A modifier that provides automatic sizing for sheets in SwiftUI (iOS 16+)

SelfSizingSheetPresentation.swift

import SwiftUI

struct SelfSizingSheetPresentation: ViewModifier {
    private enum BoundsPreference: PreferenceKey {
        static let defaultValue: Anchor<CGRect>? = nil

        static func reduce(value: inout Value, nextValue: () -> Value) {
            value = nextValue()
        }
    }

    @State private var sheetHeight: CGFloat = .zero

    func body(content: Content) -> some View {
        content
            .anchorPreference(
                key: BoundsPreference.self,
                value: .bounds,
                transform: { $0 }
            )
            .overlayPreferenceValue(BoundsPreference.self) { anchor in
                GeometryReader { proxy in
                    if let anchor {
                        Color.clear
                            .onChange(
                                of: proxy[anchor].size.height,
                                initial: true
                            ) { _, newValue in
                                self.sheetHeight = newValue
                            }
                    }
                }
            }
            .presentationDetents([.height(sheetHeight)])
    }
}

extension View {
    func selfSizingSheetPresentation() -> some View {
        modifier(SelfSizingSheetPresentation())
    }
}