Dependency Injection

ASP.NET Core supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies.

Registration

Register your dependencies in ConfigureServices.

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

    services.AddScoped<IMyDependency, MyDependency>();
    services.AddTransient<IOperationTransient, Operation>();
    services.AddScoped<IOperationScoped, Operation>();
    services.AddSingleton<IOperationSingleton, Operation>();
    services.AddSingleton<IOperationSingletonInstance>(new Operation(Guid.Empty));

    // OperationService depends on each of the other Operation types.
    services.AddTransient<OperationService, OperationService>();
}

Transient

Transient lifetime services (AddTransient) are created each time they're requested from the service container. This lifetime works best for lightweight, stateless services.

Scoped

Scoped lifetime services (AddScoped) are created once per client request (connection).

Singleton

Singleton lifetime services (AddSingleton) are created the first time they're requested (or when Startup.ConfigureServices is run and an instance is specified with the service registration). Every subsequent request uses the same instance.

Usage

public class SomeClass
{
    private readonly IMyDependency _myDependency;

    // injection through constructor
    public SomeClass(IMyDependency myDependency)
    {
        _myDependency = myDependency;
    }
    
    public void DoSomeWork()
    {
        // some logic here that can use _myDependency
    }
}