How to use Autofac with Winforms to inject a dependency

Question

I am trying to learn Autofac. I can't find a working example for Winforms. In my program.cs I have this:

public static IContainer Container { get; private set; }

/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
private static void Main()
{
     var builder = new ContainerBuilder();
     builder.Register(c => new MyContext());
     Container = builder.Build();
     ...
     using (var loginForm = new LoginForm(new MyContext()))
     {
         DialogResult results;
         do
         {
             results = loginForm.ShowDialog();
             if (results == DialogResult.Cancel)
                 Environment.Exit(1);
         } while (results != DialogResult.OK);
            
         UserName = loginForm.ValidatedUserName;
     }
}

MyContext() is a DbContext. I want to inject MyContext() into my LoginForm(), but I haven't quite figured that out. The first few lines of LoginForm():

public partial class LoginForm : Form
{
    private readonly MyContext _context;

    public LoginForm(MyContext context)
    {
        InitializeComponent();
        _context = context;
    }
    ...
}

Any suggestions would be appreciated.

Answer 1

Register the form too:

var builder = new ContainerBuilder();
builder.RegisterType<MyContext>();
builder.RegisterType<LoginForm>();
Container = builder.Build();

And then resolve the form from the container:

using (var loginForm = Container.Resolve<LoginForm>())
{
    DialogResult results;
    do
    {
        results = loginForm.ShowDialog();
        if (results == DialogResult.Cancel)
            Environment.Exit(1);
    } while (results != DialogResult.OK);
       
    UserName = loginForm.ValidatedUserName;
}

Then MyContext will automatically be injected when the form is resolved. By default Autofac registrations are registered as "self" (i.e. they can be resolved as their own type) and "instance per dependency" (you get a new one each time you resolve it), so you are safe to keep the using in this case.