工程里原来的代码执行如下操作 在android6.0以下运行良好:
@Override
public void onListItemClick(ListView lv, View view, int position, long id) {
....
position -= mList.getHeaderViewsCount();
if (mAdapter.isInChoiceMode()) {
setListItemChecked(position);
return;
}
...
}
public void setListItemChecked(int position) {
boolean checked = mList.isItemChecked(position);
mList.setItemChecked(position, checked);
...
}
首先以上代码槽点比较多 一会再说。
而工程适配android7.0(24)时发现点击item之后显示的选择状态不更新,Item有被选择上,只不过view没更新。
以上代码第一个槽点:
position -= mList.getHeaderViewsCount();
boolean checked = mList.isItemChecked(position);
mList.isItemChecked(position)的position应该是包含了list的header,所以这里减去Header数量就不对了。
第二个槽点:
boolean checked = mList.isItemChecked(position);
mList.setItemChecked(position, checked);
首先这两句的逻辑看似是重复的,根据以前使用ListView选择模式的经验,正常点击操作不用调用setItemChecked(),ListView内部逻辑就会将点击事件处理,进行选择。
读源码,相关逻辑如下:
@Override
public boolean onTouchEvent(MotionEvent ev) {
...
case MotionEvent.ACTION_UP: {
onTouchUp(ev);
break;
}
...
}
最终调用到了:AbsListView.performItemClick():
@Override
public boolean performItemClick(View view, int position, long id) {
...
//mCheckedIdStates修改
...
if (dispatchItemClick) {
handled |= super.performItemClick(view, position, id);
}
return handled;
}
return handled;
}
父类的该方法:
AdaperView.performItemClick():
public boolean performItemClick(View view, int position, long id) {
if (mOnItemClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
mOnItemClickListener.onItemClick(this, view, position, id);
if (view != null) {
view.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
}
return true;
}
return false;
}
所以是先修改了mCheckedIdStates,再调用了mOnItemClickListener的onItemClick方法,所以在 boolean checked = mList.isItemChecked(position)之后调用mList.setItemChecked(position, checked)对保存选取结果无意义。
为何代码在Android 6.0及一下能正常运行,而在7.0以上不行?
首先看6.0和7.0的setItemChecked方法的对比:
android 7.0(24): AbsListView.setItemChecked()
public void setItemChecked(int position, boolean value) {
...
if (mChoiceMode == CHOICE_MODE_MULTIPLE || mChoiceMode == CHOICE_MODE_MULTIPLE_MODAL) {
itemCheckChanged = oldValue != value;
// Do not generate a data change while we are in the layout phase or data has not changedif (!mInLayout && !mBlockLayoutRequests && itemCheckChanged) {
mDataChanged = true;
rememberSyncState();
requestLayout();
}
}
android 6.0(23): AbsListView.setItemChecked()
public void setItemChecked(int position, boolean value) {
// Do not generate a data change while we are in the layout phase
if (!mInLayout && !mBlockLayoutRequests) {
mDataChanged = true;
rememberSyncState();
requestLayout();
}
}
以上可见,区别在于6.0时,当点击状态不变时也会调用requestLayout(),而7.0开始只有item的选择状态发生改变时才会调用requestLayout()进行重绘。
boolean checked = mList.isItemChecked(position);
mList.setItemChecked(position, checked);
这两句不会改变item的选择状态,所以在7.0后就不会使List重绘了。
那么使用ListView的ChoiceMode的正确姿势是什么呢?
看两段相关代码
AbsListView.updateOnScreenCheckedViews()
/** * Perform a quick, in-place update of the checked or activated state * on all visible item views. This should only be called when a valid * choice mode is active. */
private void updateOnScreenCheckedViews() {
final int firstPos = mFirstPosition;
final int count = getChildCount();
final boolean useActivated = getContext().getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.HONEYCOMB;
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
final int position = firstPos + i;
if (child instanceof Checkable) {
((Checkable) child).setChecked(mCheckStates.get(position));
}
else if (useActivated) {
child.setActivated(mCheckStates.get(position));
}
}
}
该方法在performItemClick()里被调用。
ListView.setupChild()
private void setupChild(View child, int position, int y, boolean flowDown, int childrenLeft, boolean selected, boolean recycled) {
if (mChoiceMode != CHOICE_MODE_NONE && mCheckStates != null) {
if (child instanceof Checkable) {
((Checkable) child).setChecked(mCheckStates.get(position));
} else if (getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB) { child.setActivated(mCheckStates.get(position));
}
}
setupChild()在其item绘制时候会被调用。
所以,让ItemView实现Checkable接口,在Item被选择后就会调用该接口的setChecked方法。
改造后的ItemView大致如此:
public abstract class ItemView extends LinearLayout implements Checkable{
...
public CheckBox mCheckBox;
private boolean isChecked;
@Override
public void setChecked(boolean isItemChecked) {
this.isChecked = checked;
mCheckBox.setChecked(isItemChecked);
}
@Override
public boolean isChecked() {
return isChecked;
}
@Override
public void toggle() {
setChecked(!isChecked);
}
}
checkbox不能再响应它自身的点击事件了: 清除焦点并设为不可点击
<CheckBox
android:id="@android:id/checkbox"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:focusable="false"
android:clickable="false" />
此外,另一种实现ChoiceMode的方法是在OnItemClick()里和getView()里,根据 mList.isItemChecked(position)来设置checkbox 。但这种方法并不推荐,因为这是在点击和绘制时单独处理checkbox的逻辑。
另外一种是在OnItemClick里直接notifyDataChange()重绘,getView()里根据 mList.isItemChecked(position)来设置checkbox。而这种方法又重新绘制了ListView,开销更大。
还是让ItemView实现checkable接口比较好,绘制次数更少,逻辑更清晰。