無法創建連接字符串

Question

我正在開發一個網站，我無法創建連接字符串，我已經包含了所有必需的命名空間，但是當我創建一個字符串變量來存儲連接時，它不會來聲明SqlConnection對象，但我可以在構造函數類中創建連接字符串，爲什麼我無法在構造函數之外創建連接。有沒有什麼具體的理由..

Answer 1

的App.config：

<?xml version="1.0" encoding="utf-8" ?> 
<configuration> 
    <connectionStrings> 
    <add name="main" providerName="System.Data.SqlClient" connectionString="Data  Source=localhost;Initial Catalog=mydatabase;User Id=myid;Password=mypassword;"/> 
    </connectionStrings> 
<configuration> 

C＃代碼：

using System.Configuration; 

public string _connectionString = ConfigurationManager.ConnectionStrings[1].ConnectionString; 

public string GetString(string sql, SqlParameter[] parameters) 
{ 
    List<string> result = new List<string>(); 
    SqlDataReader reader; 
    using (SqlConnection connection = new SqlConnection(_connectionString)) 
    { 
    SqlCommand command = new SqlCommand(sql, connection); 
    if (parameters != null) 
    { 
     command.Parameters.Clear(); 
     command.Parameters.AddRange(parameters); 
    } 
    connection.Open(); 
    reader = command.ExecuteReader(); 
    while (reader.Read()) 
    { 
     string row = string.Empty; 
     foreach (string col in reader) 
     { 
     row += col + ","; 
     } 
     result.Add(row) 
    } 
    reader.Close(); 
    } 
    return result; 
}