VolocyNazad.Revit.MediatR 2025.0.9

Revit.MediatR

MediatR pipeline service implementations for the Revit API.

Revit.MediatR is a set of pipeline-pattern service implementations for the Revit API with support for DI containerization: commands and handlers that know how to marshal execution onto the Revit API thread via ExternalEvent (VolocyNazad.Revit.Events) and wrap it in a named transaction — without having to hand-write an IExternalEventHandler and Transaction at every call site.

Installation

dotnet add package VolocyNazad.Revit.MediatR

The package version is tied to the Revit year: {RevitYear}.0.{patch} (e.g. 2025.0.7). It is built for a specific Revit version depending on the selected build configuration — the same way as Revit_All_Main_Versions_API_x64, which the project depends on.

DI Registration

using Revit.MediatR.DI;

services.AddMediatR();

This call registers VolocyNazad.Revit.Events (AddEvents) and VolocyNazad.Revit.Context (AddRevitContext), then MediatR itself along with the handlers for the built-in lambda commands and the Revit-specific pipeline behaviours (RevitTransactionBehaviour, RevitExternalEventBehaviour), which automatically open a transaction and/or marshal execution onto the Revit API thread.

Built-in Commands

All of them run in the context of a document (either explicitly passed or the active one from IRevitContext) and return Response<bool> — a wrapper carrying the result, an error flag, a message, and an exception.

Example: transaction on the active document

Response<bool> response = await mediator.Send(
    new LambdaTransactionCommand(
        document: null!, // ActiveDocument is taken from IRevitContext
        transactionName: "Move wall",
        @delegate: (doc, ct) =>
        {
            // changes to the model
            return Task.FromResult(true);
        }));

Example: execution via ExternalEvent (e.g. from a WPF modal window)

Response<bool> response = await mediator.Send(
    new LambdaExternalEventTransactionCommand(
        document: activeDocument,
        transactionName: "Create level",
        @delegate: (doc, ct) =>
        {
            // code that must run on the Revit API thread, inside a transaction
            return Task.FromResult(true);
        }));

Custom commands

You can create your own commands by inheriting from Revit.MediatR.Base.DocumentCommand and implementing the marker interfaces Revit.MediatR.Abstractions.Models.ITransactionCommand and/or IExternalEventCommand, as well as writing an IRequestHandler<TCommand, Response<bool>> for them — the pipeline behaviours will pick them up automatically via these interfaces.

Supported Revit Versions

The package is built for every Revit version listed in the Configurations element of src/Revit.MediatR/Revit.MediatR.csproj (2021.1.9, 2023.0.0, and 2025.0.0), targeting net48 or net8.0-windows depending on the year — the switching and generation of define constants (IS2025, BEFORE2021, AFTER2021, etc.) is handled by the shared MSBuild SDK VolocyNazad.Revit.Sdk.

Development

• dotnet build --configuration "Release_2025.0.0" — build for a specific Revit version.
• dotnet test --configuration "Release_2025.0.0" — unit tests (tests/Revit.MediatR.Tests). Tests that need real Revit-typed objects (Document) to work are marked Skip — the RevitAPI/RevitAPIUI assemblies are not loaded outside of the Revit process.
• The package version is auto-versioned via MinVer from git tags of the form 0.0.7; to release a new version, create a tag and push it: git tag 0.0.7 && git push origin main --follow-tags.

License

MIT

Development documentation

• Development policy
• Repository guide and technology stack

Contributing

CONTRIBUTING.md before submitting changes.