How does TextView display (changes to) its text?

Question

I am wondering how android's android.widget.TextView is working. I went through the code of the class and searched for explanations, however, i was unable to figure out the key questions . Particularly i am interested in two parts:

1. How is text being displayed?
2. What happens when the TextView is editable (basically an EditText) and the user inputs a letter?

I know that at some point TextPaint is being used, however i could not figure out where it gets the canvas to draw on and how much exactly is being drawn (only the changed part or the entire text?).