View 的事件分发机制
2019-06-01 本文已影响0人
大盗海洲
事件分发1.jpg
public class Activity extends ContextThemeWrapper
implements LayoutInflater.Factory2,
Window.Callback, KeyEvent.Callback,
OnCreateContextMenuListener, ComponentCallbacks2,
Window.OnWindowDismissedCallback, WindowControllerCallback,
AutofillManager.AutofillClient {
/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*返回true，事件就被消费了
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
//事件若没有被消费，调用activity#onTouchEvent
return onTouchEvent(ev);
}
}
触摸屏幕，事件传递到activity ，再由activity#dispatchTouchEvent 分发下去，getWindow 是获取Window，而window是抽象类，具体实现类为PhoneWindow，事件走到PhoneWindow#superDispatchTouchEvent
public class PhoneWindow extends Window implements MenuBuilder.Callback {
// This is the top-level view of the window, containing the window decor.
//这是窗口的顶层视图，包含窗口装饰。
private DecorView mDecor;
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
}
事件传递到DecorView，DecorView为Activity的RootView（DecorView是当前界面的底层容器，就是setContentView所设置View的父容器）,是一个FrameLayout容器，即事件传递到ViewGrop#dispatchTouchEvent
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
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.
//down时，都清除touch上的标记和重置touch状态
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
//是否为down事件或事件是否被子View消费掉
//ViewGroup的点击事件被子View消费，那mFirstTouchTarget就指向该子view
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//一般子类调用requestDisallowInterceptTouchEvent 返回true，请求父类不拦截事件
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);//默认false，及ViewGroup默认不拦截事件
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;
}
}
}
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
if (!canceled && !intercepted) {//事件没有取消，也没有拦截事件
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 = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//倒序遍历子View，从外往里层View开始遍历
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;
}
//判断View 是否能接受事件
//1.View是Visibility ；2 .View 当前没有执行动画 ；3.在View 点击范围类
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;
//遍历到事件被哪个具体的View消费后，跳出遍历
break;
}
resetCancelNextUpFlag(child);
//事件分发给子View
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();
//如果子View消耗掉了事件，那么mFirstTouchTarget就会指向子View
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();
}
}
}
/**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
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) {
//ViewGrop 没有子View ，则事件将由父类dispatchTouchEvent 来传递下去
handled = super.dispatchTouchEvent(event);
} else {
//若有子View，事件将由子View的dispatchTouchEvent传递下去
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
}
小结：整一个if(!canceled && !intercepted){ ... }代码块所做的工作就是对ACTION_DOWN事件的特殊处理。因为ACTION_DOWN事件是一个事件序列的开始，所以我们要先找到能够处理这个事件序列的一个子View，如果一个子View能够消耗事件，那么mFirstTouchTarget会指向子View，如果所有的子View都不能消耗事件，那么mFirstTouchTarget将为null
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {//没有子View消费事件，事件传递给ViewGroup 自己的dispatchTouchEvent
// 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;
//这里就是区分了ACTION_DOWN事件和别的事件，因为在第3.2点
//的分析我们知道，如果子View消耗了ACTION_DOWN事件，那么 //alreadyDispatchedToNewTouchTarget和newTouchTarget已经有值了，所以就 //直接置handled为true并返回；
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {//不是down事件，即move、up
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//把事件分发给子View
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;
}
}
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
...
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
这段代码实现的功能是，如果ViewGroup中途拦截了事件，即intercepted为true。那么就会将触摸事件队列"清空"。这样就会使后续的触摸事件直接被ViewGroup默认拦截。
知识点：如果父View中途拦截了子View的触摸事件流，那么事件流中的后续事件将都被父View拦截，并且不能取消拦截。
View
public class View implements Drawable.Callback, KeyEvent.Callback,
AccessibilityEventSource {
public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
//mOnTouchListener 执行时机优先于onTouchEvent
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
}
public class View implements Drawable.Callback, KeyEvent.Callback,
AccessibilityEventSource {
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
//判断一个View是否能消费事件，clickable是否为true ，enabled 是否为true
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
//不管View 能否点击，它任然消费点击事件，只是用户收不到反馈
return clickable;
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
····
switch (action) {
case MotionEvent.ACTION_UP:
····
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
····
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
//onTouch>onTouchEvent>onClick
//onTouchListenter>onTouchEvent>onClickListener
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}
}
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