How to change controller property from component?

I have a property in the controller. I want to use a component to update that controller property. The usual component parameter passing works when I'm using a text field like the guides say, but in my case, I'm changing the value in code, not input fields. The binding seems to be broken.

What method similar to propertyDidChange() or notifyPropertyChange() should I use to accomplish this? Can you also provide a simple example so I know WHERE to make that method call?