Android：IllegalStateException：无法执行此操作，因为连接池已关闭

Question

我一次又一次地收到错误，当我回到previouse页面或启动页面时应用程序崩溃。在使用任何查询之前我初始化这个

dbhelper = new MyDbHelper(this);
dbhelper.onOpen(db);

如果我对db.close的代码行发表评论，或者甚至在游标关闭后使用db.close，则会反复出现错误。有人告诉我如何处理数据库。为什么会出现此错误。  谢谢你的支持  这是我的代码

public void getDoenLoaddata() {
        SQLiteDatabase db = dbhelper.getWritableDatabase();
        Cursor cursor = db.rawQuery("select * from ActivityObjectList", null);

        if (cursor.moveToFirst()) {
            do {
                imageName = cursor.getString(cursor.getColumnIndex("imageaudioPath"));
                String strDownLoadStatus = cursor.getString(cursor.getColumnIndex("DownLoad_Status"));

                if (strDownLoadStatus.equalsIgnoreCase("0")) {
                    if (imageName.endsWith(mp3_Pattern))
                    {

                        str_DownLoadUrl = namespace + "/DownloadFile/FilePathMobile/ATTACHMENT/FileName/" + imageName;
                        DownLoadAudioFile(str_DownLoadUrl, imageName);
                        strDownLoadStatus = "1";
                        dbhelper.update_DownLoadStatus(imageName, strDownLoadStatus);
                    }
                    if (imageName.endsWith(png_Pattern) || imageName.endsWith(jpg_pattern) || imageName.endsWith(bmp_pattern) || imageName.endsWith(gif_pattern) || imageName.endsWith(jpeg_pattern)) {
                        str_DownLoadUrl = namespace + "/DownloadFile/FilePathMobile/ATTACHMENT/FileName/" + imageName;
                        download_PngFile(str_DownLoadUrl, imageName);
                        strDownLoadStatus = "1";
                        dbhelper.update_DownLoadStatus(imageName, strDownLoadStatus);
                    }
                }
            }
            while (cursor.moveToNext());
        }
        cursor.close();
        //db.close();
    }