How to initialize @Binding in SwiftUI

⋅ 2 min read ⋅ SwiftUI Property Wrapper

Table of Contents

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 {
Toggle("I Accept Terms and Conditions", isOn: $isAccepted)

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

Cannot assign value of type 'Binding<Bool>' to type 'Bool'
Cannot assign value of type 'Binding' to type 'Bool'

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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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.

Read more article about SwiftUI, Property Wrapper, or see all available topic

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