A view modifier that sets the resizing restrictions for the view's window

View+WindowResizingRestrictions.swift

// IMPORTANT: The following code doesn't support specifying a window's 
// minimum and maximum size when used to constrain a window's aspect ratio.
// Please use this newer view modifier extension instead: 
// https://gist.github.com/drewolbrich/03460fc1bb71b9a821fff722f17ec977

//
//  View+WindowResizingRestrictions.swift
//
//  Created by Drew Olbrich on 11/19/23.
//

import SwiftUI

extension View {
    
    /// Sets the resizing restrictions for the view's window.
    ///
    /// The `resizingRestrictions` parameter may have one of the following values:
    ///
    /// - **none**: Do not display the window's resize handle when the user gazes at the window's lower left and right corners. The window will not be resizable.
    /// - **uniform**: Allow the user to resize the window, but constrain the window's aspect ratio to match the values passed to the containing window group's `defaultSize` view modifier.
    /// - **freeform**: Allow the user to freely resize the window. This is the default behavior.
    ///
    /// This view modifier was written for visionOS 1.0 beta 6, and may or may not work
    /// as expected in future visionOS beta releases.
    ///
    /// ## Example Usage
    ///
    /// ```
    /// WindowGroup {
    ///     MyView()
    ///         // Do not display the window's resize handle.
    ///         .windowResizingRestrictions(.none)
    /// }
    /// .defaultSize(width: 600, height: 400)
    ///
    /// WindowGroup {
    ///     MyView()
    ///         // Constrain the window's size to a fixed aspect ratio.
    ///         .windowResizingRestrictions(.uniform)
    /// }
    /// .defaultSize(width: 500, height: 500)
    /// ```
    ///
    /// - Parameter resizingRestrictions: The resizing restrictions to assign to the view's window.
    /// - Returns: A view whose window has the specified resizing restrictions assigned.
    func windowResizingRestrictions(_ resizingRestrictions: UIWindowScene.ResizingRestrictions) -> some View {
        modifier(WindowResizingRestrictionsViewModifier(resizingRestrictions: resizingRestrictions))
    }
    
}

private struct WindowResizingRestrictionsViewModifier: ViewModifier {
    
    let resizingRestrictions: UIWindowScene.ResizingRestrictions
    
    func body(content: Content) -> some View {
        WindowResizingRestrictionsView(resizingRestrictions: resizingRestrictions, content: {
            content
        })
    }
    
}

private struct WindowResizingRestrictionsView<Content>: UIViewControllerRepresentable where Content: View {
    
    let resizingRestrictions: UIWindowScene.ResizingRestrictions
    
    let content: () -> Content
    
    func makeUIViewController(context: Context) -> WindowResizingRestrictionsUIViewController<Content> {
        WindowResizingRestrictionsUIViewController(resizingRestrictions: resizingRestrictions, content: content)
    }
    
    func updateUIViewController(_ uiViewController: WindowResizingRestrictionsUIViewController<Content>, context: Context) {
        // Do nothing.
    }
    
}

private class WindowResizingRestrictionsUIViewController<Content>: UIViewController where Content: View {
    
    private let resizingRestrictions: UIWindowScene.ResizingRestrictions
    
    private let hostingController: UIHostingController<Content>
    
    init(resizingRestrictions: UIWindowScene.ResizingRestrictions, content: @escaping () -> Content) {
        self.resizingRestrictions = resizingRestrictions
        self.hostingController = UIHostingController(rootView: content())
        
        super.init(nibName: nil, bundle: nil)
        
        addChild(hostingController)
        hostingController.view.frame = view.bounds
        view.addSubview(hostingController.view)
        hostingController.didMove(toParent: self)
        
        hostingController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        view = WindowResizingRestrictionsUIView(resizingRestrictions: resizingRestrictions)
    }
    
}

private class WindowResizingRestrictionsUIView: UIView {
    
    private let resizingRestrictions: UIWindowScene.ResizingRestrictions
    
    init(resizingRestrictions: UIWindowScene.ResizingRestrictions) {
        self.resizingRestrictions = resizingRestrictions
        
        super.init(frame: .zero)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func didMoveToWindow() {
        window?.windowScene?.requestGeometryUpdate(.Vision(resizingRestrictions: resizingRestrictions))
    }
    
}