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How to run some code when state changes using onChange()

Paul Hudson    @twostraws   

Updated for Xcode 12.0

New in iOS 14

SwiftUI lets us attach an onChange() modifier to any view, which will run code of our choosing when some state changes in our program. This is important, because we can’t use property observers like didSet with something like @State.

For example, this will print name changes as they are typed:

struct ContentView : View {
    @State private var name = ""

    var body: some View {
        TextField("Enter your name:", text: $name)
            .textFieldStyle(RoundedBorderTextFieldStyle())
            .onChange(of: name) { newValue in
                print("Name changed to \(name)!")
            }
    }
}
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