事件传递机制分析
来源：互联网 发布：柯蒂斯网络函授 编辑：程序博客网 时间：2024/06/06 18:56
为什么要有事件传递:
- 我们知道View是树形结构,当Touch事件(TouchEvent)产生时,可以有多个View去响应,那么为了解决到底哪个View消费这个Touch事件,就出现了事件传递机制.
- View结构图如下:
处理事件传递相关方法:
boolean dispatchTouchEvent(MotionEvent ev)用来进行事件的分发.如果事件能够传递到当前View,该方法一定会调用,返回值受当前View的onTouchEvent和下级View的dispatchTouchEvent()影响,表示是否消费当前事件.
boolean onInterceptTouchEvent(MotionEvent ev)在dispatchTouchEvent()内部调用,用来判是否拦截某个事件,返回结果表示是否拦截当前事件.
boolean onTouchEvent(MotionEvent ev)在dispatchTouchEvent()中调用,用来处理点击事件,返回结果受当前事件是否消费.
上述三个方法可以用一段伪代码来表示其关系:
public boolean dispatchTouchEvent(MotionEvent ev){ boolean consume=false; if(onInterceptTouchEvent(ev)){ consume=onTouchEvent(ev); }else{ consume= child.dispatchTouchEvent(ev); } return consume; }- 上述三个方法在Activity,ViewGroup,View中的存在关系:
事件传递消费的顺序:
当一个事件触发时，事件的流程：
Activity->PhoneWindow->DecorView->ViewGroup->...->View｀若最上层的View也没消费事件,事件则原路返回给Activity:
View->...->ViewGroup->DecorView->PhoneWindow->Activity
事件传递源码分析:
- 点击事件(MotionEvent)首先会传递给当前Activity,当前Activity的dispatchTouchEvent()会进行事件派发,具体工作由Activity内部的window完成,而Window是抽象的,Window的superDispatchTouchEvent()也是抽象,就有Window的唯一子类PhoneWindow处理事件.
- 我们首先分析Activity的dispatchTouchEvent():显然,首先事件交给Window进行分发,若返回true,整个事件结束,返回false表示没有View处理,那么Activity的OnTouchEvent()会被调用.
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }- 接着看看PhoneWindow是如果处理事件的: PhoneWindow直接将事件传递给了DecorView:
@Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }````* 而DecorView是FrameLayout的子类,也就将事件传递给了RootView:<div class="se-preview-section-delimiter"></div>public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event);}--------------<div class="se-preview-section-delimiter"></div>### ViewGroup* 首先ViewGroup对点击事件的分发过程,主要实现在dispatchTouchEvent():下面这段代码主要判断ViewGroup是否要去拦截事件:<div class="se-preview-section-delimiter"></div>// Check for interception.
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;
}
* ViewGroup会在两种情况下判断是否要拦截当前事件:事件类型类为ACTION_DOWN或者mFirstTouchTarget!=null,而mFirstTouchTarget的值取决于子View是否消费事件,如果子View不消费事件则mFirstTouchTarget!=null就不成立了.那么ACTION_MOVE或者ACTION_UP时,onInterceptTouchEvent()就不会调用了.* 当然还有一种特殊情况,就是FLAG_DISALLOW_INTERCEPT标记,这个子View通过requestDisallowInterceptTouchEvent()来设置,一旦设置ViewGroup将无法拦截除ACTION_DOWN以外的其他事件,因为在ACTION_DOWN时会重置FLAG_DISALLOW_INTERCEPT这个标记的值,因此当ACTION_DOWN时,ViewGroup总会调用onInterceptTouchEvent()来询问是否拦截事件.* 下面这段代码会在ACTION_DOWN时重置FLAG标记的值:ViewGroup决定拦截后,那么后续的点击事件默认交给他处理,并不调用onInterceptTouchEvent().<div class="se-preview-section-delimiter"></div> // 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(); }----------* 接着看ViewGroup不拦截事件情况:<div class="se-preview-section-delimiter"></div> if (!canceled && !intercepted) { 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<View> preorderedList = 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; } 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; } //.... } * 首先是遍历ViewGroup的所有子元素,判断子元素能否接受到点击事件,能否接受点击事件由两点衡量:子元素是否在播放动画和点击事件的坐标是否落在子元素的区域内.可以看到dispatchTransformTouchEvent()实际上是调用子元素的dispatchTouchEvent():<div class="se-preview-section-delimiter"></div>if (child == null) { handled = super.dispatchTouchEvent(event); } else { handled = child.dispatchTouchEvent(event); }* 如果子元素dispatchTouchEvent()返回true,则mFirstTouchTarget就是会被赋值跳出循环:<div class="se-preview-section-delimiter"></div>newTouchTarget = addTouchTarget(child, idBitsToAssign);alreadyDispatchedToNewTouchTarget = true;break;* 显然,mFirstTouchTarget的赋值是在addTouchTarget()内部完成的,从方法内部可以看出TouchTarget其实是一种单链表结构,mFirstTouchTarget是否赋值将直接影响ViewGroup对时间的拦截策略.<div class="se-preview-section-delimiter"></div>private TouchTarget addTouchTarget(View child, int pointerIdBits) { TouchTarget target = TouchTarget.obtain(child, pointerIdBits); target.next = mFirstTouchTarget; mFirstTouchTarget = target; return target;}* 如果子View都没有处理事件,ViewGroup将自己处理点击事件:dispatchTransformTouchEvent()在child为null时,调用View的dispatchTouchEvent(),这时事件就交给了View的dispatchTouchEvent()处理了.<div class="se-preview-section-delimiter"></div>// 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);}----------------* View的dispatchTouchEvent()对事件处理的代码如下:很显然,View对点击事件的处理,会先判断有没有设置OnTouchListener,若onTouch返回true,那么onTouchEvent()不会被调用,<div class="se-preview-section-delimiter"></div>public boolean dispatchTouchEvent(MotionEvent event) { //... 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; } } //.... return result;}* 接着分析View的onTouchEvent()方法:显然,即便View处于不可用状态下,事件也可以被消费掉.<div class="se-preview-section-delimiter"></div> if ((viewFlags & ENABLED_MASK) == DISABLED) { if (action == 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) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);}* 接着如果View设置有代理,那么会执行TouchDelegate的onTouchEvent():<div class="se-preview-section-delimiter"></div>if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } }* 接着看看OnTouchEvent()如何处理点击事件:只要有一个View的CLICKABLE和LONG_CLICKABLE为true,那么就会消费这个事件,当ACTION_UP事件发生时,会触发performClick(),如果设置了onClickLisetener,那么会调用onClick().<div class="se-preview-section-delimiter"></div> if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) { switch (action) { case MotionEvent.ACTION_UP: boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { //.... if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // This is a tap, so remove the longpress check removeLongPressCallback(); if (!focusTaken) { if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClick(); } } }“`
if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) { switch (action) { case MotionEvent.ACTION_UP: boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { //.... if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // This is a tap, so remove the longpress check removeLongPressCallback(); if (!focusTaken) { if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClick(); } } }- View处理相关事件的优先级如下:
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