Question

这是我的问题的后续跟进： How to close a cursor used in a for loop

响应解决了“Cursor finalized而没有事先关闭”的警告，但它在非常特殊的情况下导致了StaleDataException。

如果列表已滚动，则此光标关闭......

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

并且片段背景我得到以下错误：

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$1.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)

此问题似乎与类似问题有关：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的游标，因此当活动背景并尝试访问现在关闭的游标同时保存片段状态时它会崩溃。如前所述，如果列表视图已滚动，它只会崩溃，我不确定为什么会影响它。

如何正确关闭光标而不会导致崩溃？

编辑代码以响应要求查看光标加载方式的注释：

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

我找到了一个解决方案，它避免了弃用的manageQuery，也没有使用CursorLoaders。

解决方案是在onDestroy（）中关闭光标。我尝试在onPause中关闭它，但这没有帮助。查看片段生命周期http://developer.android.com/guide/components/fragments.html#Lifecycle onDestroy几乎是最后一个被调用的方法，因此片段状态已经被保存，从而可以安全地关闭光标。

以下是我使用的代码：

<form action="#{request.contextPath}/download/#{bean.fileName}">
    <input type="hidden" name="selectedDownloadValue" value="foo" />
    <input type="submit" value="Download" />
</form>

Answer 2

试试这个

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

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

关闭Cursor会导致使用CursorAdapter对背景片段进行StaleDataException

2 个答案: