How to design Windows Forms with Abstract Inheritance?

It happened few days ago when I got to this nice error:

The designer must create an instance of type '... .BaseClass.TabBaseControl' but it cannot because the type is declared as abstract.

The scenario was like this: I had a Base class where a defined abstract members that where implemented in a form. When wanted to see the design of the page this warning appeared even though the application runs just fine. So how to get rid of this error:  "The designer must create an instance of type 'SchedeMaterialiDaTaglio.BaseClass.TabBaseControl' but it cannot because the type is declared as abstract. " ?

Well, searching around I got to this post http://www.platinumbay.com/blogs/dotneticated/archive/2008/01/05/designing-windows-forms-with-abstract-inheritance.aspx where I found part of the solution. 

Here it is:

 public class AbstractCommunicatorProvider : TypeDescriptionProvider
    {
        public AbstractCommunicatorProvider()
            : base(TypeDescriptor.GetProvider(typeof(UserControl)))
        {
        }
        public override Type GetReflectionType(Type objectType, object instance)
        {
            return typeof(UserControl);
        }
        public override object CreateInstance(IServiceProvider provider, Type objectType, Type[] argTypes, object[] args)
        {
            objectType = typeof(UserControl);
            return base.CreateInstance(provider, objectType, argTypes, args);
        }
    }

You define this class in inherited class(it only worked for me in this way) and you must also put this for base class and inherited class:

    [TypeDescriptionProvider(typeof(AbstractCommunicatorProvider))]
    public partial class TabUC : TabBaseControl{}

    [TypeDescriptionProvider(typeof(AbstractCommunicatorProvider))]
    public abstract class TabBaseControl : UserControl, ITabBase{}

Of course that you will have to include System.ComponentModel namespace and others just as needed.
Hope it helped. Ciao.

How to solve "Object reference not set to an instance of an object" in Design Time, Visual Studio, Winforms?

If you ever encounter this nice message then here is what you should do in order to fix "Object reference not set to an instance of an object" showing in Design Time even if code runs just fine.

I will tell you how I encountered it. I created a user control that has a property. In a page form I included this user control among others. In control's Load event I had to use that defined property. And I did not understood why it needs to know the value in design time, however it shows this nice error. It is obvious that is not set. It is only set when running.
So. Ready with long talk. The only think you need to get away of this "Object reference not set to an instance of an object" error you must use DesignMode property of the control. :)

if (!this.DesignMode)
{
   //your code here that generates the error
}

Well, hope that I helped you today with this error. Keep up the good code ;)