Observe Geometry updates on any SwiftUI view

GeometryObserver.swift

import SwifUI

public struct Geometry: Equatable {
    fileprivate var proxy: GeometryProxy?
    public var size: CGSize = .init(width: 10, height: 10)
    public var safeAreaInsets: EdgeInsets = .init()
    
    public func frame(in coordinateSpace: CoordinateSpaceProtocol) -> CGRect {
        proxy?.frame(in: coordinateSpace) ?? .init(origin: .zero, size: size)
    }
    
    public func bounds(of coordinateSpace: NamedCoordinateSpace) -> CGRect {
        proxy?.bounds(of: coordinateSpace) ?? .init(origin: .zero, size: size)
    }
    
    public static func == (lhs: Self, rhs: Self) -> Bool {
        lhs.size == rhs.size
        && lhs.safeAreaInsets == rhs.safeAreaInsets
    }
}

public extension View {
    func onGeometryChange(perform handler: @escaping (Geometry) -> Void) -> some View {
        overlay {
            GeometryReader { geo in
                Color.clear
                    .preference(key: GeometryPreferenceKey.self, value: Geometry(
                        proxy: geo,
                        size: geo.size,
                        safeAreaInsets: geo.safeAreaInsets
                    ))
            }
        }
        .onPreferenceChange(GeometryPreferenceKey.self) { geo in
            handler(geo)
        }
    }
}

private struct GeometryPreferenceKey: PreferenceKey {
    static var defaultValue: Geometry = .init()
    static func reduce(value: inout Geometry, nextValue: () -> Geometry) {
        value = nextValue()
    }
}

Demo:

import SwiftUI

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ContentView: View {
    @State private var showText: Bool = true
    
    var body: some View {
        VStack(spacing: 20) {
            Toggle("Toggle", isOn: $showText.animation())
            
            VStack {
                Image(systemName: "globe")
                    .imageScale(.large)
                    .foregroundColor(.accentColor)
                if showText {
                    Text("Hello, world!")
                }
            }
        }
        .padding()
        .onGeometryChange { geo in
            print(geo.size)           // <—— Toggle the text to see size updates trigger this
        }
    }
}