SwiftUI: ScrollToModifier

ScrollToModifier.swift

import SwiftUI

public struct ScrollToModifier<T: Hashable>: ViewModifier {
    @Binding var id: T?
    public func body(content: Content) -> some View {
        ScrollViewReader { proxy in
            content
                .onChange(of: id) { newValue in
                    if let id {
                        scrollTo(id: id, using: proxy)
                    }
                }
                .onAppear {
                    if let id {
                        // allow time to draw contents first (otherwise scroll position can fail)
                        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(500)) {
                            scrollTo(id: id, using: proxy)
                        }
                    }
                }
        }
    }

    private func scrollTo(id: T, using proxy: ScrollViewProxy) {
        withAnimation {
            proxy.scrollTo(id, anchor: .top)
            self.id = nil
        }
    }
}

public extension View {

    /// Automatically adds support for scrolling to the view matching the `id` provided by the given binding.
    ///
    /// When the binding has an initial value the modified view will automatically scroll to the view with that id when it first appears.
    /// While the view is presented any change to the binding also makes the scroll move to the new id position.
    ///
    /// The binding is automatically set to `nil` once the scroll has been performed.
    ///
    /// **Note** that the modified view must be part of a ScrollView or List in order to support scrolling. This modifier does not add any scroll, it just reads from its ScrollViewProxy and updates it accordingly.
    /// - Parameter id: A binding property to the id used to identify the view.
    /// - Returns:
    func scrollTo<T: Hashable>(id: Binding<T?>) -> some View {
        modifier(ScrollToModifier(id: id))
    }
}