Tài liệu Creating Custom .NET Controls with C#

Windows programmers have a wide variety of controls to choose from in the System.Windows.Forms
namespace in .NET's Framework class library. You have controls as simple as Label, TextBox, and CheckBox,
as well as controls as sophisticated as the MonthCalendar and ColorDialog controls. These Windows controls
are more than enough for most applications; however, sometimes you need controls that are not available from
the standard library. In these circumstances, you have to roll up your sleeves and write your own. This article
shows you how to develop a custom control with C# and presents a simple custom control.
Before you start writing the first line of code for your custom control, you should familiarize yourself with two
classes in the System.Windows.Forms namespace: Control and UserControl. The Control class is important
because it is the parent class of Windows visual components. Your custom class will be a descendent of the
Control class as well. Your custom controls, however, don't normally inherit directly from the Control class.
Instead, you extend the UserControl class. The first two sections of this article discuss these two classes. In
the final section, you'll build your own custom control, the RoundButton control.