超载解析失败，因为无法访问“项目”

Question

I don't know why I am getting this error in my custom class

Overload resolution failed because no 'item' is accessible" on line 15 and 16. To see the code follow the link

Imports System.Configuration

Public Class AppSettings 
  Private config As Configuration

  Public Sub AppSetting()
    config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
  End Sub

  Public Function GetConnectionString(ByVal key As String) As String
    Return config.ConnectionStrings.ConnectionStrings(key).ConnectionString
  End Function

  Public Sub SaveConnectionString(ByVal key As String, ByVal value As String)
    config.ConnectionStrings(key).ConnectionString = value
    config.ConnectionStrings(key).ProviderName = "MySql.Data.MySqlClient"
    config.Save(configurationSaveMode.Modified)
  End Sub
End Class

Answer 1

You are missing a .ConnectionStrings between config and .ConnectionStrings(key) as you correctly have in your GetConnectionString method:

config.ConnectionStrings.ConnectionStrings(key).ConnectionString = value
config.ConnectionStrings.ConnectionStrings(key).ProviderName = "MySql.Data.MySqlClient"

But you could use a temporary variable to simplfy

Dim connString = config.ConnectionStrings.ConnectionStrings(key)
connString.ConnectionString = value
connString.ProviderName = "MySql.Data.MySqlClient"

or using a With statement

With config.ConnectionStrings.ConnectionStrings(key)
    .ConnectionString = value
    .ProviderName = "MySql.Data.MySqlClient"
End With