Question

I am creating a MDI form and I have a method that loads the different forms. Now I need to make a little modification – I need to add functionality that calls one child form from within another child form.

Because I need this in several different places I made a new class from who all the classes that need this functionality inherits. I want to make it work with generic types so I can pass every form class that I may need like LoadAForm(MyForm1) or LoadAForm(MyForm2) and so on.. I hope I it’s clear what I want as final result.

I tried this:

protected void LoadAForm<T>(ref T sender)
{
    MainForm frm = this.MdiParent as MainForm;
    T temp;
    if (frm != null)
    {
        sender  = SingletonFormProvider.GetInstance<temp>(frm, true);
        sender.MdiParent = frm;
        sender.Dock = DockStyle.Fill;
        sender.Show();
    }
}

which doesn’t work. But I have almost no experience with generics even more when they are used in methods, so I don’t know how to go on.

What I get as an error using this syntax is The type or namespace "temp" could not be found...". I'm not even sure that this is the way to do it.GetInstance<>` has to take an argument of the same type as the type of the form I’m calling.

Answer 1

You need to use the type parameter, not the variable name:

sender = SingletonFormProvider.GetInstance<T>(frm, true);

Also, to ensure that T is valid (as your comment suggests) you will need to constrain it:

protected void LoadAForm<T>(ref T sender) where T : Form