---
title: ContainerValueKey
framework: swiftui
role: symbol
role_heading: Protocol
path: swiftui/containervaluekey
---

# ContainerValueKey

A key for accessing container values.

## Declaration

```swift
protocol ContainerValueKey
```

## Overview

Overview You can create custom container values by extending the ContainerValues structure with new properties. First declare a new container value key type and specify a value for the required defaultValue property: private struct MyContainerValueKey: ContainerValueKey {     static let defaultValue: String = "Default value" } The Swift compiler automatically infers the associated Value type as the type you specify for the default value. Then use the key to define a new container value property: extension ContainerValues {     var myCustomValue: String {         get { self[MyContainerValueKey.self] }         set { self[MyContainerValueKey.self] = newValue }     } } Clients of your container value never use the key directly. Instead, they use the key path of your custom container value property. To set the container value for a view, add the containerValue(_:_:) view modifier to that view: MyView()     .containerValue(\.myCustomValue, "Another string") As a convenience, you can also define a dedicated view modifier to apply this container value: extension View {     func myCustomValue(_ myCustomValue: String) -> some View {         containerValue(\.myCustomValue, myCustomValue) } This improves clarity at the call site: MyView()     .myCustomValue("Another string") To read the container value, use Group(subviews:) on a containing view, and then access the container value on members of that collection. @ContentBuilder var content: some View {     Text("A").myCustomValue("Hello")     Text("B").myCustomValue("World") }

Group(subviews: content) { subviews in     ForEach(subviews) { subview in         Text(subview.containerValues.myCustomValue)     } } In practice, this will mostly be used by views that contain multiple other views to extract information from their subviews. You could turn the example above into such a container view as follows: struct MyContainer<Content: View>: View {     var content: Content

init(@ContentBuilder content: () -> Content) {         self.content = content()     }

var body: some View {         Group(subviews: content) { subviews in             ForEach(subviews) { subview in                 // Display each view side-by-side with its custom value.                 HStack {                     subview                     Text(subview.containerValues.myCustomValue)                 }             }         }     } }

## Topics

### Associated Types

- [Value](swiftui/containervaluekey/value.md)

### Type Properties

- [defaultValue](swiftui/containervaluekey/defaultvalue.md)

## See Also

### Accessing a container’s subviews

- [Subview](swiftui/subview.md)
- [SubviewsCollection](swiftui/subviewscollection.md)
- [SubviewsCollectionSlice](swiftui/subviewscollectionslice.md)
- [containerValue(_:_:)](swiftui/view/containervalue(_:_:).md)
- [ContainerValues](swiftui/containervalues.md)