Android android开发 Selector

Pressed状态和clickable,duplicateParentState的关系

2019-01-08
5次浏览

??????? 做Android开发的人都用过Selector,可以方便的实现View在不同状态下的背景。不过,相信大部分开发者遇到过和我一样的问题,本文会从源码角度,解释这些问题。


??????? 首先,这里简单描述一下,我遇到的问题:

界面上有个全屏的LinearLayout A,A中有一个TextView B和Button C,其中,A的clickable=true,并设置了pressed时,背景色为灰色,B设置了pressed时,背景色为蓝色

当手指触摸C下方的空白区域时,看到了这样的效果:

??????? 在这里看到,在没有触摸B的情况下,B的pressed = true,而C的pressed = false。 C的状态暂且不讨论,按照Android消息传递的原则,因为touch的point不在B内部,所以,touch消息应该不会交给B处理,那为什么B的pressed = true?

???????? 下面开始一步一步分析(本文分析的Android源码为4.2.2)。

Pressed状态的设定

??????? 从View.onTouchEvent函数看起(frameworks/base/core/java/android/view/View.java):


????/**
?????*?Implement?this?method?to?handle?touch?screen?motion?events.
?????*
?????*?@param?event?The?motion?event.
?????*?@return?True?if?the?event?was?handled,?false?otherwise.
?????*/
????public?boolean?onTouchEvent(MotionEvent?event)?{
????????......
????????if?(((viewFlags?&?CLICKABLE)?==?CLICKABLE?||?//这里是为什么设置A的clickable为true的原因,否则,press?A的时候,没有界面元素处理touch?event,最终会由Activity的onTouchEvent函数处理
????????????????(viewFlags?&?LONG_CLICKABLE)?==?LONG_CLICKABLE))?{
????????????switch?(event.getAction())?{
????????????????case?MotionEvent.ACTION_UP:
????????????????????......
????????????????????break;

????????????????case?MotionEvent.ACTION_DOWN:
????????????????????mHasPerformedLongPress?=?false;
????????????????????......
????????????????????//?Walk?up?the?hierarchy?to?determine?if?we're?inside?a?scrolling?container.
????????????????????boolean?isInScrollingContainer?=?isInScrollingContainer();//A已经是顶层元素了,没有ScrollView之类的控件存在,所以,isInScrollingContainer?=?false

????????????????????//?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();
????????????????????????}
????????????????????????postDelayed(mPendingCheckForTap,?ViewConfiguration.getTapTimeout());
????????????????????}?else?{
????????????????????????//?Not?inside?a?scrolling?container,?so?show?the?feedback?right?away
????????????????????????setPressed(true);//A设置pressed?=?true
????????????????????????checkForLongClick(0);
????????????????????}
????????????????????break;

????????????????case?MotionEvent.ACTION_CANCEL:
????????????????????......
????????????????????break;

????????????????case?MotionEvent.ACTION_MOVE:
????????????????????......
????????????????????break;
????????????}
????????????return?true;
????????}

????????return?false;
????}

???????

??????? 从上面的代码我们知道,当手指触摸A的时候,A的pressed被设置为true。

Pressed状态的传递

??????? 接着,我们看看setPressed函数的实现:


????/**
?????*?Sets?the?pressed?state?for?this?view.
?????*
?????*?@param?pressed?Pass?true?to?set?the?View's?internal?state?to?"pressed",?or?false?to?reverts
?????*????????????????the?View's?internal?state?from?a?previously?set?"pressed"?state.
?????*?@see?#isClickable()
?????*?@see?#setClickable(boolean)
?????*/
????public?void?setPressed(boolean?pressed)?{
????????final?boolean?needsRefresh?=?pressed?!=?((mPrivateFlags?&?PFLAG_PRESSED)?==?PFLAG_PRESSED);

????????if?(pressed)?{
????????????mPrivateFlags?|=?PFLAG_PRESSED;
????????}?else?{
????????????mPrivateFlags?&=?~PFLAG_PRESSED;
????????}

????????if?(needsRefresh)?{
????????????refreshDrawableState();//切换背景图片
????????}
????????dispatchSetPressed(pressed);
????}

??????? setPressed函数内部调用了dispatchSetPressed函数,这个让人很在意(frameworks/base/core/java/android/view/ViewGroup.java):



