SwiftUI @Binding update doesn't refresh view

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I feel like I'm missing something very basic, but this example SwiftUI code will not modify the view (despite the Binding updating) when the button is clicked

Tutorials I have read suggest this is the correct way to use a binding and the view should refresh automatically

import SwiftUI

struct ContentView: View {
    @Binding var isSelected: Bool

    var body: some View {
        Button(action: {
            self.isSelected.toggle()
        }) {
            Text(isSelected ? "Selected" : "Not Selected")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    @State static var selected: Bool = false

    static var previews: some View {
        ContentView(isSelected: $selected)
    }
}

In the top Level of SwiftUI, @Binding cannot refresh View hierarchy unless manually adding a @state or other refreshing triggers.

          struct ContentView: View {
        @Binding var isSelected : Bool
        @State var hiddenTrigger = false

        var body: some View {
            VStack{
            Text("\(hiddenTrigger ? "" : "")")
            Button(action: {
                self.isSelected.toggle()
                self.hiddenTrigger = self.isSelected
            }) {
                Text(self.isSelected? "Selected" : "not Selected")
            }
            }
        }
    }

    struct ContentView_Previews: PreviewProvider {

        static var selected: Bool = false

        static var previews: some View {
            ContentView(isSelected: Binding<Bool>(get: {selected}, set: { newValue in
                selected = newValue}))
        }
    }

Why is my child SwiftUI view not updating?, Then SwiftUI goes to use these new values to patch up the real UI types prefix to get a binding to the state variable) and 16 (declare the property using the In this case, we are updating the view state through a binding, but the effect is the same. We need to delay the update until the body has been computed. We do so, using the DispatchQueue.main.async trick. If you want to learn more about geometry effect, check my other article: Advanced SwiftUI Animations.

SwiftUI View affects @Binding. @State affects SwiftUI View. @State var affects the view, but to affect another @State it must be used as binding by adding leading $ to value name and it works only inside SwiftUI.

To trigger SwiftUI change from outside, i.e. to deliver/update Image, use Publisher that looks like this:

// Declare publisher in Swift (outside SwiftUI)    
public let imagePublisher = PassthroughSubject<Image, Never>()

// And within SwiftUI it must be handled:
struct ContentView: View {
// declare @State that updates View:
    @State var image: Image = Image(systemName: "photo")
    var body: some View {
// Use @State image declaration
                image
// Subscribe this value to publisher "imagePublisher"
                    .onReceive(imagePublisher, perform: { (output: Image) in
// Whenever publisher sends new value, old one to be replaced
                        self.image = output
                    })
    }
}

// And this is how to send value to update SwiftUI from Swift:
imagePublisher.send(Image(systemName: "photo"))

Binding update not triggering UI Change? : SwiftUI, After I write a simple text into it, "Hi" simply doesn't show up. It's like it can't see that searchQuery is different than an empty String. If you change the Binding to� Overview. Use a binding to create a two-way connection between a property that stores data, and a view that displays and changes the data. A binding connects a property to a source of truth stored elsewhere, instead of storing data directly.

SwiftUI Bindings, mutate in your example code), then the object changes and the view updates. But if you push a second PushedView , now it doesn't work. I don't� After almost a year since SwiftUI was released, I decided to give it a go. I started to get my hands dirty by implementing basic UI controls (like Slider or TextField) and how to manipulate view states. In short time, I faced the challenge to update a @State variable based on another @State variable changes.

Looking into this some more I think I understand what's happening.

In this instance I want to use @Binding as I'm building a custom control (like SwiftUI's native Toggle, which also binds to a Bool)

The issue is that the static state in ContentView_Previews (i.e., the line @State static var selected: Bool = false) does not trigger a re-render of the preview when the state changes, so even though the selected state has changed due to interaction with the control, the control (a child of ContentView_Previews) does not re-render itself

This makes it tough to test controls in isolation in the SwiftUI preview, however moving the state into a dummy ObservableObject instance functions correctly. Here's the code:

import SwiftUI
import Combine

class SomeData: ObservableObject {
    @Published var isOn: Bool = false
}

struct MyButton: View {
    @Binding var isSelected: Bool

    var body: some View {
        Button(action: {
            self.isSelected.toggle()
        }) {
            Text(isSelected ? "Selected" : "Not Selected")
        }
    }
}

struct ContentView: View {
    @EnvironmentObject var data: SomeData

    var body: some View {
        MyButton(isSelected: $data.isOn)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView().environmentObject(SomeData())
    }
}

It seems that a change in @State static var doesn't trigger a preview re-render. In the above code my @Binding example is moved into MyButton and the content view's dummy environment instance is bounds to its isSelected property. Tapping the button updates the view as expected in the SwiftUI preview.

7. Understanding State and Binding � Mastering SwiftUI Book, When the state changes, SwiftUI will recompute those views and update the application's appearance. Doesn't it sound great? Or are you a bit confused with � Now, if the view doesn't update when something else does . Controller.message = "new value", then that is expected behavior. String in swift is a value type, so your textValue property is taking a copy of the value, and SwiftUI is monitoring that copy, not the actual value in Controller.message

What is the @Binding property wrapper?, @Binding is one of SwiftUI's less used property wrappers, but it's still hugely important: it lets us declare that one value actually comes from� OK, now let’s look at the binding itself. As you should be able to figure out from the way we used it, the basic initializer for a Binding looks like this: init(get: @escaping -> Value, set: @escaping (Value) -> Void) You can find that by press Cmd+Shift+O and looking up “Binding” in the generated interface for SwiftUI.

How to Modify States During View Updates in SwiftUI, SwiftUI doesn't provide an out-of-the-box implementation for value to the Binding property, which updates the SwiftUI ProgressBar . But the� SwiftUI doesn’t replace UIKit — like Swift and Objective-C, you can use both in the same app. The SwiftUI APIs are consistent across platforms, so it will be easier to develop the same-ish app on multiple platforms using the same source code on each.

3 Ways to React to @State Changes in SwiftUI, Almost a year after SwiftUI was released, I decided to give it a go. of onChange in SwiftUI controls to update other @State variables. like this method, as it doesn't look clean to declare bindings and have business inside� @Binding is one of SwiftUI’s less used property wrappers, but it’s still hugely important: it lets us declare that one value actually comes from elsewhere, and should be shared in both places. This is not the same as @ObservedObject or @EnvironmentObject , both of which are designed for reference types to be shared across potentially many

Comments
  • not sure but try this maybe work $isSelected.wrappedValue
  • Thank you, this is the behaviour I was misunderstanding. I didn't realise that binding to a global variable (via custom get/set closures) or binding to a static @State would not refresh the view hierarchy
  • Your code was exactly was I was looking for. I didn't know how to have a @State property subscribe to a publisher. Thanks :D
  • Thank you for the explanation. How does something like Toggle work, which accepts a Binding<Bool> — is the toggle then unable to set the value for the Binding? My aim is to build a control can manipulate an externally bound value.