本期三篇文章目錄(可點擊跳轉)
一. Android TouchEvent事件傳遞機制初識
二. Android View 事件分發機制 源碼解析(ViewGroup篇)
三.Android View 事件分發機制 源碼解析(View篇)
- 前言
上一篇介紹了ViewGroup中點擊事件傳遞過程,這篇主要介紹View中如何傳遞點擊事件以及一些注意點。
2.源碼解析
上文中講到,dispatchTransformedTouchEvent方法會調用dispatchTouchEvent方法,點擊事件從ViewGroup成功傳遞到View中,接下來看下dispatchTouchEvent方法的源碼:
/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
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();
}
//當前View是否沒被遮住等
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
//調用onTouch方法,它其實就是OnTouchListener接口的方法
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//onTouch方法返回true,則不執行onTouchEvent(event)方法
//onTouch方法返回false,則執行onTouchEvent(event)方法
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;
}
跟ViewGroup的dispatchTouchEvent方法比起來,View的dispatchTouchEvent方法真是簡單太多了。
1)前面都是一些跟主流程無關的代碼,我們直接看第31行
onFilterTouchEventForSecurity(event)判斷當前View是否沒被遮住,如果沒有被遮擋住,則執行if語句塊中代碼。
2)繼續看第33-39行,onTuouch事件觸發
ListenerInfo是View的靜態內部類,裏面是一些回調接口,比如:OnClickListener,OnLongClickListener等等。
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event))
這個判斷比較長,li是ListenerInfo的對象,已經初始化過了,必然不爲null,li.mOnTouchListener是否爲null呢?全局搜一下,在哪裏初始化或者賦值。在View中搜索到如下代碼:
/**
* Register a callback to be invoked when a touch event is sent to this view.
* @param l the touch listener to attach to this view
*/
public void setOnTouchListener(OnTouchListener l) {
getListenerInfo().mOnTouchListener = l;
}
這個方法,我相信大部分都很熟悉,不就是TextView或者Button在監聽touch事件的時候,需要增加的監聽方法嗎?沒錯,就是他。也就是說我們設置了我們的view 設置了setOnTouchListener(OnTouchListener l)方法後,li.mOnTouchListener則不爲空。反之,如果不設置setOnTouchListener方法,則不執行if語句塊中代碼,則result=false。
接着通過位與運算確定控件(View)是不是enabled的,默認控件都是enabled的,也就是說,如果你調用一個view,設置成view.setEnabled(false),則view的onTouch方法將不會被觸發,onTouchEvent方法則不受影響。
最後,調用li.mOnTouchListener.onTouch(this, event),如果onTouch方法返回true,則result=true,就不執行onTouchEvent(event)方法,反之,則執行onTouchEvent(event)方法。所以一般如果我們在自己的view中設置了setOnTouchListener方法後,並且返回值設置成true後,則當前view就接受不到onTouchEvent(event)方法。
3)繼續看第40-43行,onTouchEvent事件觸發
當result=false是,onTouchEvent被調用,根據result的賦值,可以得到一個結論,dispatchTouchEvent的返回值由onTouch和onTouchEvent返回值決定。
關於onTouchEvent的源碼,繼續跟蹤下去。
onTouchEvent的源碼如下所示:
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
//view是否爲enabled,不管爲true或者false都不影響onTouchEvent方法的返回,但是影響執行過程
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.
//onTouchEvent的返回跟clickable跟longclickable有關,但是如果enabled爲false是,則直接退出了該方法,則onClick無法觸發
return (((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
//onTouchEvent的執行跟clickable跟longclickable有關,
//其實跟enable也有關係,因爲enabled爲false時直接退出方法,下面這段代碼則無法執行
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) {
// 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)) {
performClick();//調用onClick方法
}
}
}
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:
mHasPerformedLongPress = false;
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);
}
break;
case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
setPressed(false);
}
}
break;
}
return true;
}
return false;
}
又是一百多行代碼,繼續看吧。
1)前面都是一些跟主流程無關的代碼,我們直接看第6-17行
這段代碼主要就是判斷view的enabled爲false還是true,通過源碼可以知道,view的enable不管爲true或者false都不影響onTouchEvent方法的返回,但是影響執行過程,onTouchEvent的返回跟clickable跟longclickable有關,但是如果enabled爲false是,則直接退出了該方法,則onClick無法觸發。
2)繼續看24-28行
當clickable跟longclickable都爲true是,則執行switch方法塊,可知onTouchEvent的執行跟clickable跟longclickable有關,其實跟enable也有關係,因爲enabled爲false時直接退出方法,下面這段代碼則無法執行。所以有的時候,你的view的onClick事件監聽不到,看看是否設置了這三個屬性其中之一爲false。
3)繼續看54-62行,通知回調onClick方法
使用Runnable併發布,而不是直接調用performClick。 這使得視圖的其他可視狀態在點擊操作開始之前更新。performClick源碼如下所示:
/**
* Call this view's OnClickListener, if it is defined. Performs all normal
* actions associated with clicking: reporting accessibility event, playing
* a sound, etc.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}
跟前面一樣,li不爲空,而且不難理解li.mOnClickListener肯定是通過setOnClickListener(@Nullable OnClickListener l)設置的。
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);//默認調用該方法,clickable都設置成爲了true
}
getListenerInfo().mOnClickListener = l;
}
當view設置了setOnClickListener方法,則performClick()方法會回調onClick方法。而且performClick()只在MotionEvent.ACTION_UP點擊事件中執行,也就是手指離開屏幕時才執行。
3.總結
1.dispatchTouchEvent方法中,設置了setOnTouchListener跟setOnClickListener方法的時候,先執行onTouch方法,再執行onClick方法。
2.如果onTouch方法返回true,就不執行onTouchEvent(event)方法,反之,則執行onTouchEvent(event)方法。所以一般如果我們在自己的view中設置了setOnTouchListener方法後,並且返回值設置成true後,則當前view就接受不到onTouchEvent(event)方法。
3.view的enable不管爲true或者false都不影響onTouchEvent方法的返回,但是影響執行過程,onTouchEvent的返回跟clickable跟longclickable有關,但是如果enabled爲false是,則直接退出了dispatchTouchEvent方法,則onClick無法觸發,所以有的時候,你的view的onClick事件監聽不到,看看是否設置了這三個屬性其中之一爲false。
4.我們主動調用performClick觸發點擊時,其實就是做的MotionEvent.ACTION_UP執行的事情,作用就是接口回調而已。
如有錯誤歡迎指出來,一起學習。