How to send_keys to view controller?

I asked this question on stackoverflow, but it did not receive much love. So I am trying again here. Since I am a new user I cannot post links, so here’s the question id, in case you want to have a look at the original and maybe claim some rep: 37864980

I have a view controller with custom text input, that the view controller itself is taking care of. So the view controller is setting itself as first responder and updates a view based on the input.

The problem is that I am now trying to add automated UI tests for this screen with Appium and I cannot find a way to send_keys to the view controller.

Does anyone have any idea how to do this?