在从中访问数据之前,请确保正确初始化Cursor

Question

我试图从我的数据库中获取数据.

这是我的代码:

String[] columns = new String[] {COLUMN_FACEBOOK_ALBUM_COVER, COLUMN_FACEBOOK_ALBUM_IS_ACTIVE};

        String whereClause = COLUMN_FACEBOOK_ALBUM_IS_ACTIVE + "= '" + 1 + "'";

        Cursor cAlbum = ourDatabase.query(TABLE_FACEBOOK, columns, whereClause,null, null, null, null);

        columns = new String[] {COLUMN_FACEBOOK_BIG_IMAGE, COLUMN_FACEBOOK_IMAGE_IS_ACTIVE};

        whereClause = COLUMN_FACEBOOK_IMAGE_IS_ACTIVE + "= '" + 1 + "'";

        Cursor cImage = ourDatabase.query(TABLE_FACEBOOK_IMAGES, columns, null,null, null, null, null);

        String[] list = new String[cAlbum.getCount()+cImage.getCount()];

        int p = 0;

        if(cAlbum.getCount() < 1 && cImage.getCount() < 1)
        {
            cAlbum.close();
            cImage.close();
            return null;
        }

        Log.i("cImage length", cImage.getCount()+"");
        Log.i("cAlbum length", cAlbum.getCount()+"");

        Log.i("list length", list.length+"");

        int i = cImage.getColumnIndex(COLUMN_FACEBOOK_BIG_IMAGE);
        int j = cAlbum.getColumnIndex(COLUMN_FACEBOOK_ALBUM_COVER);

        for (cAlbum.moveToFirst(); !cAlbum.isAfterLast(); cAlbum.moveToNext())
        {
            list[p] = cAlbum.getString(j);
            p++;
        }

        for (cImage.moveToFirst(); !cImage.isAfterLast(); cImage.moveToNext())
        {
            list[p] = cImage.getString(i);
            Log.i("image length", list[p].length()+"");
            p++;
        }

        cAlbum.close();
        cImage.close();

        return list;

代码在此行上失败:

list[p] = cImage.getString(i);

错误消息是:

11-27 12:34:59.683: E/CursorWindow(6901): Failed to read row 2, column 0 from a CursorWindow which has 2 rows, 2 columns.
11-27 12:34:59.683: D/AndroidRuntime(6901): Shutting down VM
11-27 12:34:59.683: W/dalvikvm(6901): threadid=1: thread exiting with uncaught exception (group=0x41e9b930)
11-27 12:34:59.693: E/AndroidRuntime(6901): FATAL EXCEPTION: main
11-27 12:34:59.693: E/AndroidRuntime(6901): java.lang.RuntimeException: Unable to create service com.example.imageswidget.WidgetService: java.lang.IllegalStateException: Couldn't read row 2, col 0 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2667)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.app.ActivityThread.access$1600(ActivityThread.java:153)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1329)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.os.Looper.loop(Looper.java:137)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.app.ActivityThread.main(ActivityThread.java:5227)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at java.lang.reflect.Method.invokeNative(Native Method)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at java.lang.reflect.Method.invoke(Method.java:511)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at dalvik.system.NativeStart.main(Native Method)
11-27 12:34:59.693: E/AndroidRuntime(6901): Caused by: java.lang.IllegalStateException: Couldn't read row 2, col 0 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.database.CursorWindow.nativeGetString(Native Method)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.database.CursorWindow.getString(CursorWindow.java:434)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at com.example.imageswidget.DataBaseMain.getFacebookImagesForWidget(DataBaseMain.java:943)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at com.example.imageswidget.WidgetService.onCreate(WidgetService.java:51)
11-27 12:34:59.693: E/AndroidRuntime(6901):     at android.app.ActivityThread.handleCreateService(ActivityThread.java:2657)
11-27 12:34:59.693: E/AndroidRuntime(6901):     ... 10 more

对于通话记录

Log.i("image length", list[p].length()+"");

在代码中断之前,我接到几个电话.这个问题似乎只发生在某些行上,但错误代码并没有告诉我问题是什么.

谢谢你的帮助.

Answer 1

在我的情况下,这是因为我没有在传递到CursorLoader构造函数的投影中包含列.这意味着我试图从返回的游标中不存在的列访问数据.

我希望这有助于某人......

Answer 2

我以前遇到过同样的例外.在我的情况下,原因是包含太多数据的数据库单元格(一个巨大的字符串).从代码判断(COLUMN_FACEBOOK_BIG_IMAGE)我猜你遇到了同样的问题.解决方法是检查放入DB的字符串的大小(并在需要时向下缩放图像).希望这可以帮助!

Answer 3

也许您正在使用旧的数据库。如果您更改了数据库上的某些表、字段，并且现在正在另一台设备上尝试（即您在数据库更改之前已经安装了应用程序），则应该只删除旧数据库并创建新文件。