问题
I know what the solid ones are: I created them myself. What about the gray ones? Implicit, maybe via size-to-fit? The gray height conflicts with the solid height. Where do the gray ones come from?
回答1:
You are inspecting an object such as a label that has an intrinsic content size. The intrinsic content size generates height and width constraints; that's what intrinsic content size is. The constraints in gray are showing you the constraints that the intrinsic content size generates. If you just look at them, you can see that: they say "content size"!
They are in gray because they are overridden by your explicit constraints (they have a lower priority). But they are still there, and if you were not overriding them, they would take effect (and they would not be gray).
来源：https://stackoverflow.com/questions/28058590/what-are-gray-constraints-in-xcode-view-hierarchy-debug-view