What is the difference between User Control, Custom Control and Component?

Question

These are three different things you can add to a project and I am not quite sure if I understand the difference. They all seem to for example show up in the component toolbox when working with a Form. What are some common usage scenarios for each of them? What is the difference?

Answer 1

The main difference between User Control, Custom Control and Component is that they inherit from different levels in the inheritance tree:

MyComponent    |-> Component  MyCustomControl    |-> Control           |-> Component  MyUserControl    |-> ContainerControl           |-> ScrollableControl                  |-> Control                         |-> Component 

So, in short you get a different amount of pre-wired functionality with the different options.

When would you use the different options? (these are thoughts and opinions, not truths)

• Create a component if you want to provide functionality without UI (such as Timer components, data sources, ...)
• Create a custom control if you want to make a component where you have full control over its visual appearance, and you don't want any baggage of unnecessary functionality. Typical cases would be simple controls with limited functionality (such as a button)
• Create a user control if you are going to combine existing controls into reusable building blocks (such as two lists with buttons where you can move items between the lists).