Question

我正在开发一个应用程序的电子学习类型，我从列表中的数据库中检索数据。

它在模拟器上工作正常，但是当我在真实设备上使用该应用程序的APK文件时，它不会在列表中显示任何数据，我的数据库存储在windows-file explorer-package-data-database- TABLE_NAME。

我指的是这个网站

http://anujarosha.wordpress.com/2011/12/19/how-to-retrieve-data-from-a-sqlite-database-in-android/

以下是使用数据库

的代码片段

list_adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, namelist1());

        list1.setAdapter(list_adapter);

    }

    public  List<String> namelist1()
    {
        // We have to return a List which contains only String values. Lets create a List first
        List<String> namelist= new ArrayList<String>();

        // First we need to make contact with the database we have created using the DbHelper class

        Database_helper_class open_database_helper= new Database_helper_class(this);
        // Then we need to get a readable database
        SQLiteDatabase sqlitedatabase = open_database_helper.getReadableDatabase();
        // We need a a guy to read the database query. Cursor interface will do it for us
        //(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
        Cursor cursor =sqlitedatabase.query(open_database_helper.TABLE_E_LEARNING,null,null,null,null,null,null);
        //above query is read all the database column

        // Cursor object read all the fields. So we make sure to check it will not miss any by looping through a while loop

        while(cursor.moveToNext()){
            String str_name = cursor.getString(cursor.getColumnIndex(Database_helper_class.QUES_COLUMN));
            String str_id = cursor.getString(cursor.getColumnIndex(Database_helper_class.ANS_COLUMN));
            //double str_gpa = cursor.getDouble(cursor.getColumnIndex(Database_helper_class.GPA_COLUMN));


            // Finish reading one raw, now we have to pass them to the POJO
            nameclass nameclassobj1=new nameclass();
            nameclassobj1.setname(str_name);
            nameclassobj1.setid(str_id);
            //nameclassobj1.setgpa(str_gpa);

            // Lets pass that POJO to our ArrayList which contains undergraduates as type
              pojo_namelist.add(nameclassobj1);

            // But we need a List of String to display in the ListView also.
                //That is why we create "nameList"
            namelist.add(str_name);

        }
        sqlitedatabase.close();

Answer 1

sqlitedatabase.query()返回位于第一条记录之前的光标。在尝试访问任何数据之前，请务必致电moveToFirst()。

Answer 2

在DBHelper.class中验证您的数据库路径。然后在调用while循环之前写下面的行。

cursor.moveToFirst();

这将指向您的第一条记录，然后您的while循环将起作用。

Answer 3

试试这样：

// Cursor object read all the fields. So we make sure to check it will not miss any by looping through a while loop
cursor.moveToFirst();
    while(!cursor.isAfterLast()){
        String str_name = cursor.getString(cursor.getColumnIndex(Database_helper_class.QUES_COLUMN));
        String str_id = cursor.getString(cursor.getColumnIndex(Database_helper_class.ANS_COLUMN));
        //double str_gpa = cursor.getDouble(cursor.getColumnIndex(Database_helper_class.GPA_COLUMN));


        // Finish reading one raw, now we have to pass them to the POJO
        nameclass nameclassobj1=new nameclass();
        nameclassobj1.setname(str_name);
        nameclassobj1.setid(str_id);
        //nameclassobj1.setgpa(str_gpa);

        // Lets pass that POJO to our ArrayList which contains undergraduates as type
          pojo_namelist.add(nameclassobj1);

        // But we need a List of String to display in the ListView also.
            //That is why we create "nameList"
        namelist.add(str_name);

    }

如果到达光标的末尾，请使用isAfterLast（）方法检查。

Answer 4

很抱歉迟到的回复，忙于其他申请

实际上数据没有保存在数据库中，这就是为什么我没有在设备上获取它。它现在有效。

在真实设备上运行时，无法从数据库中检索数据

4 个答案: