T4: using properties in both Visual Studio and MSBuild

Question

I am having trouble creating a T4 template that can be used to generate a relatively simple C# code both from Visual Studio and from MSBUild. The template references a DLL, which resides in the output path of the project. Apart from that, it is a fairly simple template that loops through a collection of domain objects and outputs a test method for each of them.

MSDN suggests the following approach for using properties in both hosts:

<!-- Define a project property, myLibFolder: -->
<PropertyGroup>
    <myLibFolder>$(MSBuildProjectDirectory)\..\libs</myLibFolder>
</PropertyGroup>

<!-- Tell the MSBuild T4 task to make the property available: -->
<ItemGroup>
    <T4ParameterValues Include="myLibFolder">
      <Value>$(myLibFolder)</Value>
    </T4ParameterValues>
  </ItemGroup>

Unfortunately, this just does not work. When executing via MSBuild, I get the following error:

Compiling transformation: Metadata file '$(myLibFolder)Cmc.SpeedWays.Core.Testing.dll' could not be found   

Did anybody manage to solve this problem or at least find an acceptable workaround? We are using VS2012 and MSBUild 4.0.

Answer 1

I had the same problem and am sorry to say that I did not get a single obvious fix. However the problem did go away, it seems like a collection of possible issues.

I think the key one was this type of property declaration only works if you build the solution/project with MSBuild, if you use Visual Studio the properties will be null. I think this was the confusion for me. In the end I ended up with calls in my template, where I try to get the MSbuild declared property, and if this fails as VS

var configName = Host.ResolveParameterValue("-", "-", "configuration");
if (String.IsNullOrEmpty(configName)==true)
{
    WriteLine ("// Generated from Visual Studio");
    IServiceProvider serviceProvider = (IServiceProvider)this.Host;
    DTE dte = serviceProvider.GetService(typeof(DTE)) as DTE;  
    configName = dte.Solution.SolutionBuild.ActiveConfiguration.Name ;
}

Other thing to watch out for is building invalid strings with string concatenation, easy to end up with a null