We can add adaptivity to any subclass of UIView which we add on view controller in nib file.
Lets take an example of adding adaptivity using size classes to a view.

1. Add a view on view controller as:

2. Now we need to pin this view to it's superview for fixing it's size and position using constraints as:

3. We can see the added constraints as:

These constraints defines that the added view will be placed in it's superview as

CGRect(20, 0, superview.width - 20, superview.height - 20)

4. To see the preview on screen of these added constraints we can use Assistant Editor as;

5. We can add more screen to see preview like:

We can also see the preview with landscape mode by moving mouse on the name of device and clicking the rotation button as: