CustomControl versus a UserControl

 Difference between a Custom Control and a User Control, I guess. Let's summarize the differences again. Read the comparison below to make things clear:

Custom Control	User Control
A loosely coupled control w.r.t code and UI	A tightly coupled control w.r.t code and UI
Derives from Control	Derives from UserControl
Defines UI in a ResourceDictionary	Defines UI as normal XAML
UI is skinable	Child controls are skin able
Has dynamic layout	Has static layout
UI can be changed in different projects	UI is fixed and can't have different looks in different project
Has full toolbox support	Can't be added to the toolbox
Defines a single control	Defines a set of controls
More flexible	Not very flexible like a Custom Control
Requires in-depth knowledge of Silverlight UI Model	Does not require in depth knowledge of the UI Model

Hope you now have a better understanding from the above comparison table.

When to use?

Good question: "When to use a Custom Control?" Haven't you got the inner meaning of it yet? OK, read the summarized points below:

·         When you have a rapid and fixed content in your UI, use UserControl.

·         When you want to separate some basic functionality of your main view to some smaller pieces with reusability, use UserControl.

·         When you want to use your control in different projects and each project may want to change the look, use CustomControl.

·         When you want to implement some additional functionality for a control, create a CustomControl derived from the base control.

·         When you want to apply themes to your controls, use CustomControl.

·         When you want to add toolbox support for your control, so that your user will be able to do drag and drop to the designer, use CustomControl.