How to force loading of an referenced assembly that is not explicitly used by the project

Question

I have the following scenario:

One host application, that hosts (win)forms that are defined in other projects of the same solution. The hosted forms all implement the same interface. Since the host application references all those other projects dynamic loading (assembly-resolving) is not involved (and not wanted).

Now I thought that I could iterate AppDomain.CurrentDomain.GetAssemblies(), getting all types and filter which of the types implement my interface. But since I never explicitly use the other projects from the host-project the assemblies won't be loaded in the host-app and thereby AppDomain.CurrentDomain.GetAssemblies() won't list them.

I think in most cases this behavior is good, but in my case (reflection usage) it's a problem. Is there a way to force loading (specific) assemblies that are referenced but not explicitly used? I'm looking for visual studio/project-settings way to do this - I don't like the idea to write code to get assemblies loaded that are already referenced :(

Possible solutions:

• Call Assembly.Load for each of the assemblies. con: code-change in the host app
• Call a known class/method from the forms-project(s) to force loading. con: code change in the host app and knowledge of class/method to call

Answer 1

Answer based on the comment from TnTinMn. Thanks for the suggestion!

• Change the static Program class (Entry point of the host app) to be a partial class
• Create a TextTemplate/T4 file named Program.AssemblyLoader.tt
• Add the following content:

Program.AssemblyLoader.tt:

<#@ template language="C#" hostSpecific="true" debug="True" #>
<#@ output extension="cs" #>
<#@ assembly name="System.Core" #>
<#@ assembly name="EnvDte" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Text.RegularExpressions" #>
<#@ import namespace="System" #>
<#

    var visualStudio = (EnvDTE.DTE)(Host as IServiceProvider).GetService(typeof(EnvDTE.DTE));
    var solution = (EnvDTE.Solution)visualStudio.Solution;
    var projects = solution.Projects;

    // Assume that the first item is the main project, the host app.
    // Index is **NOT** zero-based!
    var main = (EnvDTE.Project)projects.Item(1);
    var p = main.Properties.Item("DefaultNamespace");
    var ns = p.Value.ToString();

#>
using System;
using System.Linq;
using System.IO;
using System.Reflection;

namespace <# WriteLine(ns); #>
{
    static partial class Program
    {
        static Program()
        {
            //! Generated file. Do not edit. Check the .tt file instead!
<#
foreach(EnvDTE.Project proj in projects)
{
    if(proj.Properties == null || proj.Properties.Item("OutputFileName") == null)
        continue;

    EnvDTE.Property p2 = proj.Properties.Item("OutputFileName") as EnvDTE.Property;
    WriteLine("            LoadAssemblyIfNecessary(\"" + p2.Value + "\");");
}
#>
        }

        private static readonly AssemblyName[] REFS = Assembly.GetExecutingAssembly().GetReferencedAssemblies();
        private static readonly string APP = Path.GetFileName(System.Windows.Forms.Application.ExecutablePath);

        private static void LoadAssemblyIfNecessary(string name)
        {
            if (string.Equals(name, APP, StringComparison.InvariantCultureIgnoreCase)) return;

            if (!REFS.Any(x => x.Name.StartsWith(Path.GetFileNameWithoutExtension(name), StringComparison.InvariantCultureIgnoreCase)))
            {
                AppDomain.CurrentDomain.Load(Path.GetFileNameWithoutExtension(name));
            }
        }
    }
}

Example for the generated Program.AssemblyLoader.cs:

using System;
using System.Linq;
using System.IO;
using System.Reflection;

namespace Your.Name.Space
{
    static partial class Program
    {
        static Program()
        {
            //! Generated file. Do not edit. Check the .tt file instead!
            LoadAssemblyIfNecessary("HostApp.dll");
            LoadAssemblyIfNecessary("Dependency1.dll");
            LoadAssemblyIfNecessary("Dependency2.dll");
            LoadAssemblyIfNecessary("Modul1.exe");
        }

        private static readonly AssemblyName[] REFS = Assembly.GetExecutingAssembly().GetReferencedAssemblies();
        private static readonly string APP = Path.GetFileName(System.Windows.Forms.Application.ExecutablePath);

        private static void LoadAssemblyIfNecessary(string name)
        {
            if (string.Equals(name, APP, StringComparison.InvariantCultureIgnoreCase)) return;

            if (!REFS.Any(x => x.Name.StartsWith(Path.GetFileNameWithoutExtension(name), StringComparison.InvariantCultureIgnoreCase)))
            {
                AppDomain.CurrentDomain.Load(Path.GetFileNameWithoutExtension(name));
            }
        }
    }
}