Updating

Updating is a property wrapper that reads and stays updated to a value owned by a source of truth.

Use a Updating to create a one-way connection between a property that stores data, and a view that displays the data. An Updating connects a property to a source of truth stored elsewhere, instead of storing data directly, similar to Binding. However, it does not have the ability to write to its source of truth.

Usage

struct MyText: View {
    @Updating var string: String
    var body: some View {
        Text(string)
    }
}

The parent view declares a property to hold the string state, using the State property wrapper to indicate that this property is the value’s source of truth.

struct TextEditingView: View {
    @State private var string: String = "test"
    var body: some View {
        VStack {
            TextField("Enter Text Here", $string)
            MyText(string)
        }
    }
}

When TextEditingView initializes MyText, it passes an Updating of its state property into the button’s Updating property. Whenever the user changes the text, MyText updates its string state. This differs from state, as state only takes the initial value and any updates done in the parent view would not be reflected in the child view.

Adding to a project

Using Swift Package Manager: File -> Add Packages, then input the URL of this github repo

Implementation Details

Updating turns its Value into an autoclosure for () -> Value. In SwiftUI, whenever a value in a closure changes, SwiftUI is forced to re-evaluate the closure, which allows Updating to stay synced with its source of truth.

Usage outside of SwiftUI

Updating works outside of SwiftUI, like in the following example:

var testString: String = "initial"
let updating = Updating(wrappedValue: testString)
testString = "changed!"
print(updating.wrappedValue) // "changed!"

Custom prefix operator

Instead of using self._myValue = Updating(wrappedValue: myValue), you can use self._myValue = <-myValue