MainThreadPropertyAccessor

Syntactic sugar for setting properties on an ObservableObject on the main thread from within a Task.

Task {
    self.setOnMain.status = "Now I'll never get purple warnings again!"
}

Installation

You can use the Swift Package Manager by declaring MainThreadPropertyAccessor as a dependency in your Package.swift file:

.package(url: "https://github.com/theisegeberg/MainThreadPropertyAccessor", from: "0.1.0")

For more information, see the Swift Package Manager documentation.

The problem

ObservableObject is often used as a kind of controller for SwiftUI View. After structured concurrency (async/await) was introduced we'll often need to set the value of a @Published property inside of a ObservableObject. This means wrapping the code in DispatchQueue.main.async { ... } or using a @MainActor annotated method. This can be done, but it's a lot of code.

The solution

A protocol with no requirements that provides a default extension that exposes only one computed property: .setOnMain. This returns an object that can be subscripted into based on the KeyPath's of the ObservableObject that implements the protocol.

Usage

Add the protocol MainThreadPropertyAccessor to your ObservableObject
Use self.setOnMain.somePropertyOfYourObject = newValue to set properties on your ObservableObject

class AnObservableObject: ObservableObject, MainThreadPropertyAccessor {
    @Published var status:String = ""
    func updateStatus() {
        Task {
            // Do some async work
            self.status = "Will update the UI from a background thread" // Warning!
            self.setOnMain.status = "Will update the UI from the main dispatch queue" // 😘
        }
    }
}