Question

Is there a way to do reflection pre-compile – at design time?

My intent is to use T4 to spit out custom codes based on classes that implement certain interfaces. I know I can call upon reflection, but I want the T4 script to spit out the additional code before compile, otherwise I will need to compile the code twice, once to generate dlls, twice to let T4 reflect on the previously generated dll and add additional scaffolding.

Is there a way to do reflection at design time?

Is there a better way to do this?

Answer 1

There actually is a way of generating code pre-build based on the CodeModel provided by Visual Studio Automation: The Project Interface provides a Property “CodeModel” that contains a graph of all model artifacts in that project. You might want to traverse it in order to find classes, interfaces, properties, … based on which you generate your output code.

dandrejw already mentioned the Tangible T4-Editor. It has got a free template gallery. There is a reusable template “tangible Visual Studio Automation Helper” which should be extremely helpful in your case. Using this template you could solve your issue like this:

This is code within a t4 template detecting all classes that implement INotifyPropertyChanged.

<#
    // get a reference to the project of this t4 template
    var project = VisualStudioHelper.CurrentProject;
    // get all class items from the code model
    var allClasses = VisualStudioHelper.GetAllCodeElementsOfType(project.CodeModel.CodeElements, EnvDTE.vsCMElement.vsCMElementClass, false);

    // iterate all classes
    foreach(EnvDTE.CodeClass codeClass in allClasses)
    {
        // get all interfaces implemented by this class
        var allInterfaces = VisualStudioHelper.GetAllCodeElementsOfType(codeClass.ImplementedInterfaces, EnvDTE.vsCMElement.vsCMElementInterface, true);
        if (allInterfaces.OfType<EnvDTE.CodeInterface>()
                         .Any(i => i.Name == "INotifyPropertyChanged"))
        {
            #>Render your code here<#
        }
    }
#>

Put your output code where the code snippet says “Render your code here”.