前言
最近在做项目的过程中，在使用listview的时候遇到了设置item监听事件的时候在没有回调onitemclick 方法的问题。我的情况是在item中有一个button按钮。所以不会回调。上百度找到了解决办法有两种，如下:
1、在checkbox、button对应的view处加android:focusable=”false”
android:clickable=”false” android:focusableintouchmode=”false”
2、在item最外层添加属性 android:descendantfocusability=”blocksdescendants”
网上大多数帖子的理由是：当listview中包含button，checkbox等控件的时候，android会默认将focus给了这些控件，也就是说listview的item根本就获取不到focus，所以导致onitemclick时间不能触发。
由于自己想去验证一下，所有有了这篇文章。好了下面开始
我们为listview设置的onitemclicklistener是在何处回调的?
要搞清楚这个问题，我们先从 android事件分发机制开始说起，事件分发机制网上有大神写了一些特别详细和优秀的文章，在这里就只做简要介绍了：
事件分发重要的三个方法
public boolean dispatchtouchevent(motionevent ev)
该方法用来进行事件分发，在事件传递到当前view的时候调用，返回结果受到当前view的ontouchevent和下级view的dispatchtouchevent方法的影响。
public boolean onintercepttouchevent(motionevent ev)
该方法在上一个方法dispatchtouchevent中调用，返回结果表示是否拦截当前事件，默认返回false，也就是不拦截。
public void ontouchevent(motionevent event)
在 dispatchtouchevent方法中调用，该方法用来处理点击事件,返回结果表示是否消耗当前事件。
当点击事件触发之后的流程
了解事件分发机制之后，我们在setonitemclick之后肯定需要进行事件处理，上面说到事件拦截默认是不拦截，所以我们猜想会到listview的ontouchevent方法中去处理itemclick事件。去找你会发现listview没有ontouchevent方法。那我们再去他的父类abslistview去找。还真有：
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@overridepublic boolean ontouchevent(motionevent ev) {if (!isenabled()) {// a disabled view that is clickable still consumes the touch// events, it just doesn't respond to them.return isclickable() || islongclickable();}if (mpositionscroller != null) {mpositionscroller.stop();}if (misdetaching || !isattachedtowindow()) {// something isn't right.// since we rely on being attached to get data set change notifications,// don't risk doing anything where we might try to resync and find things// in a bogus state.return false;}startnestedscroll(scroll_axis_vertical);if (mfastscroll != null && mfastscroll.ontouchevent(ev)) {return true;}initvelocitytrackerifnotexists();final motionevent vtev = motionevent.obtain(ev);final int actionmasked = ev.getactionmasked();if (actionmasked == motionevent.action_down) {mnestedyoffset = 0;}vtev.offsetlocation(0, mnestedyoffset);switch (actionmasked) {case motionevent.action_down: {ontouchdown(ev);break;}case motionevent.action_move: {ontouchmove(ev, vtev);break;}case motionevent.action_up: {ontouchup(ev);break;}case motionevent.action_cancel: {ontouchcancel();break;}case motionevent.action_pointer_up: {onsecondarypointerup(ev);final int x = mmotionx;final int y = mmotiony;final int motionposition = pointtoposition(x, y);if (motionposition >= 0) {// remember where the motion event startedfinal view child = getchildat(motionposition - mfirstposition);mmotionvieworiginaltop = child.gettop();mmotionposition = motionposition;}mlasty = y;break;}case motionevent.action_pointer_down: {// new pointers take over dragging dutiesfinal int index = ev.getactionindex();final int id = ev.getpointerid(index);final int x = (int) ev.getx(index);final int y = (int) ev.gety(index);mmotioncorrection = 0;mactivepointerid = id;mmotionx = x;mmotiony = y;final int motionposition = pointtoposition(x, y);if (motionposition >= 0) {// remember where the motion event startedfinal view child = getchildat(motionposition - mfirstposition);mmotionvieworiginaltop = child.gettop();mmotionposition = motionposition;}mlasty = y;break;}}if (mvelocitytracker != null) {mvelocitytracker.addmovement(vtev);}vtev.recycle();return true;} |
