iOS Top Alignment constraint based on screen (superview) height

Question

Let's say for example i want my view's top margin be

30 px for iPhone 6s

and for the other screen i want to change this constants from 30 to X where X is proportional to total height of screen

i.e.

36.5 for iPhone X, 33 for iPhone 6s plus, 25 for iPhone SE

And so on .... I know i can take @IBOutlet of NSLayoutConstraint and change it programmatically but what i want is i want to set it like aspect ratio that we have for height width like subview's heigh width is proportional it's superview it changes with super view's height and width

Answer 1

This is not possible on just a top constraint like you have. There isn't a way to associate top distance with height from interface builder.

You can add a view above your image that only exists to provide that padding. Your hierarchy will look like this in VFL:

"V:|[paddingView][imageView]"

Here's an image of the view in place above the image view:

Then you can install a height constraint on that padding view that makes it equal to the containing view.

Add a multiplier to that constraint that gets you the expected height. If you want it to be 30 on a screen that's 667 points tall, then the multiplier will be something like 0.044978 (30 / 667 = ~0.044978). This height constraint will update depending on the main view height which will provide the desired visual padding.

Answer 2

The constraint you need here is the superView's centerY set multiplier to 0.5 if you want the top anchor's constant to be 0.25 of screen height from the top , so adjust the multiplier according to this logic which is

height_of_screen = 2 * centerY