ConnectionStringSettings NullReference错误

Question

我在web.config中有以下设置，作为配置元素的子项：

<connectionStrings>
  <clear />
  <add name="GingerlimeDB"
       connectionString="Data Source=localhost;
                       Integrated Security=False;
                       Initial Catalog=dbname;
                       User Id=accountname;
                       Password=password;"
       providerName="System.Data.SqlClient" />
</connectionStrings>

在我希望检索连接字符串的代码中，我放置了：

using System.Configuration
...
    var connStringObject = ConfigurationManager.ConnectionStrings["GingerlimeDB"];
    string connectionString = connStringObject.ConnectionString;
    Console.WriteLine(connectionString);

我没有进入控制台输出，而是显示：

  

对象引用未设置为对象的实例。

如何从Web配置中获取连接字符串？

Answer 1

假设您的web.config文件如下所示：

<?xml version="1.0"?>
<configuration>
    <connectionStrings>
        <clear />
        <add name="GingerlimeDB"
                   connectionString="Data Source=localhost;
                   Integrated Security=False;
                   Initial Catalog=dbname;
                   User Id=accountname;
                   Password=password;"
                   providerName="System.Data.SqlClient" />
    </connectionStrings>
</configuration>

我使用几乎相同的东西：

using System.Configuration;
....
internal bool OpenDatabaseConnection()
{
        try
        {
            string connectionString = ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString;
            dbConnection = new SqlCeConnection(connectionString);
            dbConnection.Open();
            return true;
        }
        catch (SqlCeException ex)
        {
            this.errorLogging = new ErrorLogging(ex.Message, ex.Source, ex.HelpLink, ex.GetType().ToString());
        }
        catch (InvalidOperationException ex)
        {
            this.errorLogging = new ErrorLogging(ex.Message, ex.Source, ex.HelpLink, ex.GetType().ToString());
        }
        catch (ArgumentException ex)
        {
            this.errorLogging = new ErrorLogging(ex.Message, ex.Source, ex.HelpLink, ex.GetType().ToString());
        }
        catch (ConfigurationErrorsException ex)
        {
            this.errorLogging = new ErrorLogging(ex.Message, ex.Source, ex.HelpLink, ex.GetType().ToString());
        }
        return false;
}

哪一行实际导致NullReference异常？ （对象未设置为对象的实例）？