Visual Basic® 2008 Programmer's Reference

Chapter 22. Custom Controls

Visual Basic .NET provides a rich assortment of controls that you can use to build applications. Nevertheless, those controls may not always be able to do what you need. In that case, you may want to build a control of your own. Building your own control lets you get exactly the behavior and appearance that you want.

Custom controls solve three significant problems. First, they let you package a particular behavior or appearance so that you can easily reuse it later. If you need to draw one engineering diagram, you can draw it on a PictureBox. If you need to draw many engineering diagrams (possibly in different applications), it would be easier to make an EngineeringDiagram control that can make all of the diagrams.

Second, developers are familiar with controls and comfortable using them. Any experienced Visual Basic developer understands how to create instances of a control, set its properties, call its methods, and respond to its events. If you build a custom control to perform some complex task, developers already know a lot about how to use it. You just need to explain the specific features of your control.

Finally, controls can easily save and restore property information at design time. A developer can set properties for a control at design time, and the control uses those properties at runtime. This is useful for graphical controls, where properties such as Text, BackColor, and BorderStyle determine the controls' appearance. It is also useful for ...