PianoKeyboard | A Piano Keyboard implemented in Swift | Keyboard library

This is totally mysterious. I checked everything, googled everything, but looks like this should work. I've done same things in my code with others html elements and they all give me the values, but this time I'm getting undefined for this particular HTML element. The snippet of code below:

I am trying to write a XAML control for a Piano Keyboard in WPF which responds to NoteOn and NoteOff MIDI events from an external MIDI keyboard. I am using Tom Lokovic's midi-dot-net to raise NoteOn and NoteOff events triggered by the hardware but I need a way to get these events to raise the NoteOn and NoteOff events of my XAML Key class (derived from the WPF Button). The colour of a key should change when it is on and the event should be subscribable to so that a user of the Piano Keyboard control can play a sound the key is pressed.

I could do this by passing every Midi.InputDevice to every single key on the keyboard so that each one can subscribe to the NoteOn and NoteOff events of every InputDevice then, in turn raise their own NoteOn and NoteOff events but the problem with this is that the PianoKeyboard control (an ItemsControl which holds Keys) and its nested Key controls all become tightly coupled to the implementation of midi-dot-net. If I have to do this I will, but it seemed like there should be a better way of doing this in WPF moving the dependency on midi-dot-net higher up in the call stack.

I have too much code to paste in its entirety here and still be readable so here's a sample of one of the DataTemplates I'm using as my PianoKeyboard's ItemTemplate.

Essentially what I'm asking is: given an input device is not supported to trigger a WPF button with the button's built in behaviour (e.g. a mouse click), how does one get it to trigger the button without coupling it to a derived class of the button?