SwiftUI - Invert a boolean binding

Question

I have a Binding<Bool> binding in a swiftUI view. Something along the lines of:

struct MyCoolView: View { 
    @ObservedObject var viewModel: ViewModel

    var body: some View { 
        Text("Here is a cool Text!").sheet(isPresented: $viewModel.MyProperty) { 
            SomeModalView()}
        }
}

I want the isPresented to use the opposite boolean value of what is stored in the property using Boolean negation, the exclamation point ! operator, or some other method.

Swift wont let me just do something like

.sheet(isPresented: !$viewModel.MyProperty)

!$viewModel gives the error:

Cannot convert value of type 'Bool' to expected argument type 'Binding<Bool>'

Any thoughts on how to deal with this?

Could you just not invert it already in a the viewModel before it get sent to the view? Or am I missing something? — Aecasorg, Apr 30 '21 at 08:47
I should update and say that with about a year and a half of hindsight and a better sense of how to properly use Combine and publishers what you suggest is indeed the correct way to do it. The way I'd approach this now is to create a subscription to the Boolean inside the view model that is stored inside another published variable. I suppose time makes fools of us all on SO. — snarik, May 20 '21 at 18:48

tgebarowski · Answer 1 · 2020-08-31T20:57:30.240

57

What about creating a custom prefix operator?

prefix func ! (value: Binding<Bool>) -> Binding<Bool> {
    Binding<Bool>(
        get: { !value.wrappedValue },
        set: { value.wrappedValue = !$0 }
    )
}

Then you could run your code without any modification:

.sheet(isPresented: !$viewModel.MyProperty)

If you don't like operators you could create an extension on Binding type:

extension Binding where Value == Bool {
    var not: Binding<Value> {
        Binding<Value>(
            get: { !self.wrappedValue },
            set: { self.wrappedValue = !$0 }
        )
    }
}

and later do something like:

.sheet(isPresented: $viewModel.MyProperty.not)

or even experiment with a global not function:

func not(_ value: Binding<Bool>) -> Binding<Bool> {
    Binding<Bool>(
        get: { !value.wrappedValue },
        set: { value.wrappedValue = !$0 }
    )
}

and use it like that:

.sheet(isPresented: not($viewModel.MyProperty))

edited Aug 31 '20 at 20:57

answered May 11 '20 at 15:17

tgebarowski

1,189
11
14

You mean `b in self.wrappedValue = !b`, right? Other than that nice answer :) – Dávid Pásztor May 22 '20 at 14:08
1

Actually, when I negate in setter and getter I will have the same result (without negation). So we should either negate in getter or setter not in two places. Probably negating in the setter is more straightforward though. – tgebarowski May 22 '20 at 15:08
Nope, your code actually produces flipped results when you use the setter. If you input `true` to the setter, it will set the `value.wrappedValue` to `true` instead of setting the value of the negated binding to `true`. Try setting `returnedBinding.wrappedValue = true` where `returnedBinding` is the output of your `!anotherBinding` operator and you'll see that if you call `returnedBinding.wrappedValue` straight after, it will return `false` instead of `true`. – Dávid Pásztor May 22 '20 at 15:38
@tgebarowski very nice extensions and functions, but need a little fix. You should reverse the value on set, like `set: { value.wrappedValue = !$0 }` – alemorgado Aug 26 '20 at 12:38
extension is perfect – Lukasz D Oct 30 '21 at 19:27
The extension is such an elegant solution, thank you so much! – Michel Storms Jan 04 '23 at 09:35
@tgebarowski go wrong if put prefix operate into swift package, see https://stackoverflow.com/questions/75808263/problem-using-prefix-operator-from-framework – foolbear Mar 22 '23 at 13:43

score 34 · Accepted Answer · answered Dec 24 '19 at 23:38

34

You can build a binding by yourself:

Text("Here is a cool Text!").sheet(isPresented:
         Binding<Bool>(get: {return !self.viewModel.MyProperty},
                       set: { p in self.viewModel.MyProperty = p})
          { SomeModalView()} }

answered Dec 24 '19 at 23:38

E.Coms

11,065
2
23
35

5

Small correction: add `!` in `set`. I.e., `self.viewModel.MyProperty = !p`. – Yonat Dec 25 '19 at 11:53

Cloud · Answer 3 · 2020-07-13T15:39:37.897

9

Based off @E.Com's answer, here is a shorter way to construct a Binding<Bool>:

Binding<Bool>(
    get: { !yourBindingBool },
    set: { yourBindingBool = !$0 }
)

edited Jul 13 '20 at 15:39

answered Jul 13 '20 at 15:30

Cloud

938
1
8
24

score 4 · Answer 4 · answered Sep 08 '20 at 11:17

4

Add extension like so:

extension Binding where Value == Bool {
    func negate() -> Bool {
        return !(self.wrappedValue)
    }
}

answered Sep 08 '20 at 11:17

Mihkel L.

1,543
1
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SwiftUI - Invert a boolean binding

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