I just re-watched an excellent video by David Schwartz an Embarcadero MVP. Schwartz gave this presentation during a 2014 Code Rage 9 session.
Schwartz says the majority of Delphi code he has seen uses what he calls "Back-Door" injection. All the data movement to and from controls is handled at the form level. He discusses "Constructor" injection and "Property" injection pointing out the pros and cons of both.
I found this very interesting.
CodeRage9
Have You Embraced Your Inner Software Plumber Yet?
David Schwartz
Here are time jumps to specific sections:
00:41 Overview:
05:56 What We Do Today
12:00 "Back-door" Injection
12:42 Using Property Injection
14:35 Summary
21:51 Focus: Selection Forms
34:05 What Have We Learned?
35:38 Recommendations
36:42 Conclusions
External References: