Revit Assembly Resolution

Revit Assembly Resolution

Revit does not probe an add-in's folder for dependencies; loading a window or third-party assembly can throw FileNotFoundException. ResolveHelper (from Nice3point.Revit.Toolkit) redirects resolution to a type-adjacent or explicit folder for the scope's lifetime. Scopes nest — the innermost is searched first.

When to use

• A dependency or WPF window fails to load with a resolution error.
• Isolating a conflicting assembly version for a bounded operation.

When not to use

• Inside an entry point derived from the Toolkit base classes (ExternalCommand, AsyncExternalCommand, ExternalApplication, ExternalDBApplication) — they already open a resolve scope; a manual one is redundant.
• Preventing two add-ins from loading conflicting versions of the same dependency process-wide — that is revit-dependency-isolation.

Workflow

Step 1: Wrap the load in a resolve scope

using (ResolveHelper.BeginAssemblyResolveScope<Application>())
{
    var window = new SettingsWindow();
    window.Show();
}

The generic and typeof(...) overloads probe the folder of the given type's assembly. Pass an explicit directory when the dependencies live elsewhere — a shared or external libraries folder:

using (ResolveHelper.BeginAssemblyResolveScope(@"C:\Libraries"))
{
    return LoadExternalLibrary();
}

Step 2: Scope it tightly and nest for isolation

Open the scope only around the load that needs it, and nest scopes when a dependency version must be isolated from an outer one.

Step 3: Verify

Confirm the dependency loads without a resolution error, and that resolution behavior is restored after the scope disposes.

Validation

• The scope wraps the specific load that fails to resolve.
• Entry points rely on the base classes, not a manual scope.
• The scope disposes, restoring normal resolution.

Common Pitfalls