This isn't true at all. Since iOS launched there has been UIKit and then this SwiftUI.
This isn't true at all. Since iOS launched there has been UIKit and then this SwiftUI.
They didn't say anything about iOS. There have been lots of UI frameworks from Apple, some abandoned before they were even finished:
QuickDraw, Quickdraw GX, HIToolbox, AppKit, Cocoa Touch/UIKit, Playgrounds/IB, SwiftUI
The constantly changing frameworks and languages are a useful strategy from platform vendors - they do help provide platform lockin, and make it very very difficult to provide cross platform apps. That is a real threat to Apple with offerings like flutter from Google. Of course there are other reasons to make a clean break with the past, but there is a lot of work just to stand still in developing for a platform like Mac OS or IOS - they don't highly value backwards compatibility and often introduce sweeping changes. Constant change is in the platform vendor's financial interest, and I don't think it's unfair to point that out.
Just to take one example - apps built for the original iOS are now almost entirely obsolete, and it's not worth reusing any of their code in a modern swift app.
You're saying that MacOS has been around a long time, which is true.
Development philosophies change over time, like the other's said, some of those UI frameworks you mentioned are 20+ years old.
It does suck that we can't use it on other platforms, and I'm sure they don't want to spend resources on doing so, but there's no way the main motivation is to keep people switching frameworks constantly.
If they don't control the language and tools for the platform, they don't control the platform.
Yes you're right there are various levels here - sometimes it's hard to distinguish them. There have definitely been at least 5 UI toolkits though, and probably more, though of course over the life of Mac OS that is not terribly unexpected. For those who lived through the transition to OS X, this sort of churn is not unusual, and I do think it does benefit platform vendors - they have zero incentive to keep supporting their technologies over decades and every incentive to increase churn.
Quickdraw GX I remember particularly because there was such fan-fair about it as a replacement for all your graphical needs (such as drawing text), and yet it was dropped before it could even really be used (same with Quickdraw 3D). I can't remember what apple called their UI toolkit at the time, which was based on Quickdraw, then GX, but I don't think it was Carbon, that came later didn't it? I think I've found it now, was it MacApp?