Most efficient way to call a function upon variable state change

Question

marcofusco111 OP

Created Jul ’24

Replies 2

Boosts 0

Participants 2

Hi,

I have a button view that is used in many different ways in an app that I'm working on. One of the ways it is used is in an account creation form. Since the button is in a child view, the action: { } button function isn't available in the view where the input field variables are. I could import the class with the function to the button view but I don't want to pass the input field variables into the button view. I tried binding a boolean variable to the button view and checked for it's state change in the parent view using .onChange(), but the use case for that I found was depreciated and I'm unable to revert the state of the variable in the .onChange function.

To reiterate, in a main view, I need to call a function in a given class and pass variables to it, upon a button being pressed in a child view. Any help would be greatly appreciated.

Answered by Claude31 in 796321022

It would be much simpler to explain if you posted the code you have tried with Binding.

Is it what you are looking for ?

struct TestButton: View {
    
    @Binding var isSelected: Bool
    
    var body: some View {
        Button(action: {
            self.isSelected.toggle()
        }) {
            Text("Change")
        }
    }
}

struct ContentView: View {
    
    @State var buttonState = false
    @State var someTextToDisplay = "no state defined yet"
    
    func forStateOn() {
        someTextToDisplay = "State is on"
    }

    func forStateOff() {
        someTextToDisplay = "State is off"
    }

    var body: some View {
        VStack {
            Text(buttonState ? "selected" : "unselected")
            TestButton(isSelected: $buttonState)
            Text(someTextToDisplay)
        }
        .onChange(of: buttonState) { oldState, newState in
            if newState {
                forStateOn()
            } else {
                forStateOff()
            }
        }
    }
}

Boost

Answer 1

Claude31 OP

Jul ’24

Accepted Answer

It would be much simpler to explain if you posted the code you have tried with Binding.

Is it what you are looking for ?

struct TestButton: View {
    
    @Binding var isSelected: Bool
    
    var body: some View {
        Button(action: {
            self.isSelected.toggle()
        }) {
            Text("Change")
        }
    }
}

struct ContentView: View {
    
    @State var buttonState = false
    @State var someTextToDisplay = "no state defined yet"
    
    func forStateOn() {
        someTextToDisplay = "State is on"
    }

    func forStateOff() {
        someTextToDisplay = "State is off"
    }

    var body: some View {
        VStack {
            Text(buttonState ? "selected" : "unselected")
            TestButton(isSelected: $buttonState)
            Text(someTextToDisplay)
        }
        .onChange(of: buttonState) { oldState, newState in
            if newState {
                forStateOn()
            } else {
                forStateOff()
            }
        }
    }
}

0

Answer 2

marcofusco111 OP

Jul ’24

Hi,

I have a follow up question. In an older project, using that code, I get an error: 'onChange(of:initial:_:)' is only available in iOS 17.0 or newer

The solution provided is to wrap the code in if #available(iOS 17.0, *) { }, but I'm only able to wrap the whole view inside of it, like so:


if #available(iOS 17.0, *) {

    VStack () {
         // view with .onChange
    }

} else {
    VStack () {
         // view with older solution
    }
}

The view is quite lengthy so it would be very redundant to have the same view twice, (the same view for each component of the if/else statement). Is there a way to implement an if statement so that I would only need the code for the view once (something like the code below)?

VStack {

}
if #available(iOS 17.0, *) {
    .onChange() {

    }
} else {
    // older solution
}

0