Question

App.config文件配置1

Option Explicit

Dim K1 As Double
Dim K2 As Double
Dim K3 As Double
Dim K4 As Double

Dim y As Double
Dim x As Double
Dim dx As Double
Dim x0 As Integer
Dim y0 As Integer



Function f(x, y) As Double
   f = 0.5 * x - 0.5 * y
    End Function


Sub RK(x, y, dx)

Dim i As Integer
Dim ynew As Double
dx = 0.5
x0 = 0
y0 = 1
K1 = dx * f(x, y)
K2 = dx * f(x + dx / 2, y + K1 / 2)
K3 = dx * f(x + dx / 2, y + K2 / 2)
K4 = dx * f(x + dx, y + K3)
 RK = y + ((K1 + 2 * (K2 + K3 + K4)) / 6)


For i = 0 To 6
ynew = RK(x, y, dx)
x = x + dx
y = ynew
Next i

For j = 1 To 6
Call RK(x, y, dx, ynew)
ActiveCell.Offset(i - 1, 1).Value = x
ActiveCell.Offset(i - 1, 2).Value = y
x = x + dx
y = ynew
Next

End Sub

App.config文件配置2

        <?xml version="1.0" encoding="utf-8" ?>
        <configuration>
          <connectionStrings>
            <add name="MyDBConnectionString" connectionString="Data Source=223.29.207.133;
                 Initial Catalog=MBV5DBLive;User ID=smsuser;Password=sms;IntegratedSecurity=true"
                 providerName="System.Data.SqlClient" />
          </connectionStrings>
        </configuration>

即使我调试配置管理器代码将跳转到catch块，它将显示“对象引用未设置为对象的实例”。以上两个配置文件有什么问题？

Answer 1

您的连接字符串名称似乎为c_str而非MyDBConnectionString。

由于您的网络配置中没有任何 MyDBConnectionString，因此ConfigurationManager.ConnectionStrings["MyDBConnectionString"]会返回null，这就是您获得NullReferenceException的原因当您尝试访问ConnectionString引用的null属性时。

如果除此之外的一切都很好，这应该有用;

var constring = ConfigurationManager.ConnectionStrings["c_str"].ConnectionString;
using (var con = new SqlConnection(constring))
{
}

使用c＃无法访问app.config中的连接字符串

1 个答案: