Dependency injection in the gaming world

This again?

As mentioned in the general section there are loads of different frameworks that allow you to achieve DI but in the game dev world things are often a bit trickier, this is down to how you need to often support multiple platforms (i.e windows, linux, ios, android, webgl etc) and also you are not always doing everything in code, you may be using the unity editor or some other scene first style approach, which means you have to take what is good about DI in general and apply it in a different way.

In the context of Unity there are not that many which are supported, so the main options are Zenject and StrangeIoC, although for this example we will use Zenject here purely because it is slightly more lightweight, as Strange IoC has a bit of conventions that come with it.

You can find all the documentation and information on their websites for both:

• Zenject
• StrangeIoC

As mentioned almost all DI frameworks share the same sort of principals, just the syntax is different and maybe the features offered.

Bindings

So to begin with Zenject has the notion of a MonoInstaller which is where it contains all binding setup, this is the same as a Ninject module.

using Zenject;

public class GameInstaller : MonoInstaller
{
    public override void InstallBindings()
    {
        Container.Bind<ISomething>().ToTransient<SomeImplementation>();
        Container.Bind<ISomethingElse>().ToTransient<SomethingElse>();
    }
}

As you can see, nothing really shocking. It is basically the same as the Ninject version we showed before, however in this case installers need to be registered with a type of context:

• ProjectContext (Allows you to load a set of bindings via installers across all scenes)
• SceneContext (Allows you to load an installer for a given scene)
• GameObjectContext (Allows you to setup GO level stuff, but we wont be going into that too much)

Here are some other examples of simple bindings:

Container.Bind<ISomething>().ToTransient<Something>(); // Bind it with transient scope
Container.Bind<ISomething>().ToSingle<Something>(); // Bind it with singleton scope
Container.Bind<ISomething>().ToInstance(new SomethingImplementation()); // Bind it to an instance

There are far more binding scenarios specific to Zenject such as binding to prefabs, methods, gameobjects, getters and far more, all available within the documentation on the site.

Resolving

Within Zenject you can do manual resolving quite easily given a container and just call Resolve<T>() on it, however given with a lot of Unity being scene driven it also allows you to inject into GameObject classes via attributes (as you cannot access the constructors of MonoBehaviour classes).

using Zenject;

public class MyMonoBehaviour : MonoBehaviour
{
    [Inject]
    public ISomeDependency SomeDependency { get; set; }

    [Inject]
    public void OnDependenciesResolved()
    {
        // All dependencies have been resolved
    }
}

This is only needed within MB classes as you still get to have constructor injection for any and all classes you have constructor access to.