Object reference not set to an instance of an object. With a static class? ! Configurationmanager

Question

1.00/5 (1 vote)

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C#

public string connectionString = ConfigurationManager.ConnectionStrings["HPDL160G62"].ConnectionString;

throws me

C#

Object reference not set to an instance of an object.

error.

thanks

EDIT MY APP.CONFIG

XML

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="HPDL160G62" providerName="System.Data.SqlClient" connectionString="Data Source=HPDL160G62;Initial Catalog=Database;User ID=username;Password=password;"/>
  </connectionStrings>
  <appSettings>
    
  </appSettings>
<startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/></startup></configuration>

This is in a Class Library and I'm executing from cl app.

What I have tried:

added static keyword and removed but just I don't get why do I get this error with a static class ?!
placed just the top of the class and tried placing into methods but always the same

Posted 20-Jun-16 0:43am

Zsolt Madlen

Updated 20-Jun-16 1:14am

v4

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CHill60 20-Jun-16 7:08am

You've mentioned this is a class library being executed from an application - is this the application config or the DLL config ... ConfigurationManager will only read the settings for the currently running assembly ... i.e. the application

Zsolt Madlen 20-Jun-16 7:23am

This comment is the Real solution for my problem! Thanks

CHill60 20-Jun-16 7:25am

I'll update my solution in case anyone else has a similar problem

CHill60 20-Jun-16 7:30am

By the way - you can have an app.config for the DLL - I've included a link in my update that shows how to use one.

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CHill60 · Accepted Answer · 2016-06-20T00:49:00

It will become more obvious what is happening if you break that line down into segments

C#

var x = ConfigurationManager.ConnectionStrings;
var y = x["HPDL160G62"];
var z = y.ConnectionString;

x will not be a problem because, as you say, it's a static class so you don't need an instance.

But y is null because there is nothing in the collection that matches "HPDL160G62".

Therefore you get the error when assigning to z

[EDIT]
The reason that there was no matching item in the collection is because the App.Config belonged to a DLL. ConfigurationManager only reads the app.config for the currently running assembly i.e. the application calling the DLL.

So the solution is to have this connection string in the App.Config for the calling application
OR
You can still have a DLL config but you will have to read it manually (I found a good example of how to do this here[^])