Visual Studio 2010 introduced a much-anticipated feature, Web configuration transformations. This feature allows to configure a web application project to transform the web.config file during deployment based on the current build configuration (Debug, Release, etc).

If you haven’t already tried it there is a nice step-by-step introduction post to XML transformations on the Visual Web Developer Team Blog and for a quick reference on the supported syntax you have this MSDN entry.

Unfortunately there are some bad news, this new feature is specific to web application projects since it resides in the Web Publishing Pipeline (WPP) and therefore is not officially supported in other project types like such as a Windows applications. The keyword here is officially because Vishal Joshi has a nice blog post on how to extend it’s support to app.config transformations.

However, the proposed workaround requires that the build action for the app.config file be changed to Content instead of the default None. Also from the comments to the said post it also seems that the workaround will not work for a ClickOnce deployment.

Working around this I tried to remove the build action change requirement and at the same time add ClickOnce support. This effort resulted in a single MSBuild project file (AppConfig.Transformation.targets) available for download from GitHub. It integrates itself in the build process so in order to add app.config transformation support to an existing Windows Application Project you just need to import this targets file after all the other import directives that already exist in the *.csproj file.

Before – Without App.config transformation support

  ...
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
  <Target Name="BeforeBuild">
  </Target>
  <Target Name="AfterBuild">
  </Target>
</Project>

After – With App.config transformation support

  ...
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
  <Import Project="C:\MyExtensions\AppConfig.Transformation.targets" />
  <Target Name="BeforeBuild">
  </Target>
  <Target Name="AfterBuild">
  </Target>
</Project>

As a final disclaimer, the testing time was limited so any problem that you find let me know. The MSBuild project invokes the mage tool so the Framework SDK must be installed.

I finally had some spare time and was able to check the problem reported by Geoff Smith and believe the problem is solved. The Publish command inside Visual Studio triggers a build workflow different than through MSBuild command line and this was causing problems. I posted a new version in GitHub that should now support ClickOnce deployment with app.config tranformation from within Visual Studio and MSBuild command line. Also here is a link for the sample application used to test the new version using the Publish command with the install location set to be from a CD-ROM or DVD-ROM and selected that the application will not check for updates.

Thanks to Geoff for spotting the problem.