Please help me understand when SwiftUI subviews are re-initialized

Question

chrisguthrie OP

Created Sep ’20

Replies 2

Boosts 0

Participants 2

See below playground code:

Code Block swiftimport SwiftUI
import PlaygroundSupport
struct InnerView: View {
  @Binding var text: String
  @State private var startedChange = false
  var body: some View {
    Text("Hello").onAppear {
      if !self.startedChange {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
          self.text = "cat"
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
          self.text = "cheetah"
        }
        self.startedChange = true
      }
    }
  }
}
struct ContentView: View {
  @State private var animalName = "dog"
  var body: some View {
    VStack {
      InnerView(text: $animalName)
      Text(animalName)
    }
  }
}
PlaygroundPage.current.setLiveView(ContentView())

The bottom

Code Block swiftText(animal.name)

alternates irregularly between "cat" and "cheetah," in an infinite loop of race conditions. I expected the text to change to "cat" after one second and then "cheetah" after another.

I would not have expected

Code Block swift   @State private var startedChange = false

to be initialized more than once.

Where is my mental model wrong?

(Xcode 12.0)

Answered by OOPer in 635866022

Generally, it is not clear how Playground is managing SwiftUI view to show it in a live view.

Your code works as you expect in an actual app.
I guess your mental model is not wrong, just that Playground does something more than you expect.

Boost

Answer 1

OOPer OP

Sep ’20

Accepted Answer

Generally, it is not clear how Playground is managing SwiftUI view to show it in a live view.

Your code works as you expect in an actual app.
I guess your mental model is not wrong, just that Playground does something more than you expect.

1

Answer 2

chrisguthrie OP

Sep ’20

Ah, that's fun...

Thanks for the help.

0