Binding value from an ObservableObject

Question

newwbee OP

Created Dec ’19

Replies 3

Boosts 4

Views 23k

Participants 5

Aim:

I have a model which is an

ObservableObject

. It has a

Bool

property, I would like to use this

Bool

property to initialise a

@Binding

variable.

Questions:

How to convert an
```
@ObservableObject
```
to a
```
@Binding
```
?
Is creating a
```
@State
```
the only way to initialise a
```
@Binding
```
?

Note:

I do understand I can make use of
```
@ObservedObject
```
/
```
@EnvironmentObject
```
, and I see it's usefulness, but I am not sure a simple button needs to have access to the entire model.
Or is my understanding incorrect ?

Code:

import SwiftUI
import Combine
import SwiftUI
import PlaygroundSupport

class Car : ObservableObject {

  @Published var isReadyForSale = true
}

struct SaleButton : View {

  @Binding var isOn : Bool

  var body: some View {

  Button(action: {

  self.isOn.toggle()
  }) {
  Text(isOn ? "On" : "Off")
  }
  }
}


let car = Car()

//How to convert an ObservableObject to a Binding
//Is creating an ObservedObject or EnvironmentObject the only way to handle a Observable Object ?

let button = SaleButton(isOn: car.isReadyForSale) //Throws a compilation error and rightly so, but how to pass it as a Binding variable ?

PlaygroundPage.current.setLiveView(button)

Answered by Jim Dovey in 397773022

ObservableObject will provide you with a binding to any contained property automatically via the $-prefix syntax:

class Car: ObservableObject {
    @Published var isReadyForSale = true
}

struct SaleView: View {
    @Binding var isOn: Bool

    var body: some View {
        Toggle("Ready for Sale", isOn: $isOn)
    }
}

struct ContentView: View {
    @ObservedObject var car: Car

    var body: some View {
        Text("Details")
            .font(.headline)
        SaleView(isOn: $car.isReadyForSale)  // generates a Binding to 'isReadyForSale' property
    }
}

Boost

Answer 1

newwbee OP

Dec ’19

Binding has an initializer which accepts getter and setter closures.

We can use the getter and setter to access and update the model.

let button = SaleButton(isOn: Binding(get: {car.isReadyForSale}, set: { car.isReadyForSale = $0 }))

Refer: https://developer.apple.com/documentation/swiftui/binding/3363053-init

4

Answer 2

Jim Dovey OP

Dec ’19

Accepted Answer

ObservableObject will provide you with a binding to any contained property automatically via the $-prefix syntax:

class Car: ObservableObject {
    @Published var isReadyForSale = true
}

struct SaleView: View {
    @Binding var isOn: Bool

    var body: some View {
        Toggle("Ready for Sale", isOn: $isOn)
    }
}

struct ContentView: View {
    @ObservedObject var car: Car

    var body: some View {
        Text("Details")
            .font(.headline)
        SaleView(isOn: $car.isReadyForSale)  // generates a Binding to 'isReadyForSale' property
    }
}

24

Answer 3

coucoseth OP

Jun ’22

how can you bind a function

0