Visual Studio: differentiate app.config for debug and release mode

Is there a way to automatically use a separate app.config when building in release mode?

In other words, I want to test with one app.config, and release with another.

Currently, I keep a separate copy called app.config.production, and manually overwrite bin\Release\Application.exe.config after building for release.

Unload the project in Solution Explorer via the context menu.

Edit the .csproj file via the context menu and add this:

<PropertyGroup>
    <AppConfig>App.$(Configuration).config</AppConfig>
</PropertyGroup>

I have recently posted a supremely belated response to a similar SO topic: https://stackoverflow.com/a/27546685/2798367

I will repeat it here for clarity:

This is somewhat late to the party, but I stumbled upon a nice way of implementing the web.transform approach for app.config files. (i.e. it makes use of the namespace http://schemas.microsoft.com/XML-Document-Transform)

I think it is "nice" because it is a pure xml approach and doesn't require 3rd party software.

A parent / default App.config file is descended from, according to your various build configurations. These descendants then only override what they need to. In my opinion this is much more sophisticated and robust than having to maintain x number of config files which get copied in their entirety, such as in other answers.

A walkthrough has been posted here: http://mitasoft.wordpress.com/2011/09/28/multipleappconfig/

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Look, Mom - No explicit post-build events in my IDE!

A simple and fast way is to create a second file "App.release.config" and insert this pre-build event:

IF $(ConfigurationName) == Release COPY /Y "$(ProjectDir)App.config" "$(ProjectDir)App.debug.config"
IF $(ConfigurationName) == Release COPY /Y "$(ProjectDir)App.release.config" "$(ProjectDir)App.config"

And this post build event:

IF $(ConfigurationName) == Release COPY /Y "$(ProjectDir)App.debug.config" "$(ProjectDir)App.config"

This might be a bit odd, but it will allow you to keep using the .Settings files as debug settings, that are still linked to the App.config. The App.release.config must be build by hand, but it's pretty easy to switch this functionality.

I highly recommend SlowCheetah for app.config transformations. Visit this nuget gem here Visual Studio Gallery

Similar to top answer but with this approach you can see the actual file if preferred and intellisense doesn't complain in csproj file:

  <Target Name="SetAppConfig" BeforeTargets="Compile">
    <Copy SourceFiles="debug.config" DestinationFiles="app.config" OverwriteReadOnlyFiles="true" Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' " />
    <Copy SourceFiles="release.config" DestinationFiles="app.config" OverwriteReadOnlyFiles="true" Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' " />
  </Target>

A clean solution is to group 2 files App.Debug.config and App.Release.config into App.config and change the good file into App.config depending on the configuration at compile time:

<ItemGroup>
    <None Include="App.config" />
    <None Include="App.Debug.config">
        <DependentUpon>App.config</DependentUpon>
    </None>
    <None Include="App.Release.config">
        <DependentUpon>App.config</DependentUpon>
    </None>
</ItemGroup>
<Target Name="SetAppConfig" BeforeTargets="Compile">
    <Copy SourceFiles="App.Debug.config" DestinationFiles="App.config" OverwriteReadOnlyFiles="true" Condition=" '$(Configuration)' == 'Debug' " />
    <Copy SourceFiles="App.Release.config" DestinationFiles="App.config" OverwriteReadOnlyFiles="true" Condition=" '$(Configuration)' == 'Release' " />
</Target>

With this solution you will get something like this in Visual Studio:

I don't know if this helps, but app.config will recognise the standard MSBUILD substitution strings such as $(Configuration).