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DLL with configuration file

, 22 May 2011
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Using configuration files in DLL is not trivial, but is very simple.
Using configuration files in DLL is not trivial.
To accomplish this, we must follow these steps:
  • Add a reference to System.Configuration
  • Add a new Application Configuration File and the name it [Your project].dll.config
  • Change the BuildAction property of the config file to Content
  • Change the Copy to Output property to "Copy Always"
After these steps, you can access the configuration file this way:
//Open the configuration file using the dll location
Configuration myDllConfig = 
// Get the appSettings section
AppSettingsSection myDllConfigAppSettings = 
// return the desired field 
return myDllConfigAppSettings.Settings["MyAppSettingsKey"].Value; 
Your configuration file should look like this:
<?xml version="1.0" encoding="utf-8" ?>
    <add key ="MyAppSettingsKey" value="MyValue"/>
That's all. Hope you enjoy this tip.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author


Brazil Brazil
I'm a Brazilian senior system analyst and team leader and I live in Dublin, Ireland. I've been working with software development since 1996.

Comments and Discussions

QuestionThanks for the straight-to-the-point instructions, it helped me a lot! PinmemberMember 124954625-May-14 5:20 
QuestionNot working when updating config file values Pinmemberxyz from Bangalore20-Oct-13 18:50 
GeneralMy vote of 5 Pinmemberremi22211-Jul-13 7:27 
QuestionNot work in WebApplication [modified] PinmemberMlsoun1-Oct-12 2:04 
AnswerRe: Not work in WebApplication PinmemberFregate19-Feb-13 16:03 
GeneralRe: Not work in WebApplication Pinmemberfmsalmeida20-Feb-13 0:12 
GeneralRe: Not work in WebApplication PinmemberFregate20-Feb-13 12:15 
GeneralRe: Not work in WebApplication Pinmembereng_george128-Jan-14 1:30 
QuestionVS10 Saves Setting to Project.dll.config PinmemberMember 462571327-Mar-12 5:24 
I had an interesting experience trying to implement this in a VB project. I renamed the app.config to P8Library.dll.config and even though it had been renamed, all the settings were still being saved to it. That's a nice feature because I can use VS2010's Settings panel to set all the default application settings and since it's in the standard format, it encrypts easily. I had to change the code to read it since it appears to .Net runtime as a ClientSettingsSection, not as ApplicationSettings.
One other thing when dealing with configuration files and trying to get your settings out of it--if you are using connection strings, they are stored in a seperate part of the app.config. Below is the code I ended up using:
' Load up the Configuration Object and encrypt if necessary
Dim cfg As Configuration = ConfigurationManager.OpenExeConfiguration(My.Application.Info.DirectoryPath & "\P8Library.dll")
Dim AppCfg As ClientSettingsSection = cfg.GetSection("applicationSettings/P8Library.My.MySettings")
For Each st As SettingElement In AppCfg.Settings
Dim value As String = st.Value.ValueXml.InnerText
Dim name As String = st.Name
AppSettings.Add(name, value)
If Not AppCfg.SectionInformation.IsProtected Then
AppCfg.SectionInformation.ForceSave = True
End If

Dim section As ConnectionStringsSection = cfg.GetSection("connectionStrings")
For Each cn As ConnectionStringSettings In section.ConnectionStrings
AppSettings.Add(cn.Name, cn.ConnectionString)
If Not section.SectionInformation.IsProtected Then
section.SectionInformation.ForceSave = True
End If


In the main program I declared a dictionary AppSettings(Of string, string) and used that to get my settings from. I did have to mark the P8Library.dll.config file as Content and include it in the installer as the author noted.
GeneralReason for my vote of 5 This solved a problem that I've been... Pinmemberjtdavies8-Feb-12 8:54 
GeneralReason for my vote of 5 Nice, I like it, and I am bookmarkin... PinmemberFDW3-Nov-11 1:06 
GeneralReason for my vote of 5 It is very good :) PinmemberCaner Korkmaz23-Aug-11 0:14 
GeneralReason for my vote of 5 Bookmarked for future ref. PinmemberKeithAMS2-Jun-11 22:40 
QuestionPossible in .NET 1.1? PinmemberKeithAMS27-Oct-11 23:28 
AnswerRe: Possible in .NET 1.1? Pinmemberfmsalmeida28-Oct-11 3:18 
GeneralGood Tip PinmemberKeithAMS2-Jun-11 22:40 
GeneralRe: Good Tip Pinmemberfmsalmeida3-Jun-11 2:32 
GeneralExplain why.... PinmemberEngleA27-May-11 3:28 
GeneralRe: Explain why.... Pinmemberfmsalmeida27-May-11 4:16 
QuestionToo complex? PinmemberRiz Thon23-May-11 20:03 
AnswerRe: Too complex? Pinmemberfmsalmeida24-May-11 4:10 

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