Скачать или смотреть How to Use @ FocusState.Binding with Custom Initializers in SwiftUI

Learn the correct way to pass and initialize @ FocusState.Binding in SwiftUI subviews with custom initializers, avoiding common assignment errors.
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This video is based on the question https://stackoverflow.com/q/79419152/ asked by the user 'Z S' ( https://stackoverflow.com/u/145552/ ) and on the answer https://stackoverflow.com/a/79419233/ provided by the user 'Sweeper' ( https://stackoverflow.com/u/5133585/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When building SwiftUI views, managing focus states across parent and child views is common. The @ FocusState and its @ FocusState.Binding provide a convenient way to bind focus to UI elements.

Passing a @ FocusState binding from a parent to a subview is straightforward unless you use a custom initializer in the subview. This raises a common confusion: how to properly assign @ FocusState.Binding properties within custom initializers.

The Problem

If you declare a subview property with:

[[See Video to Reveal this Text or Code Snippet]]

and try to initialize it in a custom initializer like:

[[See Video to Reveal this Text or Code Snippet]]

You get the error:

Cannot assign value of type 'FocusState ButtonState? .Binding' to type 'ButtonState?'

This happens because bindedFocusButtonState is a computed property for the wrapped value, not the underlying binding itself.

Understanding @ FocusState.Binding Property Wrapper

A declaration like:

[[See Video to Reveal this Text or Code Snippet]]

actually generates three properties:

_bindedFocusButtonState (of type FocusState<ButtonState?>.Binding): the storage for the binding itself.

bindedFocusButtonState (computed): returns or sets wrappedValue of the binding.

$bindedFocusButtonState (computed): returns the projected value (the binding).

Hence, assigning a FocusState.Binding must target the underscore-prefixed property, which stores the binding, not the computed wrapper.

The Correct Solution

Inside your custom initializer, assign the incoming binding to the underscore property:

[[See Video to Reveal this Text or Code Snippet]]

This directly sets the binding variable backing your property wrapper.

Summary

Use the underscore prefix (_propertyName) to access and assign wrapped property wrapper values in initializers.

Remember @ FocusState.Binding var name is a computed property exposing the wrapped value, not the binding.

Pass FocusState<T>.Binding to the underscore property (_name) during initialization.

This approach preserves the benefits of @ FocusState.Binding and enables clean custom initializers without resorting to manual unwrapping or less elegant workarounds.



Example

[[See Video to Reveal this Text or Code Snippet]]

Using this pattern, you integrate focus state management seamlessly with custom initializers in SwiftUI.