Not understanding auto layout, constraints and size classes

Question

I'm a bit stuck and any help would be greatly appreciated!

I'll give you a quick overview. I have designs for a screen that were built in sketch using an iphone 6 screen size, then redesigned to fit and look right for an iphone 5/5s/5c, and 6 plus as those are the only devices that I want to support.

But the design portion or implementing the designs for just one specific screen size is easy and I understand that part. Where am I'm lost completely, is how to implement a design in one view controller that looks the way that it should in all the screen sizes I designed for.

I've gone through more than a few auto layout and size class tutorials and not sure how I properly use them so that the app recognizes "this is an iphone 5, use these image sizing and placements instead, and this is an iphone 6 plus, use these" and so on.

Everything I've seen to this point regarding auto layout and constraints only use 1 set of numbers to judge distance from elements for example, but all screen sizes would have different distances.

What am I missing or not understanding? I know I'm looking at something improperly.

Thanks in advance for all help!

Answer 1

You're correct that just one set of numbers could be used to judge distances, but this can still describe how a view should appear on different screen sizes. Your problem may be that you're thinking of constraints as describing the frame of your view? (Which obviously has to be different on every device). I find it more helpful to think of constraints as describing how each edge of my view relates to another view.

For example here's a view controller I setup with all the same constraints and how it would look on different devices. The constraints describe how the large grey view is pinned it's left and right edges 20 points from the left and right edges of its container view. It's pinned to 8 points from the top and 8 points from the top of the label. The label is centred vertically and horizontally and it has intrinsic content size. Each button is pinned 20 points from the bottom edge with button 1 and 2 being pinned to the 20 point from the left and right edges respectively.

I don't know if that helped or if that wasn't the answer you were after and you need to arrange your views differently depending on the device: you can tell Xcode which device size and orientation the constraints you're creating are for, using this button in Interface Builder.

Use it to select a device size/orientation. After, any constraints you create will only be used on that device. By default any width and height are selected so normally your constraints are applied to all devices.

Also, you cannot choose which devices you want to support, only the iOS version.