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One of the most common questions in any Windows programming language is how to add a control to a window dynamically—in other words, while the program is executing. For example, you might want to create a program that generates tailored forms based on the information in an XML file. This sort of task is surprisingly easy in .NET, because there isn’t a sharp distinction between control creation at runtime and control creation at design time. In fact, in .NET programming, control is created through code. As you learned in Chapter 1, when you add a control to a form and configure its properties, Visual Studio generates the appropriate code statements and adds them to a designer file. By studying this automatically generated code, you can quickly learn how to create and add any control you need at runtime.

Help: Is it the final polish on a professional application, or a time-consuming chore? It all depends on the audience, but most applications need a support center where users can seek assistance when they become confused or disoriented. Without this basic aid, you (or your organization’s technical support department) are sure to be buried under an avalanche of support calls.

There’s a whole class of Windows applications that don’t resemble the examples you’ve seen so far. They use highly stylized interfaces with shaped windows and animated buttons, and often look more like a Flash-animated Web page or futuristic dashboard than a typical Windows Forms user interface.

Drawing programs exist in two basic flavors. The first type is painting programs, like Microsoft Paint, which allow users to create bitmaps with static content. In these programs, once the user draws a shape or types some text onto the drawing area, it can’t be modified or rearranged. But in more-sophisticated drawing programs (everything from Adobe Illustrator to Microsoft Visio), the user’s drawing is actually a collection of objects. The user can click and change any object at any time or remove it entirely.

Extender providers are a specialized type of component that can enhance other controls. Essentially, an extender provider works by adding “virtual properties” to existing controls. For example, the ErrorProvider adds an Error property that you can set to display a flashing error icon next to input controls that contain invalid information. Other examples include the ToolTip, which displays a tooltip next to other controls, and the HelpProvider, which invokes context-sensitive Help on a control’s behalf when the F1 key is pressed. Chapter 4 introduced the basic extender providers included with Windows Forms. These are prebuilt components, but you can also build your own.

In Chapter 13 you explored how you could add a respectable level of design-time support to your control. You saw how attributes, type converters, and type editors could improve the Properties-window support for your control and ensure proper code serialization. In this chapter, you’ll continue to add to your design-time skills by considering a few more topics.