????@Override
????protected?void?dispatchSetPressed(boolean?pressed)?{
????????final?View[]?children?=?mChildren;
????????final?int?count?=?mChildrenCount;
????????for?(int?i?=?0;?i?<?count;?i++)?{
????????????final?View?child?=?children[i];
????????????//?Children?that?are?clickable?on?their?own?should?not
????????????//?show?a?pressed?state?when?their?parent?view?does.
????????????//?Clearing?a?pressed?state?always?propagates.
????????????if?(!pressed?||?(!child.isClickable()?&&?!child.isLongClickable()))?{
????????????????child.setPressed(pressed);
????????????}
????????}
????}

??????? 原来,dispatchSetPressed函数会把pressed状态传递给所有clickable=false并且longclickable=false的子元素。


??????? 到这里,前面的现象就可以解释了,因为C是button类,clickable=true,而B的clickable=false。所以,当A被触摸时,B的pressed=true,而C的pressed=false。那么,可以回答下面几个小问题了:

如果不希望A的pressed=true时,B的pressed = true,该如何修改? 设置B的clickable=true如果希望A的pressed = true时,C的pressed = true,那又该如何修改? 设置C的clickable = false. 但是,这里可能又存在问题了,设置C的clickable=false,会导致button按钮的onclicklistener无法工作,这是个严重的副作用。那么可以不修改clickable,而设置android:duplicateParentState为true。

?????? 那么duplicateParentState做了些什么呢?View.setDuplicateParentStateEnabled:


????public?void?setDuplicateParentStateEnabled(boolean?enabled)?{
????????setFlags(enabled???DUPLICATE_PARENT_STATE?:?0,?DUPLICATE_PARENT_STATE);
????}

????? 再看看View.onCreateDrawableState()



?/**
?????*?Generate?the?new?{@link?android.graphics.drawable.Drawable}?state?for
?????*?this?view.?This?is?called?by?the?view
?????*?system?when?the?cached?Drawable?state?is?determined?to?be?invalid.??To
?????*?retrieve?the?current?state,?you?should?use?{@link?#getDrawableState}.
?????*
?????*?@param?extraSpace?if?non-zero,?this?is?the?number?of?extra?entries?you
?????*???????????????????would?like?in?the?returned?array?in?which?you?can?place?your?own
?????*???????????????????states.
?????*?@return?Returns?an?array?holding?the?current?{@link?Drawable}?state?of
?????*?the?view.
?????*?@see?#mergeDrawableStates(int[],?int[])
?????*/
????protected?int[]?onCreateDrawableState(int?extraSpace)?{
????????if?((mViewFlags?&?DUPLICATE_PARENT_STATE)?==?DUPLICATE_PARENT_STATE?&&
????????????????mParent?instanceof?View)?{
????????????return?((View)?mParent).onCreateDrawableState(extraSpace);
????????}

????????......
????}

??????? 从上面的代码,可以看到,当设置duplicateParentState为true时,View的DrawableState直接使用了其parent的。所以,他的drawable状态会一直保持与其parent同步。

题外,为什么当ListView中包含focusable为true的控件时,OnItemClickListener不会触发

??????? 因为ListView未重载onTouchEvent事件,所以,需要看其父类的AbsListView.onTouchEvent(frameworks/base/core/java/android/widget/AbsListView):


????@Override
????public?boolean?onTouchEvent(MotionEvent?ev)?{
????????......
????????switch?(action?&?MotionEvent.ACTION_MASK)?{
????????case?MotionEvent.ACTION_DOWN:?{
????????????......
????????????break;
????????}

????????case?MotionEvent.ACTION_MOVE:?{
????????????......
????????????break;
????????}

????????case?MotionEvent.ACTION_UP:?{
????????????switch?(mTouchMode)?{
????????????case?TOUCH_MODE_DOWN:
????????????case?TOUCH_MODE_TAP:
????????????case?TOUCH_MODE_DONE_WAITING:
????????????????final?int?motionPosition?=?mMotionPosition;
????????????????final?View?child?=?getChildAt(motionPosition?-?mFirstPosition);

????????????????final?float?x?=?ev.getX();
????????????????final?boolean?inList?=?x?>?mListPadding.left?&&?x?<?getWidth()?-?mListPadding.right;

????????????????if?(child?!=?null?&&?!child.hasFocusable()?&&?inList)?{
????????????????????if?(mTouchMode?!=?TOUCH_MODE_DOWN)?{
????????????????????????child.setPressed(false);
????????????????????}

????????????????????if?(mPerformClick?==?null)?{
????????????????????????mPerformClick?=?new?PerformClick();
????????????????????}

