Android View事件分发机制 (一)
当一个点击事件发生时,事件的传递顺序是从Activity -> PhoneWindow -> DecorView(当前界面的容器,setContentView最终得到的布局就是添加到DecorView),然后事件就传递给setContentView这个布局设置的View树上。事件传递的入口是从Activity dispatchTouchEvent 开始处理。
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
//将事件传递到window上,然后再到DecorView
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
这里就不去追踪上面的代码的执行过程了,可以查看下PhoneWindow的superDispatchTouchEvent 方法。
接下来我们了解下Activity ViewGroup 和 View 这三者之间的事件分发处理的逻辑。接下来就引出了众所周知的三个核心方法
1、 public boolean dispatchTouchEvent(MotionEvent ev) {}
2、 public boolean onInterceptTouchEvent(MotionEvent ev) {}
3、 public boolean onTouchEvent(MotionEvent event) {}
Activity 和View 只有dispatchTouchEvent 和 onTouchEvent 方法而ViewGroup有这个三个方法。
接下来我们通过日志和操纵dispatchTouchEvent 、onInterceptTouchEvent、onTouchEvent 来观察下事件到底是如何传递的。
public class EventDeliverActivity extends Activity {
private static final String TAG = "EventDeliverActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_event_deliver);
/*
//情况四 案例
findViewById(R.id.view_1).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "onClick: view_1");
}
});
findViewById(R.id.view_1).setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
Log.d(TAG, "onLongClick: view_1");
return false;
}
});
findViewById(R.id.view_1).setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.d(TAG, "onTouch: view_1");
return false;
}
});
*/
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " dispatchTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " dispatchTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " dispatchTouchEvent: ACTION_UP");
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " onTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " onTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " onTouchEvent: ACTION_UP");
break;
}
return super.onTouchEvent(event);
}
}
public class ViewGroup_1 extends FrameLayout {
private static final String TAG = "ViewGroup-1";
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " dispatchTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " dispatchTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " dispatchTouchEvent: ACTION_UP");
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " onInterceptTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " onInterceptTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " onInterceptTouchEvent: ACTION_UP");
break;
}
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " onTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " onTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " onTouchEvent: ACTION_UP");
break;
}
return super.onTouchEvent(event);
}
}
public class View_1 extends TextView {
private static final String TAG = "View_1";
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " dispatchTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " dispatchTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " dispatchTouchEvent: ACTION_UP");
break;
}
return super.dispatchTouchEvent(event);
//return true;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG, " onTouchEvent: ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, " onTouchEvent: ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, " onTouchEvent: ACTION_UP");
break;
}
return super.onTouchEvent(event);
//return true;
}
}
为了节约篇幅删除了一些构造方法。下面我们通过控制三个核心方法,是否分发、是否中断、是否处理来观察事件的执行过程。
情况一 Activity -> ViewGroup_1 -> View_1 所有的事件方法都不做任何处理
事件传递顺序是:
DOWN事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: onInterceptTouchEvent: ACTION_DOWN
View_1: dispatchTouchEvent: ACTION_DOWN
View_1: onTouchEvent: ACTION_DOWN
ViewGroup-1: onTouchEvent: ACTION_DOWN
EventDeliverActivity: onTouchEvent: ACTION_DOWN
MOVE事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
EventDeliverActivity: onTouchEvent: ACTION_MOVE
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
EventDeliverActivity: onTouchEvent: ACTION_MOVE
UP事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_UP
EventDeliverActivity: onTouchEvent: ACTION_UP
综上得出结论: 事件传递的过程是 先dispatchTouchEvent
-> onInterceptTouchEvent
-> onTouchEvent
并且dispatchTouchEvent
和 onInterceptTouchEvent
在同一级调用就是说Activity
调用完了dispatchTouchEvent
,会调用DecorView
的 dispatchTouchEvent
和onInterceptTouchEvent
方法,接着调用ViewGroup-1的dispatchTouchEvent
和onInterceptTouchEvent
方法 ,然后调用View_1的dispatchTouchEvent
方法,接着在从onTouchEvent
依次往上开始回调父View的onTouchEvent
。
情况二 Activity -> ViewGroup_1 -> View_1 在View_1的dispatchTouchEvent 或者 onTouchEvent 返回true
对View_1 的 dispatchTouchEvent return true
一、对View_1 的 dispatchTouchEvent return true
DOWN事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: onInterceptTouchEvent: ACTION_DOWN
