NSWindow contentView not cover full window size - macOS & SwiftUI

I'm starting a new macOS app with SwiftUI but I have a big problem. The app needs a full size contentView (underneath titleBar) but I can't accomplish. On a new project using Storyboards works fine, but with SwiftUI not.

My code:

Result:

And it should look like this:

Any ideas? Thanks!

I just used the following variant in AppDelegate, the content of ContentView and others can be any

func applicationDidFinishLaunching(_ aNotification: Notification) {
    // Create the SwiftUI view that provides the window contents.
    let contentView = ContentView()
        .edgesIgnoringSafeArea(.top) // to extend entire content under titlebar 

    // Create the window and set the content view. 
    window = NSWindow(
        contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
        styleMask: [.titled, .closable, .miniaturizable, .texturedBackground, .resizable, .fullSizeContentView],
        backing: .buffered, defer: false)
    window.center()
    window.setFrameAutosaveName("Main Window")

    window.titlebarAppearsTransparent = true // as stated
    window.titleVisibility = .hidden         // no title - all in content

    window.contentView = NSHostingView(rootView: contentView)
    window.makeKeyAndOrderFront(nil)
}

Just for more information in the case of SwiftUI App life cycle.

You need to set the window style to HiddenTitleBarWindowStyle :

WindowGroup {
    ContentView()
}.windowStyle(HiddenTitleBarWindowStyle())

The safe area does not extend underneath a transparent title bar. You can use edgesIgnoringSafeArea to tell your content view edges to ignore the safe area. Something that resembles your example:

struct ContentView: View {
  var body: some View {
    HStack(spacing: 0) {
      Text("Hello, World!")
        .frame(maxWidth: 200, maxHeight: .infinity)
        .background(Color.red)
      Text("Hello, World!")
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(Color.black)
    }.edgesIgnoringSafeArea(.all)
  }
}

Update: If you want to use a NavigationView, you have to add edgesIgnoringSafeArea to its contents as well:

struct ContentView: View {
  var body: some View {
    NavigationView {
      Text("Hello, World!")
        .frame(maxWidth: 200, maxHeight: .infinity)
        .background(Color.red)
        .edgesIgnoringSafeArea(.all)

      Text("Hello, World!")
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(Color.black)
        .edgesIgnoringSafeArea(.all)

    }.edgesIgnoringSafeArea(.all)
  }
}

Unfortunately, this will initially show a title bar at the moment, apparently until you force a full window redraw. Once you move the window to a different display or hide and show it again, the title bar disappears. So, my guess is that this will be fixed at some point.

Right now, you can programmatically force a hide & show by adding

DispatchQueue.main.async {
  self.window.orderOut(nil)
  self.window.makeKeyAndOrderFront(nil)
}

after window.makeKeyAndOrderFront(nil) in applicationDidFinishLaunching. It will add a very short animation however. If it bothers you, you may be able to turn that off with NSWindow.animationBehavior or something like that.

Update 2: Apparently, if you remove the initial window.makeKeyAndOrderFront(nil) and replace it with the dispatch queue logic above it won't animate. So in the end you'll have

func applicationDidFinishLaunching(_ aNotification: Notification) {
  let contentView = ContentView()

  window = NSWindow(
      contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
      styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView, .texturedBackground],
      backing: .buffered, defer: false)
  window.titlebarAppearsTransparent = true
  window.center()
  window.setFrameAutosaveName("Main Window")
  window.contentView = NSHostingView(rootView: contentView)
  // window.makeKeyAndOrderFront(self) <- don't call it here
  DispatchQueue.main.async {
    self.window.orderOut(nil)
    self.window.makeKeyAndOrderFront(nil)
  }
}