How we can run some logic stand alone from Views before SwiftUI start rendering ContentView?

Question

I want to know how I can run some logic func or control flow operator before SwiftUI attempt to render ContentView? where and how I can put my codes?

Updated: init(){} before var body: some Scene

When I use init and do my logic there I cannot find a way to report my results of process, how I can solve this issue?

my code:

    import SwiftUI

@main
struct _99App: App
{
    init() {
        let firstName = "omid"
        print(firstName)
    }
    
    @State var name : String = firstName // ← Here        Error: Cannot find 'firstName' in scope
    
    
    var body: some Scene {

        WindowGroup {
            
            ContentView(name: $name)
                
        }
 
        
        
    }
}

PS: basically I need a place to run my logic before any thing happens in app.

Does this answer your question stackoverflow.com/a/63525968/12299030? — Asperi
– Asperi, Commented Nov 4, 2020 at 10:14

Asperi · Accepted Answer · 2020-11-04 14:03:05Z

2

You can use some kind of ObservableObject as StateObject which will be initialised before everything else.

So the solution might look like following

let globalState = MyAppState()

@main
struct _99App: App
{
    @StateObject var appState = globalState
    
    init() {
       globalState.firstName = "updated"
        print("updated")
    }

    var body: some Scene {
        WindowGroup {
            ContentView().environmentObject(appState)
            // and use as
            // @EnvironmentObject var appState: MyAppState
            // inside ContentView
        }
    }
}

class MyAppState: ObservableObject {
    @Published var firstName: String
    
    init() {
        self.firstName = "omid"
        print(firstName)
    }
}

edited Nov 4, 2020 at 14:03

answered Nov 4, 2020 at 11:21

Asperi

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1 Comment

swiftPunk Over a year ago

if you put this code init() { print("⌘") } *** before ***var body: some Scene you would see it runs faster than MyAppState-Class, run time of MyAppState is almost the same as ContentView, in the fact they are happing at the same time, like domino, but I want first position of code running in app! as you will see the sign of ⌘ would be printed always first and way faster than print(firstName) and I want get that place for my logic.

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