法,DecorView的父类为FrameLayout,其直接继承了 ViewGroup#dispatchTouchEvent
方法。
ViewGroup#dispatchTouchEvent方法比较长,这里只截取部分进行分析
public boolean dispatchTouchEvent(MotionEvent ev) { ... // 在ACTION_DOWN事件时,初始化Touch标记 // 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. cancelAndClearTouchTargets(ev); resetTouchState(); } // Check for interception. final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { // 是否拦截的标志位,假如设置requestDisallowInterceptTouchEvent(true), // 则为true,不拦截事件 final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { // 默认返回false 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; } ... // 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; // 不是ACTION_CANCEL事件,并且不拦截事件 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) { // 获取触摸坐标 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<View> preorderedList = buildOrderedChildList(); final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); final View[] children = mChildren; // 遍历所有子View 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); ... resetCancelNextUpFlag(child); // 把事件(ACTION_DOWN、ACTION_POINTER_DOWN、ACTION_HOVER_MOVE)传递给子View处理 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; } ... } ... } ... } } } // 分发事件到目标View // Dispatch to touch targets. if (mFirstTouchTarget == null) { // 没有找到事件分发目标的情况,将会调用自己的onTouchEvent方法 // 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; // 这里找到了事件分发的目标 while (target != null) { final TouchTarget next = target.next; // ACTION_DOWN已经完成事件分发,并消费了事件,直接返回true if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; // 其余事件则需要传递给目标View进行处理 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; } } // 对ACTION_CANCEL事件进行处理 // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { // 重置Touch状态 resetTouchState(); } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } } ... return handled; } // 默认返回false public boolean onInterceptTouchEvent(MotionEvent ev) { return false; }
我们现在来看看传递事件的 dispatchTransformedTouchEvent
方法,同样我也只是截取了其中比较关键的部分
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled; ... final MotionEvent transformedEvent; // 对transformedEvent的一系列计算 ... if (child == null) { // 如果没有子View,则执行super.dispatchTouchEvent方法, // 调用自己的onTouchEvent方法 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()); } // 如果有子View,则调用子View#dispatchTouchEvent方法 handled = child.dispatchTouchEvent(transformedEvent); } // Done. transformedEvent.recycle(); return handled; }
ViewGroup中不拦截事件,调用子View#dispatchTouchEvent方法进行处理
public boolean dispatchTouchEvent(MotionEvent event) { ... if (onFilterTouchEventForSecurity(event)) { // 如果设置了OnTouchListener,使用onTouch对事件进行处理, // 并返回true,则不需要再执行onTouchEvent方法 //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; } } ... return result; }
这里继续看看View#onTouchEvent方法
public boolean onTouchEvent(MotionEvent event) { final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); ... if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) { switch (action) { case MotionEvent.ACTION_UP: ... // 移除长按 removeLongPressCallback(); ... // 检查单击 performClick(); ... break; case MotionEvent.ACTION_DOWN: ... // 检测是否为长按 checkForLongClick(0); ... break; .... } return true; } return false; }
上述代码,主要是检查View是否可以点击,如果可点击,则会返回true,同时也会执行可点击的事件。
四、小结
通过本文的源码解析,我们可以更深入的理解Android的事件分发。可以简单的推出一个流程 : Activity→PhoneWindow→DecorView→ViewGroup→View。如果在阅读过程中,有任何疑问与问题,欢迎与我联系。
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