A
user control is a kind of composite control that
works much like an ASP.NET Web page —you can add existing Web server controls and markup to a user control, and define properties and methods for the control. You can then embed them in
ASP.NET
Web pages, where they act as a unit.
User controls are substantially easier to create, because you can
reuse existing controls. They make it particularly easy to create controls with complex user interface elements.
Refer:
ASP.NET User Controls Overview[
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If you have developed an
ASP.NET
Web page and would like to access its functionality throughout your application, you can make some minor alterations to the page to change it to a
user control.
Refer:
How to: Convert Web Forms Pages into ASP.NET User Controls[
^]
How to: Create ASP.NET User Controls[
^]
How to: Include ASP.NET User Controls in Web Pages[
^]