How to get child view size in SwiftUI View

GetChildViewSize.swift

import SwiftUI

struct ContentView: View {
    @State var size: CGSize = .zero

    var body: some View {
        VStack {
            Text(size.debugDescription)
            ChildView()
        }
        .onPreferenceChange(SizePreferenceKey.self) {
            size = $0
        }
    }
}

struct ChildView: View {
    var body: some View {
        Text("Message")
            .background(GeometryReader { geometry in
                Color.clear.preference(
                    key: SizePreferenceKey.self,
                    value: geometry.size
                )
            })
    }
}

struct SizePreferenceKey: PreferenceKey {
    static var defaultValue: CGSize = .zero
    static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
        // If there are if statements in the target view, nextValue() can be (0, 0)
        value = value.width * value.height > nextValue().width * nextValue().height ? value : nextValue()
    }
}