didSet let us attach observers to properties, meaning that Swift will run some code when they change so that we have a chance to respond to the change. The question is: do you want to know before the property changes, or after?
The simple answer is this: most of the time you will be using
didSet, because we want to take action after the chance has happened so we can update our user interface, save changes, or whatever. That doesn’t mean
willSet isn’t useful, it’s just that in practice it is significantly less popular than its counterpart.
The most common time
willSet is used is when you need to know the state of your program before a change is made. For example, SwiftUI uses
willSet in some places to handle animations so that it can take a snapshot of the user interface before a change. When it has both the “before” and “after” snapshot, it can compare the two to see all the parts of the user interface that need to be updated.
SPONSORED Are you tired of wasting time debugging your Swift app? Instabug’s SDK is here to help you minimize debugging time by providing you with complete device details, network logs, and reproduction steps with every bug report. All data is attached automatically, and it only takes a line of code to setup. Start your free trial now and get 3 months off exclusively for the Hacking with Swift Community.
Link copied to your pasteboard.