What is the difference of intrinsic size vs system width/height constraints?

Question

Starting to move from springs and structs layout to auto layout and have some questions regarding "Intrinsic Size" setting.

If you set "Intrinsic Size" of some view to "Placeholder" and put some width and height values then the view will not scale and will stay of the fixed size. But if we set "Intrinsic Size" to "Default (System defined)" then the system will decide and scale the view if needed during runtime.

However, we could explicitly set width and height system constraints to the view by using Ctrl + Drag. In such case there would be system width and height constraints AND const placeholder values. I'm reviewing existing code and trying to understand is it a bug and redundant system width and height constraints should be removed OR there's some other hidden logic. However, Xcode does not show any warnings and etc in console during runtime. Here's a print screen of demo project:

Answer 1

When you set the intrinsic size to "Placeholder", you tell the Xcode layout system that your view will have size dependent on its content (like a label can be dependent on its text content). The system only knows and maintains its own types of views with intrinsic size. If you wish to have a similar experience with a view of your own, to consider the view as if it has an intrinsic size. Then you set up your constraints as if the view should grown or shrink depending on its content. Finally, you implement the intrinsicContentSize method to calculate and return the correct size of the content. If the content changes and a new calculation should be performed, you call invalidateIntrinsicContentSize on your view. Depending on how you have set up your constraints, your view will either grow and/or shrink, or it will be static (like you can set a width and height constrains on a label, and it remains static).