Control Class

To create your own control class, inherit from the UserControl, 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 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 Parent, and the property is not set, the control attempts to determine the value of the ambient property through the 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 AmbientProperties, the control uses its own default values. Typically, an ambient property represents a characteristic of a control, such as BackColor, that is communicated to a child control. For example, a Button will have the same BackColor as its parent Form by default. Ambient properties provided by the Control class include: Cursor, Font, BackColor, ForeColor, and RightToLeft.

Note

To make your Windows Forms application support Windows XP visual styles, be sure to set the FlatStyle property to System and include a manifest with your executable. A manifest is an XML file that is included either as a resource within your application executable or as a separate file that resides in the same directory as the executable file. For an example of a manifest, see the Example section of the FlatStyle enumeration. For more information about using the visual styles available in Windows XP, see "Using Windows XP Visual Styles" in the MSDN library at http://msdn.microsoft.com/library.

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 AccessibleName, AccessibleDescription, AccessibleDefaultActionDescription, and 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 AccessibleObject or Control.ControlAccessibleObject classes, providing as much accessibility information as needed.

Note
To maintain better performance, do not set the size of a control in its constructor. The preferred method is to override the DefaultSize property.

Note
Do not add data bindings for a Control in its constructor. Doing so will cause errors in code generation and can cause unwanted behavior.

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 http://msdn.microsoft.com/library.

Use the 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

.NET Framework

.NET Framework Client Profile

Windows 8 Release Preview, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 SP2, Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Only the following members are thread safe: BeginInvoke, EndInvoke, Invoke, InvokeRequired, and CreateGraphics if the handle for the control has already been created. Calling CreateGraphics before the control's handle has been created on a background thread can cause illegal cross thread calls.

Reference