How to disabled fullscreen button on MacCatalyst

Question

Currently, I have this to stop resizing window:

#if targetEnvironment(macCatalyst)
windowScene.sizeRestrictions?.minimumSize = CGSize(width: 480, height: 900)
windowScene.sizeRestrictions?.maximumSize = CGSize(width: 480, height: 900)
#endif

let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()

but the fullscreen button makes it full screen anyway.

Answer 1

It's a bit complicated but possible. Here is an approach (I dropped all target macros to simplify post).

Result:

Code:

// on next event after UIWindow has made key it is possible to find NSWindow in runtime

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

        ...
        window.makeKeyAndVisible()

        DispatchQueue.main.async { // < wait for NSWindow available
            SilentBridge.disableCloseButton(for: self.nsWindow(from: window))
        }
    }

// added helper function to SceneDelegate to find NSWindow

    func nsWindow(from window: UIWindow) -> NSObject? {
        guard let nsWindows = NSClassFromString("NSApplication")?.value(forKeyPath: "sharedApplication.windows") as? [NSObject] else { return nil }
        for nsWindow in nsWindows {
            let uiWindows = nsWindow.value(forKeyPath: "uiWindows") as? [UIWindow] ?? []
            if uiWindows.contains(window) {
                return nsWindow
            }
        }
        return nil
    }

Objective-C part is preferred (it's just simpler to work with non-declared selectors). Add new Objective-C class via Xcode template and confirm creating bridge. Afterwards it is needed to add below class header file in generated *-Bridging-Header.h and all should work.

// SilentBridge.h

@import Foundation;

@interface SilentBridge : NSObject
+ (void)disableCloseButtonFor:(NSObject  * _Nullable)window;
@end

// SilentBridge.m

#import "SilentBridge.h"
@import Foundation;

// Forward declarations to allow direct calls in below method
@interface NSObject(SilentBridge) 
- (id)standardWindowButton:(NSInteger)value;
- (void)setEnabled:(BOOL)flag;
@end

@implementation SilentBridge

+ (void)disableCloseButtonFor:(NSObject *)window {
    if ([window respondsToSelector:@selector(standardWindowButton:)]) {
        id closeButton = [window standardWindowButton:2];
        if ([closeButton respondsToSelector:@selector(setEnabled:)]) {
            [closeButton setEnabled:NO];
        }
    }
}
@end