How to initialize @Binding in SwiftUI

If you create a SwiftUI View that has a @Binding variable and need to implement a custom initializer for that view, you might get the following error when trying to initialize the @Binding variable.

Cannot assign value of type 'Binding' to type 'Bool'.

Here is an example of a TermAndConditionView view where I show terms and conditions and a toggle to accept them.

struct TermAndConditionView: View {
    let message: String
    @Binding var isAccepted: Bool
    
    init(message: String, isAccepted: Binding<Bool>) {
        self.message = message
        // 1
        self.isAccepted = isAccepted
    }

    var body: some View {
        VStack {
            Text(message)
            Toggle("I Accept Terms and Conditions", isOn: $isAccepted)
        }
    }
}

1 You will get the error when you try to initialize a @Binding variable like this.

How to initialize @Binding in SwiftUI

@Binding is a Property Wrapper. You can think of it as a getter and setter of an underlying storage.

By default, the compiler synthesizes storage for the instance of the property wrapper by prefixing the name with an underscore (_).

So, if we have a property wrapper named @Binding var isAccepted: Bool, the compiler will synthesize the storage with the name _isAccepted. And the storage type of @Binding is Binding<T>.

In summary

• Binding<Bool> is a type for underlying storage of @Binding.
• This storage is named _isAccepted.
• So to properly initialize it, we directly assign Binding<Bool> to the storage _isAccepted.

init(message: String, isAccepted: Binding<Bool>) {
    self.message = message
    self._isAccepted = isAccepted
}

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Conclusion

The explanation might be confusing if you aren't familiar with the Property Wrapper concept. I encourage you to read more about Property Wrapper here for a better understanding.