編輯：關於android開發
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”
android:clickable=”false” android:focusableInTouchMode=”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。
由於自己想去驗證一下，所有有了這篇文章。好了下面開始
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，在這裡就只做簡要介紹了：
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。
了解事件分發機制之後，我們在setOnItemClick之後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：
@Override
public 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 started
final View child = getChildAt(motionPosition - mFirstPosition);
mMotionViewOriginalTop = child.getTop();
mMotionPosition = motionPosition;
}
mLastY = y;
break;
}
case MotionEvent.ACTION_POINTER_DOWN: {
// New pointers take over dragging duties
final 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 started
final 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)；那麼我們可以想到問題發生的原因應該就是在這個方法了裡了。
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() {
@Override
public 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;
｝
這裡主要看7行到18行，拿到了我們item的View,並且在15行代碼裡判斷了item的View是否在范圍是否獲取焦點（hasFocusable()），這裡對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。那麼我們來看看是不是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;
@Override
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));
}
}
}
}
第18行代碼拿到了我們點擊的item View,並且調用了performItemClick方法。我們再來看absListView的performItemClick方法：
@Override
public 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，終於到點上了。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。
到這裡，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。
源碼
@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;
}
看源碼我們可以知道：
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();
}
好了，分析到這裡我們再回過頭去看兩個解決辦法。
第一種情況，item沒有設置descendantFocusability=”blocksDescendants”，遍歷了所有子View,由於所有的子view都不可獲得焦點，所有item也沒有獲取焦點，那麼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。
好了，分析到這裡相信大家已經很明白了。
如有對你有幫助，請各位大俠點下面的評論或點贊。如有錯誤請輕噴。。。。
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