1. What is the difference between user control and custom control in WPF?
a). UI which will be used repeatedly in project, using usercontrol is a much simpler and preferred way
b). a portion of UI and functionality which you believe will be used across different projects, then using custom control is the right approach.
c). a user control doesn't support controltemplate and themes. But creating a usercontrol is much like creating a normal window with codebehind. A usercontrol exists of a xaml-file and a codebehind-file. Define eventhandlers in xaml and implement them in code.
d). a custom control supports controltemplates and themes. A custom control is a "lookless" control. The logic is in a code-file (.cs) and the look is defined in a controltemplate that is part of a style.
e). all the above