Dependency Injection Into {get; set;} Property

Question

I was wondering how I'd go about setting up my Dependency Injection to inject a dependency into properties that have public getters and setters ({get; set}).

So, an example would be:

namespace Dexter.Services {

    public class CommandHandlerService : InitializableModule {

        public CommandService CommandService { get; set; }

    }

}

With the following dependency injector:

namespace Dexter {

    public static class InitializeDependencies {

        public static async Task Main() {

            ServiceCollection ServiceCollection = new();

            CommandService CommandService = new();
            ServiceCollection.AddSingleton(CommandService);

            Assembly.GetExecutingAssembly().GetTypes()
                    .Where(Type => Type.IsSubclassOf(typeof(InitializableModule)) && !Type.IsAbstract)
                    .ToList().ForEach(
                Type => ServiceCollection.TryAddSingleton(Type)
            );


            ServiceProvider = ServiceCollection.BuildServiceProvider();

            // Initialization stuff.
        }

    }

}

In this example, I would like the CommandService to automatically inject into the property.

I know this is possible because Discord.NET is able to do this, and I'd love to stick with that same codestyle.

( Discord.NET: https://docs.stillu.cc/guides/commands/dependency-injection.html )

Thanks! <3

user_10874844 · Answer

For anyone curious, as per what Panagiotis recommended, a solution to this would be to create your own dependency injection. As such, I wrote a small method that loops through all the services in the provider, and attaches public properties to it. It may have bugs! Particularly regarding scoped services, of which I haven't written for it to support, but this should work as a good starting point for someone wishing to achieve a similar result!

public static object SetClassParameters(this object newClass, IServiceScope scope, IServiceProvider sp)
{
    newClass.GetType().GetProperties().ToList().ForEach(property =>
    {
        if (property.PropertyType == typeof(IServiceProvider))
            property.SetValue(newClass, sp);
        else
        {
            object service = scope.ServiceProvider.GetService(property.PropertyType);

            if (service != null)
            {
                property.SetValue(newClass, service);
            }
        }
    });

    return newClass;
}

Where you can use a method like the following to inject dependencies into classes. For instance, I wished to inject them into classes that extended an abstract "event" class that I made. This can be seen below:

using (var scope = serviceProvider.CreateScope()) {
    GetEvents().ForEach(
        type => serviceProvider.GetRequiredService(type).SetClassParameters(scope, serviceProvider)
    );
}

Where GetEvents() is a reflexive function that returns all classes extending the abstract class given.

user_980059 · Answer

This can be done without having to swap out the default DI container (IServiceProvider) using the Quickwire NuGet package.

Simply decorate your service with the [RegisterService] attribute and add [InjectService] to the property. No need for the interface.

[RegisterService(ServiceLifetime.Singleton)]
public class CommandHandlerService {

    [InjectService]
    public CommandService CommandService { get; set; }

}

Now from your main function, just call ScanCurrentAssembly:

public static async Task Main() {

    ServiceCollection ServiceCollection = new();

    ServiceCollection.ScanCurrentAssembly();

    ServiceProvider = ServiceCollection.BuildServiceProvider();

    // Initialization stuff.
}

Behind the scenes, ScanCurrentAssembly does all the necessary wiring to resolve dependencies, instantiate the class and inject it into properties.

Dependency Injection Into {get; set;} Property

2 Answers