DispatchTimer | based NSTimer analogue that you can also pause

What you should do is to inject your view model with an interface that has a RunOnUIThreadAsync method or similar.

You would then create a class that implements this interface and calls Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync in the UWP app where you can assume that the CoreApplicationView is always available.

In your unit tests against the view model where there is no CoreApplicationView, you could simply mock the interface.

The other option would be to look into the BindingOperations.EnableCollectionSynchronization API that lets you access the collection from multiple threads.

The ImageSource property on ImageBrush doesn't automatically convert file paths to ImageSource object. You will have to do the conversion in your code:

Form.RosterBrowser.Document returns a reference to the browser Document, so lastDoc and thisDoc are two references pointing to the same HTMLDocument object which sits somewhere on the memory heap.

Instead you should store the value you are monitoring.
You'd better monitor the text itself and not only its length as the text can be changed but keeping the same length.

Dmitri is correct, I should have been using a Timer and not a DispatchTimer. Once I moved to that it worked fine.

Well, i'm no professional (which will be evident by the long way i've come up with a solution, i'm sure someone who does it for a living could get it done much more eloquently) but here's what i came up with as it seemed like a fun task.

I've got it stating a timer on launch, then when the button is clicked a new thread is started in the background, that new thread increments a counter every second, and timer1_tick is constantly checking what the counter value is and adjusting the form and textboxes accordingly, it's changing the colour, putting the number in and making it the focused item.

You'll need the following items on Form1: Textboxes 1 to 12 (in the pattern you provided with 12 being the top one) A button (Button1) Drag a timer (Timer1) onto Form1

Then replace the code on Form1 with the below

Your problem is that your code doing: