NEW: Join my free 100 Days of SwiftUI challenge today! >>

What is the @State property wrapper?

Paul Hudson    @twostraws   

Fully updated for Xcode 11.2

SwiftUI uses the @State property wrapper to allow us to modify values inside a struct, which would normally not be allowed because structs are value types. When we put @State before a property, we effectively move its storage out from our struct and into shared storage managed by SwiftUI. This means SwiftUI can destroy and recreate our struct whenever needed (and this can happen a lot!), without losing the state it was storing.

@State should be used with simple struct types such as String and Int, and generally shouldn’t be shared with other views. If you want to share values across views, you should probably use @ObservedObject or @EnvironmentObject instead – both of those will ensure that all views will be refreshed when the data changes.

To re-enforce the local nature of @State properties, Apple recommends you mark them as private, like this:

@State private var username = ""

This isn’t required, but it seems like smart practice.

SPONSORED Instabug helps you identify and resolve severe crashes quickly. You can retrace in-app events and know exactly which line of code caused the crash along with environment details, network logs, repro steps, and the session profiler. Ask more questions or keep users up-to-date with in-app replies straight from your dashboard. Instabug takes data privacy seriously, so no one sees your data but you! See more detailed features comparison and try Instabug's crash reporting SDK for free.

Similar solutions…

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!