OnAppear only once the view is opened

Question

I want to update the view with data when a view is opened so I added:

.onAppear {
    loadData()
}

But I only want to update it once when the view gets opened not every time it gets reopened e.g. with a back button.

--> Only update on App start

Add a property to keep track off if it has been loaded yet or if the data loaded is already present? — Joakim Danielson, Sep 30 '22 at 17:02
My goal is something like 'if firstTimeOpened { .onAppear { code... — Social Processing, Sep 30 '22 at 17:05
It won't work with a property to keep track because the data gets stored in different CoreData entities and it can't be verified if the data is already up to date — Social Processing, Sep 30 '22 at 17:07
you were saying `loadData` is getting called each time view appears if you just one to do it once add one bool property to maintain state that data is loaded or not — Nirav D, Sep 30 '22 at 17:09
If you can't verify that the data is up to date then don't you need to reload it anyway each time the view appears? — Joakim Danielson, Sep 30 '22 at 17:17
No because it is daily API data and it doesn't make sense to update it every 2 minutes when clicking through views — Social Processing, Sep 30 '22 at 17:19
Keep track of appear time in your model then each time appear called check to see for how long it is since last appear. — Ptit Xav, Sep 30 '22 at 18:44
Does this answer your question? [Initialize app with an Async function | SwiftUI](https://stackoverflow.com/questions/68668770/initialize-app-with-an-async-function-swiftui) — lorem ipsum, Sep 30 '22 at 19:21

azamsharp · Answer 1 · 2022-10-01T15:24:01.997

0

You can put the value in UserDefaults so you will know in the second load that you have already performed loading.

extension UserDefaults {
    
    var firstTimeVisit: Bool {
        get {
            return UserDefaults.standard.value(forKey: "firstTimeVisit") as? Bool ?? true
        } set {
            UserDefaults.standard.setValue(newValue, forKey: "firstTimeVisit")
        }
    }
    
}

struct ContentView: View {
    
    var body: some View {
        VStack {
            
        }.task {
            if UserDefaults.standard.firstTimeVisit {
                // load Data
                UserDefaults.standard.firstTimeVisit = false
            } 
        }
    }
}

UPDATE:

extension UserDefaults {
    
    var firstTimeVisit: Bool {
        get {
            return !UserDefaults.standard.bool(forKey: "firstTimeVisit")
        } set {
            
            UserDefaults.standard.set(newValue, forKey: "firstTimeVisit")
        }
    }
    
}

edited Oct 01 '22 at 15:24

answered Oct 01 '22 at 02:28

azamsharp

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Please do not suggest KVC with `UserDefaults`. There is `bool(forKey:` and `set(_:forKey:`) – vadian Oct 01 '22 at 07:35
Good morning, I‘m new in swift. Why is KVC not good or what is the alternative to @azamsharp‘s code? – Social Processing Oct 01 '22 at 09:29
@SocialProcessing vadian mentioned that in his comment. Note that this solution will set the property once and store it so next time the app is started nothing will be downloaded so you will need some logic to handle that as well in case it’s a new day. – Joakim Danielson Oct 01 '22 at 09:55

OnAppear only once the view is opened

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