centerXAnchor和center.x之间的区别

Question

As far as I know the two main ways to center an element horizontally is to use the following techniques:

1.

label.center.x = imageView.center.x

2.

label.centerXAnchor.constraint(equalTo: imageView.centerXAnchor)

What is the difference, if any, between these two methods?

Answer 1

1.Following sets up a label's frame

label.center.x = imageView.center.x

2.Following sets up an auto layout constraint for a label

label.centerXAnchor.constraint(equalTo: imageView.centerXAnchor)

If you are not familiar with an autolayout check an Apple's Auto Layout Guide

Answer 2

When you are referring to center property, you are getting the CGPoint reference of this, it is a low-level way of positioning things in your application. When you are working with centerXAnchor, you are using the Autolayout method to positioning things, as you know Auto Layout dynamically calculates the size and position of all the views in your view hierarchy, based on constraints placed on those views.