Is there an equivalent to Form.InvokeRequired in WPF, e.g. Dispatcher.InvokeRequired?
This is slightly odd as it doesn't appear in intellisense, but you can use:
var dispatcher = myDispatcherObject.Dispatcher;
if (dispatcher.CheckAccess()) { /* ... */ }
As all UI components inherit from DispatcherObject
this should solve your specific problem, but it is not specific to the UI thread - it can be used for any dispatcher.