????????????????????......
????????????????????performClick.run();
????????????????????......
????????????????}
????????????????......
????????????case?TOUCH_MODE_SCROLL:
????????????????......
????????????????break;

????????????case?TOUCH_MODE_OVERSCROLL:
????????????......
????????????break;
????????}
????????......
????????case?MotionEvent.ACTION_CANCEL:?{
????????????......
????????????break;
????????}

????????case?MotionEvent.ACTION_POINTER_UP:?{
????????????......
????????????break;
????????}

????????case?MotionEvent.ACTION_POINTER_DOWN:?{
????????????......
????????????break;
????????}
????????}

????????return?true;
????}

???????? 仅在child.hasFocusable()=false时, PerformClick对象才会执行ViewGroup.hasFocusable:


????/**
?????*?{@inheritDoc}
?????*/
????@Override
????public?boolean?hasFocusable()?{
????????if?((mViewFlags?&?VISIBILITY_MASK)?!=?VISIBLE)?{
????????????return?false;
????????}

????????if?(isFocusable())?{
????????????return?true;
????????}

????????final?int?descendantFocusability?=?getDescendantFocusability();
????????if?(descendantFocusability?!=?FOCUS_BLOCK_DESCENDANTS)?{
????????????final?int?count?=?mChildrenCount;
????????????final?View[]?children?=?mChildren;

????????????for?(int?i?=?0;?i?<?count;?i++)?{
????????????????final?View?child?=?children[i];
????????????????if?(child.hasFocusable())?{
????????????????????return?true;
????????????????}
????????????}
????????}

????????return?false;
????}

??????? 仅在所有的clild的hasFocusable为false时,ListView才会执行performClick(AbsListView.PerformClick):



????private?class?PerformClick?extends?WindowRunnnable?implements?Runnable?{
????????int?mClickMotionPosition;

????????public?void?run()?{
????????????//?The?data?has?changed?since?we?posted?this?action?in?the?event?queue,
????????????//?bail?out?before?bad?things?happen
????????????if?(mDataChanged)?return;

????????????final?ListAdapter?adapter?=?mAdapter;
????????????final?int?motionPosition?=?mClickMotionPosition;
????????????if?(adapter?!=?null?&&?mItemCount?>?0?&&
????????????????????motionPosition?!=?INVALID_POSITION?&&
????????????????????motionPosition?<?adapter.getCount()?&&?sameWindow())?{
????????????????final?View?view?=?getChildAt(motionPosition?-?mFirstPosition);
????????????????//?If?there?is?no?view,?something?bad?happened?(the?view?scrolled?off?the
????????????????//?screen,?etc.)?and?we?should?cancel?the?click
????????????????if?(view?!=?null)?{
????????????????????performItemClick(view,?motionPosition,?adapter.getItemId(motionPosition));
????????????????}
????????????}
????????}
????}

??????? 而PerformClick会调用performItemClick(AdsListView.performItemClick):



?@Override
????public?boolean?performItemClick(View?view,?int?position,?long?id)?{
????????boolean?handled?=?false;
????????boolean?dispatchItemClick?=?true;

????????......

????????if?(dispatchItemClick)?{
????????????handled?|=?super.performItemClick(view,?position,?id);
????????}

????????return?handled;
????}

?????? AdapterView.preformItemClick:


????/**
?????*?Call?the?OnItemClickListener,?if?it?is?defined.
?????*
?????*?@param?view?The?view?within?the?AdapterView?that?was?clicked.
?????*?@param?position?The?position?of?the?view?in?the?adapter.
?????*?@param?id?The?row?id?of?the?item?that?was?clicked.
?????*?@return?True?if?there?was?an?assigned?OnItemClickListener?that?was
?????*?????????called,?false?otherwise?is?returned.
?????*/
????public?boolean?performItemClick(View?view,?int?position,?long?id)?{
????????if?(mOnItemClickListener?!=?null)?{
????????????playSoundEffect(SoundEffectConstants.CLICK);
????????????if?(view?!=?null)?{
????????????????view.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
????????????}
????????????mOnItemClickListener.onItemClick(this,?view,?position,?id);
????????????return?true;
????????}

????????return?false;
????}


??????? 所以,如果ListView item中包含focusable为true的控件(例如:button, radiobutton),会导致ItemClickListener失效。开奖预测两个:


设置特定的控件focusable = false

不使用onItemClickListener,而直接在Item上设置onClickListener监听点击事件。





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