代码比较长，我们主要看46行 motionevent.action_up的情况，因为onitemclick事件的触发是在我们的手指从屏幕抬起的那一刻，在motionevent.action_up的情况下执行了ontouchup(ev)；那么我们可以想到问题发生的原因应该就是在这个方法了里了。
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private void ontouchup(motionevent ev) {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);if (child != null) {if (mtouchmode != touch_mode_down) {child.setpressed(false);}final float x = ev.getx();final boolean inlist = x > mlistpadding.left && x < getwidth() - mlistpadding.right;if (inlist && !child.hasfocusable()) {if (mperformclick == null) {mperformclick = new performclick();}final abslistview.performclick performclick = mperformclick;performclick.mclickmotionposition = motionposition;performclick.rememberwindowattachcount();mresurrecttoposition = motionposition;if (mtouchmode == touch_mode_down || mtouchmode == touch_mode_tap) {removecallbacks(mtouchmode == touch_mode_down ?mpendingcheckfortap : mpendingcheckforlongpress);mlayoutmode = layout_normal;if (!mdatachanged && madapter.isenabled(motionposition)) {mtouchmode = touch_mode_tap;setselectedpositionint(mmotionposition);layoutchildren();child.setpressed(true);positionselector(mmotionposition, child);setpressed(true);if (mselector != null) {drawable d = mselector.getcurrent();if (d != null && d instanceof transitiondrawable) {((transitiondrawable) d).resettransition();}mselector.sethotspot(x, ev.gety());}if (mtouchmodereset != null) {removecallbacks(mtouchmodereset);}mtouchmodereset = new runnable() {@overridepublic void run() {mtouchmodereset = null;mtouchmode = touch_mode_rest;child.setpressed(false);setpressed(false);if (!mdatachanged && !misdetaching && isattachedtowindow()) {performclick.run();}}};postdelayed(mtouchmodereset,viewconfiguration.getpressedstateduration());} else {mtouchmode = touch_mode_rest;updateselectorstate();}return;} else if (!mdatachanged && madapter.isenabled(motionposition)) {performclick.run();}}}mtouchmode = touch_mode_rest;updateselectorstate();break;｝ |
这里主要看7行到18行，拿到了我们item的view,并且在15行代码里判断了item的view是否在范围是否获取焦点（hasfocusable()），这里对hasfocusable()取反判断，也就是说，必需要我们的itemview的hasfocusable（） 方法返回false, 才会执行一下的方法，以下的方法就是点击事件的方法。那么我们来看看是不是mperformclick真的就是执行我们的itemclick事件。
performclick以及相关代码如下：
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private class performclick extends windowrunnnable implements runnable {int mclickmotionposition;@overridepublic void run() {// the data has changed since we posted this action in the event queue,// bail out before bad things happenif (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 clickif (view != null) {performitemclick(view, motionposition, adapter.getitemid(motionposition));}}}} |
第18行代码拿到了我们点击的item view,并且调用了performitemclick方法。我们再来看abslistview的performitemclick方法：
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@overridepublic boolean performitemclick(view view, int position, long id) {boolean handled = false;boolean dispatchitemclick = true;if (mchoicemode != choice_mode_none) {handled = true;boolean checkedstatechanged = false;if (mchoicemode == choice_mode_multiple ||(mchoicemode == choice_mode_multiple_modal && mchoiceactionmode != null)) {boolean checked = !mcheckstates.get(position, false);mcheckstates.put(position, checked);if (mcheckedidstates != null && madapter.hasstableids()) {if (checked) {mcheckedidstates.put(madapter.getitemid(position), position);} else {mcheckedidstates.delete(madapter.getitemid(position));}}if (checked) {mcheckeditemcount++;} else {mcheckeditemcount--;}if (mchoiceactionmode != null) {mmultichoicemodecallback.onitemcheckedstatechanged(mchoiceactionmode,position, id, checked);dispatchitemclick = false;}checkedstatechanged = true;} else if (mchoicemode == choice_mode_single) {boolean checked = !mcheckstates.get(position, false);if (checked) {mcheckstates.clear();mcheckstates.put(position, true);if (mcheckedidstates != null && madapter.hasstableids()) {mcheckedidstates.clear();mcheckedidstates.put(madapter.getitemid(position), position);}mcheckeditemcount = 1;} else if (mcheckstates.size() == 0 || !mcheckstates.valueat(0)) {mcheckeditemcount = 0;}checkedstatechanged = true;}if (checkedstatechanged) {updateonscreencheckedviews();}}if (dispatchitemclick) {handled |= super.performitemclick(view, position, id);}return handled;} |
看第54行调用了父类的performitemclick方法：
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public boolean performitemclick(view view, int position, long id) {final boolean result;if (monitemclicklistener != null) {playsoundeffect(soundeffectconstants.click);monitemclicklistener.onitemclick(this, view, position, id);result = true;} else {result = false;}if (view != null) {view.sendaccessibilityevent(accessibilityevent.type_view_clicked);}return result;} |
好了，搞了半天，终于到点上了。第3
行代码很明显了，就是如果有itemclicklistener，就执行他的onitemclick方法，最终回调到我们常见的那个方法。
到这里，相信大家已经知道，关键代码就是刚才上面我们分析的那一个if判断
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if (inlist && !child.hasfocusable()) {if (mperformclick == null) {mperformclick = new performclick();}.....｝ |
也就是只有item的view hasfocusable( )方法返回false,才会执行onitemclick。
view 和 viewgroup 的 hasfocusable
viewgroup的hasfocusable
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@overridepublic 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;} |
看源码我们可以知道：
如果 viewgroup visiable 和 focusable 都为 true，就算能够获取焦点， 返回 true。
如果我们给viewgroup设置了descendantfocusability属性，并且等于focus_block_descendants的情况下，返回false。不能获取焦点。
如果没有设置descendantfocusability属性的话，只要一个子view hasfocusable返回了true,viewgroup的hasfocusable就返回。
再来看view的hasfocusable
viewgroup的hasfocusable
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public boolean hasfocusable() {if (!isfocusableintouchmode()) {for (viewparent p = mparent; p instanceof viewgroup; p = p.getparent()) {final viewgroup g = (viewgroup) p;if (g.shouldblockfocusfortouchscreen()) {return false;}}}return (mviewflags & visibility_mask) == visible && isfocusable();} |
在触摸模式下如果不可获取焦点，先遍历 view 的所有父节点，如果有一个父节点设置了阻塞子 view 获取焦点，那么该 view 就不可能获取焦点
在触摸模式下如果不可获取焦点，并且没有父节点设置阻塞子 view 获取焦点，和在触摸模式下如果可以获取焦点，那么才判断 view 自身的 visiable 和 focusable 属性，来决定是否可以获取焦点,只有 visiable 和 focusable 同时为 true，该view 才可能获取焦点。
好了，分析到这里我们再回过头去看两个解决办法。
在checkbox、button对应的view处加android:focusable=”false”
android:clickable=”false” android:focusableintouchmode=”false”
在item最外层添加属性 android:descendantfocusability=”blocksdescendants”
第一种情况，item没有设置descendantfocusability=”blocksdescendants”，遍历了所有子view,由于所有的子view都不可获得焦点，所有item也没有获取焦点，那么上面说到回调至性的条件判断也就的代码：
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if (inlist && !child.hasfocusable()) {if (mperformclick == null) {mperformclick = new performclick();}.....｝ |
if条件成立，所有执行了回调。
第二种情况，item,设置了descendantfocusability=”blocksdescendants”，所有没有遍历子 view,child.hasfocusable()直接返回false了。
以上所述是本文给大家分享的android 中listview setonitemclicklistener点击无效原因分析，希望大家喜欢。
