VB.net ConnectionStrings object reference

问题

when connecting i get an error: object reference not set to instance of an object

Form1

Dim c As String = System.Configuration.ConfigurationManager.ConnectionStrings("CON").ConnectionString
Dim con As New MySqlConnection(c)

App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
      <add name="CON" providerName="MySql.Data.MySqlClient" connectionString="Server=localhost;Database=DATABASE_;Uid=user;Pwd=pass" />
    </connectionStrings>
</configuration>

I have no idea how to fix this issue...

This works

Dim con As New MySqlConnection("Server=localhost;Database=DATABASE_;Uid=user;Pwd=pass")

Ultimately i am trying to protect my connection string.

Debug output: A first chance exception of type 'System.NullReferenceException' occurred in Loader.exe This is saying that System.Configuration.ConfigurationManager.ConnectionStrings("CON").ConnectionString is returning null

回答1:

You've differents names in app.config and code.

Imports System.Configuration.ConfigurationManager
Dim cs As String = ConnectionStrings("CON").ConnectionString

EDIT

The problem was a bad app.config setup file. Please read the comments.

来源：https://stackoverflow.com/questions/28653305/vb-net-connectionstrings-object-reference