How to use multiple restrictions in C# Generics properly?

Question

I am attempting to bind c# generics to a class and an interface like this:

public class WizardPage<T> where T : UserControl, IWizardControl 
{
    private T page;

    public WizardPage( T page ) {
        this.page = page;
    }
}

And use it with this:

public class MyControl : UserControl, IWizardControl {
   //...
}

Somehow C# doesn't seem to be able to decide that MyControl is a proper instance of T as

public class Wizard<T> where T : UserControl, IWizardControl {

    private WizardPage<T> Page1;

    public Wizard( MyControl control ) {
        this.Page1 = new WizardPage(control);
    }
}

fails with error

The best overloaded method match for 'Controls.WizardPage<T>.WizardPage(T)' has some invalid arguments

Am I doing something wrong or is this just not going to work?

Answer 1

I don't get the Wizard class. Shouldn't it rather be something like this:

public class MyWizard : WizardPage<MyControl>{ 
    public MyWizard( MyControl control ) : base(control) { } 
} 

Answer 2

you have to declare the type used :

this.Page1 = new WizardPage<MyControl>(control);

Answer 3

Your Wizard class should probably look something like this:

public class Wizard<T> where T : UserControl, IWizardControl
{
    private WizardPage<T> Page1;

    public Wizard(T control)
    {
        this.Page1 = new WizardPage<T>(control);
    }
}

Or, if you don't need the class itself to be generic you could do something like this instead:

public class Wizard
{
    private WizardPage<MyControl> Page1;

    public Wizard(MyControl control)
    {
        this.Page1 = new WizardPage<MyControl>(control);
    }
}