This is a simple project that shows how to implement Swift UI bindings for computed properties.
This is slightly difficult because the @State property wrapper can't be applied to computed properties.
@State var showErrorAlert: Bool { // Error: Property wrapper cannot be applied to a computed property
return currentState == .showErrorAlert
}
A little googling turned up this question on Stack Overflow:
https://stackoverflow.com/questions/59738550/how-to-bind-a-computed-property-in-swiftui
Which explains how to create Bindings that can do exactly what we need. So, for example, if we need a Binding<Bool> that returns true when our currentState variable has a particular value we can do something like:
.alert("Network Error!", isPresented: Binding<Bool>(
get: { return currentState == .showErrorAlert },
set: { newValue in /* ignore; this binding is effectively read-only */ }
) {
...
}
The example code here shows two different approaches to creating the same View:
NormalView.swift: shows a naive approach, where we have a number of different Bool properties that we use for @State and bindings. This approach is easier, because we can use the standard binding syntax ($var), but it's also error-prone: it would be very easy to forget to update one of the boolean properties and introduce bugs.
ComputedBindingsView.swift: takes the View from NormalView.swift and replaces all of the Bool properties with a single CurrentState enum. It then drives the UI configuration from this enum and creates computed Bool bindings on-the-fly where necessary to make the UI work.