What the use of inheriting from multiple classes?

Question

I saw some comments on forums, and it seems that people want to be able to inherit from multiple classes in c#. Why would you ever need this? I can't think of any use for this, but since there's people that want it, there's got to be some.

Answer 1

Well, here's an ASP.NET WebForms example:

I have one base class, a web control, let's say it is a simple TextBox.

I then inherit from the TextBox to provide formatting - RichTextBox.

I then want to have a TextBox that can spell-check - SpellCheckingTextBox.

What if I need a SpellCheckingRichTextBox? I would have to implement the spell checking or rich text logic again and inherit from one or the other.

In reality you would define them as interfaces: ISpellCheckingTextBox and IRichTextBox and implement them in a SpellCheckingRichTextBox. You could also write extension methods for TextBox to accomplish the same thing.

Multiple inheritance is fundamentally flawed because it views inherited classes as equal. What if both base classes had an ID field?

Answer 2

People probably want to do this because they are accustomed to doing it in C++. It isn't allowed in C#. Which, IMO, is a good thing, from an application maintainability point of view. Often times, using multiple interfaces will accomplish the same thing.n

If you have a base class with abstract methods properly designed and it's know that the inheriting object will only need the methods defined in that class, you have have a valid design pattern that doesn't require MI.