When there are several windows on the screen, the active window is the frontmost and has a highlighted title bar. A window becomes the active window when the user clicks somewhere inside it. The active window is said to “have the focus.” For example, in Visual Studio the active window is the Toolbox when you’re selecting an item from it, or the Properties window when you’re editing a control’s properties.

A Form is a container for controls and components. When you drag an item from the Tool-box onto the Form, Visual Studio generates code that creates the object and sets its basic properties. This code is updated when the control or component’s properties are modified in the IDE. Removing a control or component from the Form deletes the corresponding generated code. The IDE maintains the generated code in a separate file using partial classes—classes that are split among multiple files and assembled into a single class by the compiler. You could write this code yourself, but it’s much easier to allow Visual Studio to handle the details. We introduced visual programming concepts in Section 2.6. In this chapter and the next, we use visual programming to build more substantial GUIs.

Each control or component we present in this chapter is located in namespace System.Windows.Forms. To create a Windows Forms app, you generally create a Windows Form, set its properties, add controls to the Form, set their properties and implement event handlers (methods) that respond to events generated when a user interacts with the controls. Figure 14.4 lists common Form properties, common methods and a common event.