View_1: dispatchTouchEvent: ACTION_DOWN
MOVE事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: onInterceptTouchEvent: ACTION_MOVE
View_1: dispatchTouchEvent: ACTION_MOVE
UP事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_UP
ViewGroup-1: dispatchTouchEvent: ACTION_UP
ViewGroup-1: onInterceptTouchEvent: ACTION_UP
View_1: dispatchTouchEvent: ACTION_UP
二、对View_1 的 onTouchEvent return true
DOWN事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: onInterceptTouchEvent: ACTION_DOWN
View_1: dispatchTouchEvent: ACTION_DOWN
View_1: onTouchEvent: ACTION_DOWN
MOVE事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: onInterceptTouchEvent: ACTION_MOVE
View_1: dispatchTouchEvent: ACTION_MOVE
View_1: onTouchEvent: ACTION_MOVE
UP事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_UP
ViewGroup-1: dispatchTouchEvent: ACTION_UP
ViewGroup-1: onInterceptTouchEvent: ACTION_UP
View_1: dispatchTouchEvent: ACTION_UP
View_1: onTouchEvent: ACTION_UP
综上得出结论: dispatchTouchEvent
或者 onTouchEvent
返回true 将会直接导致事件被终止,如何终止? 如DOWN事件它会不继续往下传递,而是走MOVE和UP事件。调用顺序是Activity 的dispatchTouchEvent
DOWN事件 然后会调用DecorView
的 dispatchTouchEvent
和onInterceptTouchEvent
方法接着会调用ViewGroup_1的 dispatchTouchEvent
和onInterceptTouchEvent
方法的DOWN事件,然后调用View_1的dispatchTouchEvent
DOWN事件, 然后DOWN事件就终止了,继续MOVE和UP时间。对于ViewGroup_1 也是同样的道理这里就不举例了。
情况三 Activity -> ViewGroup_1 -> View_1 在ViewGroup_1的onInterceptTouchEvent 返回true
DOWN事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: onInterceptTouchEvent: ACTION_DOWN
ViewGroup-1: onTouchEvent: ACTION_DOWN
EventDeliverActivity: onTouchEvent: ACTION_DOWN
MOVE事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
EventDeliverActivity: onTouchEvent: ACTION_MOVE
UP事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_UP
EventDeliverActivity: onTouchEvent: ACTION_UP
综上得出结论,如果在ViewGroup_1的onInterceptTouchEvent
返回true 它会导致事件不在向下传,而是直接给它自己的onTouchEvent
处理,然后根据onTouchEvent
返回情况,在调用自己的父View的onTouchEvent
。 简单说就是改变了事件的传递方向。 好比一个球从十楼开始*落体,dispatchTouchEvent
向下走,onInterceptTouchEvent
是决定是否要反弹,onTouchEvent
是向上走。 现在在中间楼层的onInterceptTouchEvent
返回true, 那么球就从中间楼层开始反弹了,而不是一直掉到一楼才开始反弹向上走。
情况四 看看View_1 onTouch onClick 以及 onLongClick方法的调用时机
DOWN事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: dispatchTouchEvent: ACTION_DOWN
ViewGroup-1: onInterceptTouchEvent: ACTION_DOWN
View_1: dispatchTouchEvent: ACTION_DOWN
EventDeliverActivity: onTouch: view_1
View_1: onTouchEvent: ACTION_DOWN
MOVE事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: dispatchTouchEvent: ACTION_MOVE
ViewGroup-1: onInterceptTouchEvent: ACTION_MOVE
View_1: dispatchTouchEvent: ACTION_MOVE
EventDeliverActivity: onTouch: view_1
View_1: onTouchEvent: ACTION_MOVE
UP事件:
EventDeliverActivity: dispatchTouchEvent: ACTION_UP
ViewGroup-1: dispatchTouchEvent: ACTION_UP
ViewGroup-1: onInterceptTouchEvent: ACTION_UP
View_1: dispatchTouchEvent: ACTION_UP
EventDeliverActivity: onTouch: view_1
View_1: onTouchEvent: ACTION_UP
EventDeliverActivity: onClick: view_1
综上上面的打印日志分析得出, view_1的onClick
事件发生在UP事件以后响应,并且在View_1的onTouchEvent
中响应。view_1 的 onTouch
方法发生在 dispatchTouchEvent
和 onTouchEvent
之间。
结合源码查看验证,分别在View.java 的 public boolean dispatchTouchEvent(MotionEvent event) {}
方法中,可以看到先是调用 li.mOnTouchListener.onTouch(this, event)
方法, 如果返回true的话,就会得到result=true if (!result && onTouchEvent(event)) {}
就可以得出 onTouchEvent
不会被执行。如果返回false onTouchEvent
方法被执行,接着在ACTION_UP事件处理时,performClickInternal()
-> performClick()
调用
调用onClick方法在onTouchEvent
ACTION_DOWN 事件中 checkForLongClick(0, x, y);
触发longClick
事件。
public boolean dispatchTouchEvent(MotionEvent event) {
boolean result = false;
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
&& li.mOnTouchListener.onTouch(this, event)) {
//onTouch方法的返回值讲直接决定了onTouchEvent是否被调用,如果返回true 代表事件被消费处理
result = true;
}
// onTouchEvent 处理onClick和onLongClick事件
if (!result && onTouchEvent(event)) {
result = true;
}
}
return result;
}
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
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.
return clickable;
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// 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)) {
//处理点击事件
performClickInternal();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
if (!clickable) {
//检查是否是长按事件
checkForLongClick(0, x, y);
break;
}
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break;
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
case MotionEvent.ACTION_MOVE:
if (clickable) {
drawableHotspotChanged(x, y);
}
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
}
return true;
}
return false;
}
最后通过一张图表示上面的几次实验的结果。