使用 CursorAdapter 关闭 Cursor 会导致后台片段出现 StaleDataException

Question

这是对我在这里的问题的跟进：

响应解决了 "Cursor finalized without prior close" 警告，但它在非常特殊的情况下导致了 StaleDataException。

如果列表已经滚动，则此游标关闭...

Cursor cursor = null;
cursor = (Cursor) getListView().getItemAtPosition(n);
//do something
if(cursor != null) {
    cursor.close();
}

和背景片段我得到以下错误：

09-15 21:16:58.240: E/test(21621): Exception
 FATAL EXCEPTION: main
 android.database.StaleDataException: Attempted to access a cursor after it has been closed.
    at android.database.BulkCursorToCursorAdaptor.throwIfCursorIsClosed(BulkCursorToCursorAdaptor.java:64)
    at android.database.BulkCursorToCursorAdaptor.getCount(BulkCursorToCursorAdaptor.java:70)
    at android.database.AbstractCursor.moveToPosition(AbstractCursor.java:196)
    at android.database.CursorWrapper.moveToPosition(CursorWrapper.java:162)
    at android.support.v4.widget.CursorAdapter.getItemId(CursorAdapter.java:225)
    at android.widget.AbsListView.onSaveInstanceState(AbsListView.java:1782)
    at android.view.View.dispatchSaveInstanceState(View.java:11950)
    at android.view.ViewGroup.dispatchFreezeSelfOnly(ViewGroup.java:2685)
    at android.widget.AdapterView.dispatchSaveInstanceState(AdapterView.java:782)
    at android.view.ViewGroup.dispatchSaveInstanceState(ViewGroup.java:2671)
    at android.view.View.saveHierarchyState(View.java:11933)
    at android.support.v4.app.FragmentManagerImpl.saveFragmentViewState(FragmentManager.java:1608)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1004)
    at android.support.v4.app.FragmentManagerImpl.removeFragment(FragmentManager.java:1212)
    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:639)
    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
    at android.support.v4.app.FragmentManagerImpl.run(FragmentManager.java:446)
    at android.os.Handler.handleCallback(Handler.java:615)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4793)

这个问题似乎与一个类似的问题有关：Merging cursors during onLoadFinished() causes StaleDataException after rotation 但它涉及合并游标并建议使用 swapCursor，我不确定我将如何将其应用于这种情况。

我的想法是 getListView().getItemAtPosition(n) 必须返回对游标的引用而不是新游标，因此当 activity 处于后台并尝试在保存片段时访问现在关闭的游标声明它崩溃了。如前所述，它只会在滚动列表视图时崩溃，我不确定为什么会影响它。

如何在不导致崩溃的情况下正确关闭光标？

编辑代码以响应要求查看光标加载方式的评论：

String[] desired_columns = { 
                MediaStore.Audio.Media._ID,  //this column is needed, even though it won't be displayed so the cursor can populate the listview
                MediaStore.Audio.Media.ARTIST,
                MediaStore.Audio.Media.ALBUM,
                MediaStore.Audio.Media.TITLE,
                MediaStore.Audio.Media.DURATION

                };

        String selectionStatement = MediaStore.Audio.Media.IS_MUSIC + " != ? AND " + MediaStore.Audio.Media.DURATION + " > ?";

        String[] selectionArguments = new String[2];
        selectionArguments[0] = "0";
        selectionArguments[1] = "7000";

        Cursor myCursor = getActivity().getContentResolver().query( MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, 
                                                                    desired_columns, 
                                                                    selectionStatement,     //selection criteria
                                                                    selectionArguments,     //selection arguments like with SQL PDO use ? in criteria and put user input here  to avoid sql injection
                                                                    MediaStore.Audio.AudioColumns.ARTIST + " ASC"); //sort order of results
        //moveToFirst() returns false if the cursor is empty
        if (myCursor != null && myCursor.moveToFirst()) {
            customCursorAdapter myCursorAdapter = new customCursorAdapter(getActivity(), myCursor, 0);

            setListAdapter(myCursorAdapter);

            getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
            getListView().setSelector(R.drawable.list_selection_colouring);
        }

Answer 1

试试这个

        Cursor cursor = null;
        try {
            cursor = (Cursor) getListView().getItemAtPosition(n);
            //do something

        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }

Answer 2

我找到了一个解决方案，它避免了已弃用的 manageQuery 并且也不使用 CursorLoaders。

解决方案是在 onDestroy() 中关闭游标。我尝试在 onPause 内关闭它，但这没有帮助。查看片段生命周期 http://developer.android.com/guide/components/fragments.html#Lifecycle onDestroy 几乎是最后调用的方法，因此片段状态已经保存，可以安全地关闭游标。

这是我使用的代码：

@Override
public void onDestroy() {
   super.onDestroy();
   if (cursor != null) {
      cursor.close();
   }
}

使用 CursorAdapter 关闭 Cursor 会导致后台片段出现 StaleDataException

Closing Cursor causes StaleDataException on backgrounding fragment with CursorAdapter

android

staledataexception

android-fragments

android-cursor

android-cursoradapter