Shmuelie.WinRTServer 1.0.0

What is it?

The Component Object Model (COM) API that underlines .NET and the Windows Runtime supports the concept of Out Of Process (OOP) Servers. This allows for using objects that are in a different process (or even a different machine) as though they were in the local process. This library adds APIs to make the process of creating the "server" in .NET much easier.

Note: COM and Windows Runtime are Windows only.

Usage

Currently to create an Out-of-Process server requires the C++/WinRT tooling (though no actual C++ code) and a "contract" project. These two limitations will be removed in a future version of the library.

Contract Project

The contract project is a C# project that contains the interfaces of the remote objects. Output is a WinMD that is referenced by the other projects. The interfaces have some rules:

1. The interface must have a GUID assigned using the Windows.Foundation.Metadata.GuidAttribute attribute, not the System.Runtime.InteropServices.GuidAttribute attribute.

2. Asynchronous methods must use the WinRT types (IAsyncAction, IAsyncActionWithProgress<TProgress>, IAsyncOperation<TResult>, IAsyncOperationWithProgress<TResult, TProgress>) instead of Task and Task<T>.

3. Types in method parameters, type parameters, and return types must be:

   • A blittable type.
   • An interface that has a .NET/WinRT Mapping.
   • A WinRT type.
   • Another interface in the project.

4. Methods, properties, and events are all supported.

Metadata Project

The metadata project is a C++/WinRT project that uses MIDL 3.0 to create proxy types in a WinMD that can be referenced by the client of the OOP Server. No actual C++ code is needed, only the IDL.

The IDL is very simple, only needing runtimeclasses that implement the interface from the contract project. Unlike in C#, in MIDL 3.0 the type automatically has the members from the interface so they do not need to be listed again. Importantly the runtimeclass must have an empty constructor, otherwise the proxy type cannot be created.

❗Important: Because of the mix of SDK Style and C++/WinRT, nuget restore is needed to restore for C++/WinRT. In addition <RestoreProjectStyle>Packages.config</RestoreProjectStyle> is needed in the C++ project file.

Server Project

The server project is the only project that references Shmuelie.WinRTServer. It will contain implementations of the interfaces from the contract and when run should register them with an instance of COMServer. The implementations must have a GUID using the System.Runtime.InteropServices.GuidAttribute attribute.

Because the interfaces must use the WinRT asynchronous types instead of the .NET ones, the implementation will likely need to use AsyncInfo to help adapt between the two systems.

Client Project

An application to use the server project, using the metadata project to generate the proxy information. If the client is a UWP project, see this blog post for how to create the instances.

Sample

To help understand usage, a sample using a UWP client app is included under the test directory. Simply run the Shmuelie.WinRTServer.Sample.Package project to see it in action.

Note: If Visual Studio fails to build the Metadata project restarting Visual Studio should fix the problem.

Alternatives

If both applications are full trust applications other RPC/IPC technology might be easier to use. The main advantages of using COM/WinRT are that any language that can use COM can be the client and the runtime handles how to serialize/marshal types.

If the client is a UWP application, the options are more limited. AppServices from the Community toolkit is easier to use but does not support more complex scenarios that COM/WinRT OOP does like events, properties, and complex object graphs.