Question

我在C＃中有一个带有数据库的方法。现在，我尝试返回该值，但是由于该字符串是在while循环中创建的，因此表明该字符串不存在。是否可以返回在while读取循环中创建的字符串kampioen及其值？

public string getkampioen(string selecteditem)
{
    using (MySqlConnection connection = new MySqlConnection(connectionString))
    {
        connection.Open();
        string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
        MySqlCommand cmd = new MySqlCommand(query, connection);
        MySqlDataReader Reader = cmd.ExecuteReader();
        while (Reader.Read())
        {
           string kampioen = (string)Reader["aantalkampioenschappen"].ToString();
        }
        return kampioen; 
    }
}

Answer 1

只需将声明移出循环：

public string getkampioen(string selecteditem)
{
    string kampioen; //declare here
    using (MySqlConnection connection = new MySqlConnection(connectionString))
    {
        connection.Open();
        string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
        MySqlCommand cmd = new MySqlCommand(query, connection);
        MySqlDataReader Reader = cmd.ExecuteReader();
        while (Reader.Read())
        {
           kampioen = (string)Reader["aantalkampioenschappen"].ToString();
        }
        return kampioen; 
    }
}

Answer 2

您可以在while循环之前声明字符串。

public string getkampioen(string selecteditem)
{
    using (MySqlConnection connection = new MySqlConnection(connectionString))
    {
        connection.Open();
        string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
        MySqlCommand cmd = new MySqlCommand(query, connection);
        MySqlDataReader Reader = cmd.ExecuteReader();
        string kampioen = "";
        while (Reader.Read())
        {
           kampioen = (string)Reader["aantalkampioenschappen"].ToString();
        }
        return kampioen; 
    }
}

Answer 3

正如其他人所说，将public class MainActivity extends AppCompatActivity { ListView list; ArrayList<Flick> flicks; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); list = findViewById(R.id.list); flicks = new ArrayList<>(); flicks.add(new Flick("Wizard of Oz", "Metro-Goldwyn-Mayer", "VARIOUS","1939", "", 98)); ... flicks.add(new Flick("Jaws", "Universal", "Steven Spielberg", "1975", "", 97)); CustomAdapter customAdapter = new CustomAdapter(this, R.layout.custom_layout, flicks); listt.setAdapter(customAdapter); } ... }移到循环之外。而且，如果您要获取一个特定值而不是一个随机值（如果返回了多个记录），则可能需要连接字符串或将结果限制为第一行，如下所示：

kampioen

在while循环中返回

3 个答案: