---
title: "onGeometryChange(for:of:action:)"
framework: swiftui
role: symbol
role_heading: Instance Method
path: "swiftui/view/ongeometrychange(for:of:action:)"
---

# onGeometryChange(for:of:action:)

Adds an action to be performed when a value, created from a geometry proxy, changes.

## Declaration

```swift
@preconcurrency nonisolated func onGeometryChange<T>(for type: T.Type, of transform: @escaping @Sendable (GeometryProxy) -> T, action: @escaping (T) -> Void) -> some View where T : Equatable, T : Sendable

```

## Parameters

- `type`: The type of value transformed from a doc://com.apple.SwiftUI/documentation/SwiftUI/GeometryProxy.
- `transform`: A closure that transforms a doc://com.apple.SwiftUI/documentation/SwiftUI/GeometryProxy to your type.
- `action`: A closure to run when the transformed data changes.

## Discussion

Discussion The geometry of a view can change frequently, especially if the view is contained within a ScrollView and that scroll view is scrolling. You should avoid updating large parts of your app whenever the scroll geometry changes. To aid in this, you provide two closures to this modifier: transform: This converts a value of GeometryProxy to your own data type. action: This provides the data type you created in of and is called whenever the data type changes. For example, you can use this modifier to know how much of a view is visible on screen. In the following example, the data type you convert to is a Bool and the action is called whenever the Bool changes. ScrollView(.horizontal) {     LazyHStack {          ForEach(videos) { video in              VideoView(video)          }      }  }

struct VideoView: View {     var video: VideoModel

var body: some View {         VideoPlayer(video)             .onGeometryChange(for: Bool.self) { proxy in                 let frame = proxy.frame(in: .scrollView)                 let bounds = proxy.bounds(of: .scrollView) ?? .zero                 let intersection = frame.intersection(                     CGRect(origin: .zero, size: bounds.size))                 let visibleHeight = intersection.size.height                 return (visibleHeight / frame.size.height) > 0.75             } action: { isVisible in                 video.updateAutoplayingState(                     isVisible: isVisible)             }     } } For easily responding to geometry changes of a scroll view, see the onScrollGeometryChange(for:of:action:) modifier.