How to Implement Dependency Injection in .NET Web API project

Here is an example of how you could implement dependency injection in a .NET Web API project.

First, create an interface for the service that you want to inject:

public interface IMyService
{
    string GetMessage();
}

Next, create a class that implements the interface:

public class MyService : IMyService
{
    public string GetMessage()
    {
        return "Hello, world!";
    }
}

In your Web API project, register the service with the dependency injection container (in this example, we'll use the built-in ASP.NET Core DI container):

public void ConfigureServices(IServiceCollection services)
{
    // Register the service with the DI container
    services.AddScoped<IMyService, MyService>();

    // Other configuration code...
}

Finally, inject the service into a controller or other component that needs it:

public class MyController : ControllerBase
{
    private readonly IMyService _myService;

    public MyController(IMyService myService)
    {
        _myService = myService;
    }

    [HttpGet]
    public IActionResult Get()
    {
        var message = _myService.GetMessage();
        return Ok(message);
    }
}

In this example, we've registered `MyService` as an implementation of the `IMyService` interface using the `AddScoped` method, which means that a new instance of `MyService` will be created for each HTTP request.

We then inject `IMyService` into our `MyController` using constructor injection, which allows us to use the `GetMessage` method of `MyService` in the `Get` method of our controller.