在由具有 .net 内核的应用程序加载的程序集中，通过反射查找所有特定类型

Question

Note: although the example code is in F#, I'm not specifically looking for a F# answer but for the .net calls I need to do, so an answer in C# or F# is fine.

I have a system where there are commands, for a chat bot, scattered in different part of the code. I find, and register, them all through reflection using this code:

member private this.RegisterCommands() =
    let t = typeof<IBotCommands>
    t.Assembly.GetTypes()
    |> Seq.filter (fun x -> x.GetInterface(t.Name) <> null)
    |> Seq.iter (fun x ->
        (
            let i = (Activator.CreateInstance(x)) :?> IBotCommands
            botCommands.[i.Name()] <- i
            i.Initialize(this)
        )
    )

It's in F#, but I think the method calls give away what it does if you're more familiar with C#.

So, I do Assembly.GetTypes, keep the ones where GetInterface has the interface name I'm looking for and then I instantiate them.

This works well, but only within its own assembly. My question is how can I expand this to all assemblies loaded by the app (but the system ones to not waste time)?

Answer 1

You can use Assembly.GetReferencedAssemblies on t.Assembly , filter out System references by their name and then Assembly.Load on the names to load a sequence of assemblies. From there you can do a Seq.collect on Assembly.GetTypes() .

Answer 2

Have your user assemblies define an assembly level attribute - which you can check for, to decide further scan the library. This is more robust than figuring out which assemblies to black-list, for eg, you may not want to scan Newtonsoft.Json .

   Assembly
       .GetEntryAssembly()   
       .GetReferencedAssemblies()    
       |> Seq.map    (fun assm -> Assembly.Load assm.FullName)
       |> Seq.append (Seq.singleton (Assembly.GetEntryAssembly()))
       |> Seq.filter (fun assm -> assm.IsDefined(useAttrib) )
       |> Seq.collect(fun assm -> assm.GetTypes())       
       |> Seq.filter (fun x -> interfaceType.IsAssignableFrom(x))
       |> Seq.iter (printfn "%A")

If your requirements are going to be more complex in the future, it might be worth taking a look at MEF.

let catalog = new DirectoryCatalog("./")
let container = new CompositionContainer(catalog)
container.ComposeParts()

let instances = container.GetExports<IBotCommands, IBotCommandMetadata>()