c# - Can we share some contents of App.config between projects?

Question

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?

Answer 1

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:

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)!