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I have two independent projects in my Visual Studio 2008 solution. Both has its own App.config. But in one project, I need one or two properties defined in another project's App.config. Is it possible to share part of the App.config contents from other project?

CharithJ
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5YrsLaterDBA
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5 Answers5

35

Yes - of course. Any configuration section can be "externalized" - e.g.:

<appSettings configSource="AppSettings.DEV.config" />
<connectionStrings configSource="MyConnection.config" />

or

<system.net>
   <mailSettings>
      <smtp configSource="smtp.TEST.config" />

vs. 

<system.net>
   <mailSettings>
      <smtp configSource="smtp.PROD.config" />

Any configuration section can be put into a separate file that can be shared between projects - but no configuration section groups, and unfortunately, it's sometimes a bit tricky to know which is which.

Also, in some cases, Visual Studio will complain (using red wavy underlines) that the "configSource" supposedly isn't valid - but it is - it's defined on the ConfigurationSection object in the .NET config system.

UPDATE:
another feature that hardly enough developers seem to know and use is the ability in Visual Studio to add existing files from a different project as a link:

alt text

With this, you can add links to files into your local project, and they'll always be kept up to date. Great productivity booster if you need to do some file-level sharing (like for common configuration files or such)!

Glorfindel
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marc_s
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  • but the target file, such as "MyConnection.config" in your example, must be in the same directory or subdirectory? – 5YrsLaterDBA Apr 30 '10 at 20:41
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    @5YrsLaterDBA: yes, it has to be in the same directory or a sub-directory thereof. It can be a "linked" file in Visual Studio, however - or a hard link on disk (NTFS link - a "pointer" to another file that looks and acts like "The Real Thing") – marc_s Apr 30 '10 at 20:57
  • Hmmm... I wish I had though of mentioning linking. lol. but you left out something important, marc. – Sky Sanders May 01 '10 at 02:52
  • OK, I added it as a link, now how do I access the various values of the linked app config from the second project? – nawfal Jun 07 '12 at 12:54
  • I'd like to know how to do as nawfal described as well. – Justin May 08 '13 at 14:50
  • @Justin: just as normal in .NET - just use the [ConfigurationManager class](http://msdn.microsoft.com/en-us/library/system.configuration.configurationmanager.aspx) ... – marc_s May 08 '13 at 15:56
3

Try this:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings file="PROD.config">
    <add key="common.Currency" value="GBP" />
  </appSettings>
</configuration>
Damian Powell
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  • yeah, but the "file=" attribute is only valid on the section - nothing else can be put into external files with that method..... – marc_s Apr 30 '10 at 19:27
1

Only the "running" app.config is used, but you can go external like marc_s says.

You can also create a .Settings file that's "shared". Go to the "shared" project properties, the Settings tab on the left, create a setting with Application scope, and set the Access Modifier on top to Public. In your other project you can then use ClassLibrary1.Properties.Settings.Default.SettingName to access it. It will be strongly typed, but you may need it at compile time.

Nelson Rothermel
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  • But doesn't the Settings code that is generated rely on the app.config of the running up for persistence? Then you would still need a copy of that file for each running app. – ProfK Nov 02 '14 at 05:30
  • @ProfK: Yes, you're right. The .settings files can have default values which end up as `DefaultSettingValueAttribute` in code, unlike regular app settings in app.config. However, any deviation from the default values would end up in each individual app.config. Since the settings are stored in a section in app.config you could use a combination of the two and externalize it with configSource while keeping the compiled defaults and strong typing. I guess it all depends what you're looking for. – Nelson Rothermel Nov 03 '14 at 22:08
1

Something I like to do, especially when trying to coordinate ServiceModel elements between libraries and tests is to use configSource to fragment the config in the target library and simply link/copy always the fragments in my test projects.

That way I only maintain in one location.

You could take it one step farther and simply have a common directory in the solution and link the fragments in all projects.

Sky Sanders
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0

In that situation, I would think using a Database to store some configuration data would be ideal. Each app does its own thing, but they look to a shared database to get those common pieces of information.

EDIT: I spoke too soon! Looks like both the OP and I learned something about config files =D

Tejs
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