前言
最近在做項目的過程中，在使用listview的時候遇到了設置item監聽事件的時候在沒有回調onItemClick 方法的問題。我的情況是在item中有一個Button按鈕。所以不會回調。上百度找到了解決辦法有兩種，如下:
1、在checkbox、button對應的view處加android:focusable=”false”
2、在item最外層添加屬性 android:descendantFocusability=”blocksDescendants”
網上大多數帖子的理由是：當listview中包含button，checkbox等控件的時候，android會默認將focus給了這些控件，也就是說listview的item根本就獲取不到focus，所以導致onitemclick時間不能觸發。
由于自己想去驗證一下，所有有了這篇文章。好了下面開始
我們為ListView設置的onItemClickListener是在何處回調的?
要搞清楚這個問題，我們先從 android事件分發機制開始說起，事件分發機制網上有大神寫了一些特別詳細和優秀的文章，在這里就只做簡要介紹了：
事件分發重要的三個方法
該方法用來進行事件分發，在事件傳遞到當前View的時候調用，返回結果受到當前View的onTouchEvent和下級View的dispatchTouchEvent方法的影響。
該方法在上一個方法dispatchTouchEvent中調用，返回結果表示是否攔截當前事件，默認返回false，也就是不攔截。
在 dispatchTouchEvent方法中調用，該方法用來處理點擊事件,返回結果表示是否消耗當前事件。
當點擊事件觸發之后的流程
了解事件分發機制之后，我們在setOnItemClick之后肯定需要進行事件處理，上面說到事件攔截默認是不攔截，所以我們猜想會到ListView的onTouchEvent方法中去處理ItemClick事件。去找你會發現ListView沒有onTouchEvent方法。那我們再去他的父類AbsListView去找。還真有：
@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;}代碼比較長，我們主要看46行 MotionEvent.ACTION_UP的情況，因為onItemClick事件的觸發是在我們的手指從屏幕抬起的那一刻，在MotionEvent.ACTION_UP的情況下執行了onTouchUp(ev)；那么我們可以想到問題發生的原因應該就是在這個方法了里了。
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;｝這里主要看7行到18行，拿到了我們item的View,并且在15行代碼里判斷了item的View是否在范圍是否獲取焦點（hasFocusable()），這里對hasFocusable()取反判斷，也就是說，必需要我們的itemView的hasFocusable（） 方法返回false, 才會執行一下的方法，以下的方法就是點擊事件的方法。那么我們來看看是不是mPerformClick真的就是執行我們的itemClick事件。
PerformClick以及相關代碼如下：
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行代碼拿到了我們點擊的item View,并且調用了performItemClick方法。我們再來看absListView的performItemClick方法：
@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行調用了父類的performItemClick方法：
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，終于到點上了。第3
行代碼很明顯了，就是如果有ItemClickListener，就執行他的onItemClick方法，最終回調到我們常見的那個方法。
到這里，相信大家已經知道，關鍵代碼就是剛才上面我們分析的那一個if判斷
if (inList && !child.hasFocusable()) {if (mPerformClick == null) {mPerformClick = new PerformClick();}.....｝也就是只有item的View hasFocusable( )方法返回false,才會執行onItemClick。
View 和 ViewGroup 的 hasFocusable
ViewGroup的hasFocusable
@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;}看源碼我們可以知道：
如果 ViewGroup visiable 和 focusable 都為 true，就算能夠獲取焦點， 返回 true。
如果我們給ViewGroup設置了descendantFocusability屬性，并且等于FOCUS_BLOCK_DESCENDANTS的情況下，返回false。不能獲取焦點。
如果沒有設置descendantFocusability屬性的話，只要一個子View hasFocusable返回了true,ViewGroup的hasFocusable就返回。
再來看View的hasFocusable
ViewGroup的hasFocusable
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();}在觸摸模式下如果不可獲取焦點，先遍歷 View 的所有父節點，如果有一個父節點設置了阻塞子 View 獲取焦點，那么該 View 就不可能獲取焦點
在觸摸模式下如果不可獲取焦點，并且沒有父節點設置阻塞子 View 獲取焦點，和在觸摸模式下如果可以獲取焦點，那么才判斷 View 自身的 visiable 和 focusable 屬性，來決定是否可以獲取焦點,只有 visiable 和 focusable 同時為 true，該View 才可能獲取焦點。
好了，分析到這里我們再回過頭去看兩個解決辦法。
在checkbox、button對應的view處加android:focusable=”false”
在item最外層添加屬性 android:descendantFocusability=”blocksDescendants”
第一種情況，item沒有設置descendantFocusability=”blocksDescendants”，遍歷了所有子View,由于所有的子view都不可獲得焦點，所有item也沒有獲取焦點，那么上面說到回調至性的條件判斷也就的代碼：
if (inList && !child.hasFocusable()) {if (mPerformClick == null) {mPerformClick = new PerformClick();}.....｝if條件成立，所有執行了回調。
第二種情況，item,設置了descendantFocusability=”blocksDescendants”，所有沒有遍歷子 View,child.hasFocusable()直接返回false了。
以上所述是本文給大家分享的Android 中ListView setOnItemClickListener點擊無效原因分析，希望大家喜歡。
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