维护方向更改时的项目选择

Question

我正在尝试恢复方向更改的操作模式的状态.但它不能正常工作.按照以下步骤顺序,在#3和#4中,选择被破坏:

1. 长按项目 - 项目突出显示,上下文操作栏显示标题显示"1选中".看起来不错.
2. 将手机转为风景 - 没有变化.看起来不错.
3. 将手机设置为纵向 - 项目未突出显示,上下文操作栏消失
4. 长按项目 - 项目突出显示,上下文操作栏显示标题显示"0已选中"

myListView.getCheckedItemCount()在onSaveInstanceState()#3上返回0.这就是问题开始的地方.

我的片段(使用支持库)我做错了什么？

@Override
public void onSaveInstanceState(Bundle outState) {
    //check if any items are selected
    if (myListView.getCheckedItemCount() > 0) {
        //get the list of selected items and convert it to an int Array
        //because SparseBooleanArray cannot be stored in a bundle
        SparseBooleanArray selectedItems = myListView.getCheckedItemPositions();
        int[] selectedItems_intArray = new int[myListView.getCheckedItemCount()];
        for (int i = 0; i < selectedItems.size(); i++) {
            if (selectedItems.valueAt(i) == false)
                continue;
            selectedItems_intArray[i] = selectedItems.keyAt(i);
        }
        outState.putIntArray(KEY_CHECKED_ITEMS, selectedItems_intArray);
    }
}

@Override
public void onViewStateRestored(Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    if (savedInstanceState != null) {
        int[] checkedItems = savedInstanceState.getIntArray(KEY_CHECKED_ITEMS);
        if (checkedItems != null) {
            actionMode = ((ActionBarActivity) getActivity()).startSupportActionMode(new ContextualActionBarActionModeCallBack());

            for (int i = 0; i < checkedItems.length; i++) {
                myListView.setItemChecked(checkedItems[i], true);
            }

            actionMode.setTitle(myListView.getCheckedItemCount() + " selected");
        }
    }
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    myListView = (ListView) getActivity().findViewById(R.id.myListView);
    adpt = new myCustomCursorAdapter(getActivity());
    myListView.setAdapter(adpt);
    //Choice mode is allowed only after a long click
    //disabling it on first time load
    myListView.setChoiceMode(ListView.CHOICE_MODE_NONE);
        myListView.setOnItemLongClickListener(new OnItemLongClickListener(){
        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id){
            if(actionMode == null){
                //Start the action mode
                actionMode = ((ActionBarActivity)getActivity()).startSupportActionMode(new ContextualActionBarActionModeCallBack());

                myLisVIew.setItemChecked(position, true);                           
                actionMode.setTitle(myListView.getCheckedItemCount() + " selected");
                return true;
                }
            else return false;
        }
    });
}

@Override
public void onResume(){
    super.onResume();
    getLoaderManager().initLoader(0,null,this);
}

private class ContextualActionBarActionModeCallBack implements ActionMode.Callback{
    @Override
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        MenuInflater inflater = mode.getMenuInflater();
        inflater.inflate(R.menu.mycontextmenu, menu);   
        myListView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
    }
    ...
    ...
}

ListView布局元素:

<ListView
        android:id="@+id/myListView"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:layout_alignParentTop="true"
        android:listSelector="@android:color/transparent"
        android:stackFromBottom="true"
        android:layout_above="@id/layout_input"
        android:divider="#00000000"
        />

Answer 1

问题是列表视图的选择模式正在重置为CHOICE_MODE_NONE每次在方向更改时创建列表视图时的默认值,因为未在列表视图布局文件中明确定义选择模式.发生这种情况的Android源代码 - http://androidxref.com/4.4.2_r2/xref/frameworks/base/core/java/android/widget/AbsListView.java#815.

解决方案是添加:

android:choiceMode="multipleChoice"

到列表视图布局.

这也意味着无需手动存储列表视图选择onSaveInstanceState()并将其检索到onViewStateRestored().它由片段自动完成.所以删除这两个功能.只需启动动作模式onResume:

@Override
    public void onResume() {
        super.onResume();
            getLoaderManager().initLoader(0,null,this);
            if (myListView.getCheckedItemCount() > 0 && actionMode == null) {
            actionMode = ((ActionBarActivity) getActivity()).startSupportActionMode(new ContextualActionBarActionModeCallBack());
            actionMode.setTitle(myListView.getCheckedItemCount() + " selected");
        }
    }

注意:如果已实现LoaderManager.LoaderCallBacks接口,并且需要在方向更改后访问适配器项,请在onLoadFinished()适配器加载数据源后执行此操作.这样做onResume()会导致NPE.