錯誤：字段初始不能引用非靜態字段，方法或屬性

Question

我找不到任何解決方案張貼問題：

class ApiData 

{ SqlCeConnection conn = new SqlCeConnection(@"Data Source=C:\Users\Peter\Documents \db.sdf;"); 

SqlCeCommand cmd = null; 
    SqlCeDataReader rdr = null; 
    public string code() 
    { 
     conn.Open(); 
     cmd = conn.CreateCommand(); 
     cmd.CommandText ="SELECT code FROM Charakter WHERE id=1"; 
     rdr = cmd.ExecuteReader(); 
     rdr.Read(); 
     string selected = rdr.GetString(0); 
     conn.Close(); 
     return (selected); 
    } 
class Data{ 
    ApiData g= new ApiData(); 
    string vode = **g.code();** 
} 

這是爲什麼收到錯誤「A字段初始不能引用非靜態字段，方法或屬性「在粗體標記行？

Answer 1

嘗試使現場static這是給這個問題

//INITIALLY this field was non-static 
//public string ConnectionString = "Data Source=ServerName;Initial Catalog=DBname;User Id=user_id;Password=password"; 

//Make this field static 
public static string ConnectionString = "Data Source=ServerName;Initial Catalog=DBname;User Id=user_id;Password=password"; 
static SqlConnection sqlConnection = new SqlConnection(ConnectionString); 

希望這有助於...

Answer 2

字段的初始值需要使用常量，靜態字段/方法/屬性或新實例。相反，在構造函數設置：

class Data 
{ 
    ApiData g; 
    string vode; 

    public Data() 
    { 
     g = new ApiData(); 
     vode = g.code(); 
    } 
}