How to implement protocols and delegates in SwiftUI

Question

I was converting one of my swift project into SwiftUI. I need to convert delegtes and protocols to SwiftUI, is it allowed in SwiftUI? or any alternative methods are there? Please help me i'm so confused in SwiftUI.

I'm calling a delegate method from one of my class, then delegate method will be present in another ViewController.

//PresenterClass

protocol SplashPresenterDelegate {
    func didFetchedSystemInfo(info: String)
}
class SplashPresenter: NSObject {
    var delegate: SplashPresenterDelegate?

    func getSystemInfo(){
         self.delegate?.didFetchedSystemInfo(info: "ResponseString") 
    }
}


// Viewcontroller class

class myViewController: UIViewController {
   .
   .
   .
}

extension  myViewController: SplashPresenterDelegate{
   func didFetchedSystemInfo(info: String){
      print("delegate called")
   } 
}

Please help me to convert this code to SwiftUI

Protocols are a core part of the swift language and is of course allowed when using SwiftUI. Delegate is a design pattern that also can be used anytime but it is not part of SwiftUI while it was well used in UIKit. Most likely you would want to use a property wrapper here like @State — Joakim Danielson
– Joakim Danielson, Commented Aug 5, 2020 at 7:24
@JoakimDanielson i have updated my question with code, can you please give a solution? — Jan49
– Jan49, Commented Aug 5, 2020 at 7:26
The SplashPresenter/Delegate can be used in SwiftUI code as-is. Show your SwiftUI code where you need that presenter. — Asperi
– Asperi, Commented Aug 5, 2020 at 7:27
@Asperi i want to convert my MyViewcontroller extension to swiftUI to get delegate from splashpresenter — Jan49
– Jan49, Commented Aug 5, 2020 at 7:28
You can take closures as parameters in your ViewRepresentables to satisfy related delegate methods. — Enes Karaosman
– Enes Karaosman, Commented Aug 5, 2020 at 9:55

mginn · Accepted Answer · 2020-08-05 16:21:59Z

5

Typically, SwiftUI prefers the pattern of taking callbacks rather than protocol/delegates. For instance, each button in an ActionSheet has a closure that is executed when the button is tapped.

You shouldn't just convert your code over directly, though. SwiftUI, being declarative, uses different paradigms for a lot of things. For instance, you wouldn't have a didFetchInfo method, you would just assign it to a @Published variable.

Think about having "single sources of truth", where a single variable is always correct. For example, List simply takes an array and updates when the array changes, unlike UITableView where you provide the data through numberOfRows and cellForRowAt. I don't know enough about your specific project to give more detail, but those are things to think about.

answered Aug 5, 2020 at 16:21

mginn

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