A SwiftUI MenuBarExtra window with custom corners

CustomMenuBarExtraCornerMask.swift

//
//  MenuBarTestApp.swift
//  MenuBarTest
//
//  Created by Stephan Casas on 7/7/23.
//

import SwiftUI

@main
struct MenuBarTestApp: App {
    var body: some Scene {
        MenuBarExtra(content: {
            ContentView()
                .background(MenuBarExtraWindowHelperView())
        }, label: { Image(systemName: "camera.viewfinder") })
        .menuBarExtraStyle(.window)
    }
}

// MARK: - Content

struct ContentView: View {
    var body: some View {
        VStack(content: {
            
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
            
        })
        .frame(width: 500, height: 500)
    }
}


// MARK: - Lossless Method Exchanger

extension NSObject {
    
    /// Swap the given named instance method of the given named class with the given
    /// named instance method of this class.
    /// - Parameters:
    ///   - method: The name of the instance method whose implementation will be exchanged.
    ///   - className: The name of the class whose instance method implementation will be exchanged.
    ///   - newMethod: The name of the instance method on this class which will replace the first given method.
    static func exchange(method: String, in className: String, for newMethod: String) {
        guard let classRef = objc_getClass(className) as? AnyClass,
              let original = class_getInstanceMethod(classRef, Selector((method))),
              let replacement = class_getInstanceMethod(self, Selector((newMethod)))
        else {
            fatalError("Could not exchange method \(method) on class \(className).");
        }
        
        method_exchangeImplementations(original, replacement);
    }
    
}

// MARK: - Custom Window Corner Mask Implementation

/// Exchange Flag
///
var __SwiftUIMenuBarExtraPanel___cornerMask__didExchange = false;

/// Custom Corner Radius
///
fileprivate let kWindowCornerRadius: CGFloat = 40;

extension NSObject {
    
    @objc func __SwiftUIMenuBarExtraPanel___cornerMask() -> NSImage? {
        let width = kWindowCornerRadius * 2;
        let height = kWindowCornerRadius * 2;
        
        let image = NSImage(size: CGSizeMake(width, height));
        
        image.lockFocus();
        
        /// Draw a rounded-rectangle corner mask.
        ///
        NSColor.black.setFill();
        NSBezierPath(
            roundedRect: CGRectMake(0, 0, width, height),
            xRadius: kWindowCornerRadius,
            yRadius: kWindowCornerRadius).fill();
        
        image.unlockFocus();

        image.capInsets = .init(
            top: kWindowCornerRadius,
            left: kWindowCornerRadius,
            bottom: kWindowCornerRadius,
            right: kWindowCornerRadius);
        
        return image;
    }
    
}

// MARK: - Context Window Accessor

struct MenuBarExtraWindowHelperView: NSViewRepresentable {
    
    class WindowHelper: NSView {
        
        override func viewWillDraw() {
            if __SwiftUIMenuBarExtraPanel___cornerMask__didExchange { return }
            
            guard
                let window: AnyObject = self.window,
                let windowClass = window.className
            else { return }
            

            NSObject.exchange(
                method: "_cornerMask",
                in: windowClass,
                for: "__SwiftUIMenuBarExtraPanel___cornerMask");
            
            let _ = window.perform(Selector(("_cornerMaskChanged")));
            
            __SwiftUIMenuBarExtraPanel___cornerMask__didExchange = true;
           
        }
        
    }
    
    func updateNSView(_ nsView: WindowHelper, context: Context) { }
    
    func makeNSView(context: Context) -> WindowHelper { WindowHelper() }
}

A curious question, what license would this code be under?

–Mike 😃

@mike-n-1974 MIT. Have fun!