Specifies a static value that is used by the property system rather than a null reference (Nothing in Visual Basic) to indicate that the property exists, but does not have its value set by the property system.
Namespace: System.Windows Assembly: WindowsBase (in windowsbase.dll)
UnsetValue is a sentinel value that is used for scenarios where the WPF property system is unable to determine a requested DependencyProperty value. UnsetValue is used rather than a null reference (Nothing in Visual Basic), because a null reference (Nothing in Visual Basic) could be a valid property value, as well as a valid (and frequently used) DefaultValue.
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.