视图背后的魔法自动适应 ios13 暗模式？

Question

I found it quite weird that for new projects created by xcode 11 beta, common views like UILabel , UIButton in a storyboard can automatically adapt themselves to system theme changes without any code. But for my old projects still using XIB, even though all colors are set to default, they dont change when system theme changed, i still have to manually override traitCollectionDidChange and assign them system default values in order to make them change! What am i doing wrong? thanks.

Answer 1

I figured out. The magic is the newly added system colors to UIColor on ios 13, for example, UIColor.systemBackgroundColor , it will be white in light mode and black in dark mode, once you assign a system color to a property, it always updates itself based on system theme. So i guess UIViews created in xcode 11 beta storyboards automatically have system colors on.