To create your own control class, inherit from the System.Windows.Forms.UserControl, System.Windows.Forms.Control classes, or from the other Windows Forms provided controls. For more information about authoring custom controls, see Developing Custom Windows Forms Controls with the .NET Framework.

The System.Windows.Forms.Control class implements very basic functionality required by classes that display information to the user. It handles user input through the keyboard and pointing devices. It handles message routing and security. It defines the bounds of a control (its position and size), although it does not implement painting. It provides a window handle (hWnd).

Windows Forms controls use ambient properties so child controls can appear like their surrounding environment. An ambient property is a control property that, if not set, is retrieved from the parent control. If the control does not have a Control.Parent, and the property is not set, the control attempts to determine the value of the ambient property through the Control.Site property. If the control is not sited, if the site does not support ambient properties, or if the property is not set on the System.Windows.Forms.AmbientProperties, the control uses its own default values. Typically, an ambient property represents a characteristic of a control, such as Control.BackColor, that is communicated to a child control. For example, a System.Windows.Forms.Button will have the same Control.BackColor as its parent System.Windows.Forms.Form by default. Ambient properties provided by the System.Windows.Forms.Control class include: Control.Cursor, Control.Font, Control.BackColor, Control.ForeColor, and Control.RightToLeft.

Windows Forms has accessibility support built in, and provides information about your application that enables it to work with accessibility client applications such as screen enlarger and reviewer utilities, voice input utilities, on-screen keyboards, alternative input devices, and keyboard enhancement utilities. Sometimes you will want to provide additional information to accessibility client applications. There are two ways of providing this additional information. You can set the Control.AccessibleName, Control.AccessibleDescription, Control.AccessibleDefaultActionDescription, and Control.AccessibleRole property values, which will be reported to accessibility client applications. This method is typically used to provide limited accessibility information for existing controls. Alternatively, you can write your own class deriving from the System.Windows.Forms.AccessibleObject or System.Windows.Forms.Control.ControlAccessibleObject classes, providing as much accessibility information as needed.

The majority of the controls in the System.Windows.Forms namespace use the underlying Windows common control as a base to build on. For more information about the Windows common controls, see the "General Control Reference" topic in the MSDN library at http://msdn.microsoft.com/library.

To identify Windows Forms controls from a separate process, use a standard SendMessage call to pass the WM_GETCONTROLNAME message. WM_GETCONTROLNAME is independent of the language and Windows hierarchy. For more information, see the "Recommended Solution for Windows Forms" topic in the "Automating Windows Forms" section of the MSDN library at tp://msdn.microsoft.com/library.

Use the Control.InvokeRequired property to synchronize access to the control from multiple threads. For more information about multithreaded Windows Forms controls, see How to: Make Thread-Safe Calls to Windows Forms Controls