Rest APIs and SwiftUI

I recently had someone ask me how I handled fetching and rendering data from a REST API in a SwiftUI view.

If you’re coming from something like React, it’s actually handled differently. We can’t just fire off a request in init or onAppear, and update some @State. Awkwardness with escaping closures, structs not being mutable, etc etc etc.

Luckily SwiftUI has some constructs that can help :) I won’t be going over how to make GET requests or whatever in detail, though I like to use Just.

Firsts up, let’s have a view

struct UserProfile: View {
    @ObservedObject user: User = User(username: "elm", name: "Ellie")

    var body: some View {
    	VStack {
        	Text("Username: \(self.user.username)")
        	Text("Name: \(self.user.name)")
        }
    }
}

So, how do we get the user object here loaded? @State?

Actually no. There’s something called an ObservableObject. This is an object with @Published properties. If a @Published property is updated, any view containing this object will have an update triggered.

An example will probably illustrate this more effectively

struct User: ObservableObject {
    @Published var username: String
    @Published var name: String

    init(username: String, name: String) {
    	self.username = username
        self.name = name
        
        self.load()
    }
    
    func load() {
    	somehowRequestDataAsynchronously();
        // so basically just change `username` or `name` in here
    }
}

The view essentially “observes” something “observable” - @ObservedObject and @ObservableObject. As soon as a @Published property is updated on something we are observing, a re-render is triggered and the view updates!

Hopefully this clears things up!