Generic forms and VS designer

Question

I have a base class

internal partial class View : UserControl
  where T : class
{
    protected T t;
}

and I want to derive a chil

Answer 1

Generics break the designer because it cannot instantiate the class without a type T. I explain a workaround in my blog post:

http://adamhouldsworth.blogspot.co.uk/2010/02/winforms-visual-inheritance-limitations.html

In short, you need to "resolve" the type with an intermediary class:

• BaseControl : UserControl
• CustomerControl_Design : BaseControl
• CustomerControl : CustomerControl_Design

You can then conditionally switch this class out of the code based on the DEBUG or RELEASE compiler switches:

#if DEBUG

namespace MyNamespace
{
    using System;


    public partial class CustomerEditorControl_Design : BaseEditorControl
    {
        public CustomerEditorControl_Design()
            : base()
        {
            InitializeComponent();
        }
    }
}

#endif

    public partial class CustomerEditorControl
#if DEBUG
        : CustomerEditorControl_Design
#else
        : BaseEditorControl
#endif
    {
    }

This will let you open the derived class of CustomerControl, unfortunately you will never be able to design a UI control with generics in the signature. My solution is only enabling the design of derived items.

I have no idea why CustomerControl : BaseControl won't work as in this case the type T is defined, but it simply doesn't - I'm guessing because of the rules of generic usage.

To their defense, Microsoft do say that this isn't supported.