Inherit from a base class

Add a colon immediately following the class name, followed by the name of the base class. Interfaces (if any) to be inherited are added after the single base class, separated by commas.

Render output from a control

Override the Render method of the control class from which the custom control is derived. To take advantage of the rendered output of controls such as TextBox and Label, call the Render method of the base class when you are finished rendering custom output.

Handle postbacks

Implement the IPostBackDataHandler and/or IPostBackEventHandler interfaces, and implement the methods defined by the interfaces.

Maintain state in a custom control

Store state in and retrieve state from the ViewState object in your property procedures.