Middleware and Scoped/Singleton objects

Question

Can anyone explain what i'm missing here? I've created a simple application, using the default asp.net core 1.1 MVC template. I'm using the default DI container, and have made no other changes than to add a middleware class, and DI configuration.

The problem is that when using either Scoped or Singleton instances of an object, the same object is not being injected in both places.

Here's the code:

public class MyMiddleware
{
    private readonly RequestDelegate _next;

    public MyMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext httpContext, MyInstance myInstance)
    {
        httpContext.Items["myInstance"] = myInstance;
        myInstance.MyProperty = 99;

        await _next(httpContext);
    }
}

public class MyInstance
{
    public int MyProperty { get; set; }
}

In ConfigureServices I have:

services.AddSingleton();

In Configure I have:

app.UseMiddleware();

And in the Home Controller Index method I have:

public IActionResult Index(MyInstance myInstance)
{
    if (ReferenceEquals(HttpContext.Items["myInstance"], myInstance))
        Debug.WriteLine("Equal!");
    else
        Debug.WriteLine("Not Equal!");

    return View();
}

Regardless of whether I use Scoped or Singleton lifetimes, this always prints "Not Equal!". In addition, through debugging, I've verified that MyProperty on MyInstance is 0 in the HomeController Index.

Clearly, I'm missing something here. It does the same thing in .NET Core 2.0 Preview1 as well.

Any suggestions here?

EDIT:

As another test, I set MyProperty to a different value in HomeControll/Index and on the second refresh the value was back to 0 again, so obviously it seems to be creating a new transient instance every time.

Middleware and Scoped/Singleton objects

1 Answers