Have a fullSizeContentView NSWindow taking the size of a SwiftUI view

Question

I want an NSWindow with fullSizeContentView to take the exact size of a SwiftUI view that has an intrinsic content size. I saw similar posts like this one but they were different in that it was fine to provide a fixed frame at a top level. I don’t want to do that, I want the window size to be exactly the size of the view. How can I do that?

This is a Playground snippet that runs in Xcode 14.1.

import AppKit
import SwiftUI

class MyWindow: NSWindow {
    override func setFrame(_ frameRect: NSRect, display flag: Bool) {
        print("\(Date().timeIntervalSince1970) setFrame called \(frameRect)")
        super.setFrame(frameRect, display: flag)
    }
}

let window = MyWindow()

window.styleMask = [
    .titled,
    .closable,
    .resizable,
    .fullSizeContentView
]

window.toolbar = nil

window.titlebarAppearsTransparent = true
window.titleVisibility = .hidden
window.isMovable = true
window.isMovableByWindowBackground = true
window.standardWindowButton(.closeButton)?.isHidden = false
window.standardWindowButton(.miniaturizeButton)?.isHidden = true
window.standardWindowButton(.zoomButton)?.isHidden = true

print("\(Date().timeIntervalSince1970) Before content \(window.frame)")
window.contentView = NSHostingView(rootView: ContentView())
print("\(Date().timeIntervalSince1970) After setting content \(window.frame)")

window.makeKeyAndOrderFront(nil)

print("\(Date().timeIntervalSince1970) After makeKeyAndOrderFront \(window.frame)")

DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
    print("\(Date().timeIntervalSince1970) After 1 second \(window.frame)")
}

struct ContentView: View {
    var body: some View {
        Text("Hello")
            .font(.system(size: 200))
            .background(.blue)
            .fixedSize()
            .ignoresSafeArea()
    }
}

The problem is that it leaves some space at the end. Why is this code behaving like that?

It prints this:

1674086812.362426 setFrame called (100.0, 100.0, 100.0, 100.0)
1674086812.363435 Before content (100.0, 100.0, 100.0, 100.0)
1674086812.373186 setFrame called (100.0, -63.0, 431.0, 263.0)
1674086812.3741732 After setting content (100.0, -63.0, 431.0, 263.0)
1674086812.374618 setFrame called (100.0, 85.0, 431.0, 263.0)
1674086812.375651 After makeKeyAndOrderFront (100.0, 85.0, 431.0, 263.0)
1674086812.4359 setFrame called (100.0, 57.0, 431.0, 291.0)
1674086813.41998 After 1 second (198.0, 99.0, 431.0, 291.0)

Why is SwiftUI setting the frame with a different size after showing it?

To make it easier to answer your question, can you please create a [mcve]. The code you have supplied doesn't compile — Ashley Mills, Jan 19 '23 at 09:25
It works for me. It's a Playgrounds snippet. Copy and paste the code in Playgrounds, run it and it should work. I am using Xcode 14.1. — narduk, Jan 19 '23 at 11:43
Ah, thanks, of course - I was pasting it into an Xcode project. — Ashley Mills, Jan 19 '23 at 11:45

score 2 · Accepted Answer · answered Jan 30 '23 at 20:31

Ok, after spending a lot of time struggling with this, I think I found a workaround. The idea is to avoid completely ignoreSafeArea which seems buggy. In order to do that, I suppressed safe area behavior on the AppKit side by extending NSHostingView and overriding safe area related behavior. This is the code.

import AppKit
import SwiftUI

class MyWindow: NSWindow {
    override func setFrame(_ frameRect: NSRect, display flag: Bool) {
        print("\(Date().timeIntervalSince1970) setFrame called \(frameRect)")
        super.setFrame(frameRect, display: flag)
    }
}

let window = MyWindow()

window.styleMask = [
    .titled,
    .closable,
    .resizable,
    .fullSizeContentView
]

window.titlebarAppearsTransparent = true
window.titleVisibility = .hidden
window.isMovable = true
window.isMovableByWindowBackground = true
window.standardWindowButton(.closeButton)?.isHidden = false
window.standardWindowButton(.miniaturizeButton)?.isHidden = true
window.standardWindowButton(.zoomButton)?.isHidden = true

class NSHostingViewSuppressingSafeArea<T : View>: NSHostingView<T> {
    required init(rootView: T) {
        super.init(rootView: rootView)

        addLayoutGuide(layoutGuide)
        NSLayoutConstraint.activate([
            leadingAnchor.constraint(equalTo: layoutGuide.leadingAnchor),
            topAnchor.constraint(equalTo: layoutGuide.topAnchor),
            trailingAnchor.constraint(equalTo: layoutGuide.trailingAnchor),
            bottomAnchor.constraint(equalTo: layoutGuide.bottomAnchor)
        ])
    }

    private lazy var layoutGuide = NSLayoutGuide()

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override var safeAreaRect: NSRect {
        print ("super.safeAreaRect \(super.safeAreaRect)")
        return frame
    }

    override var safeAreaInsets: NSEdgeInsets {
        print ("super.safeAreaInsets \(super.safeAreaInsets)")
        return NSEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
    }

    override var safeAreaLayoutGuide: NSLayoutGuide {
        print ("super.safeAreaLayoutGuide \(super.safeAreaLayoutGuide)")
        return layoutGuide
    }

    override var additionalSafeAreaInsets: NSEdgeInsets {
        get {
            print ("super.additionalSafeAreaInsets \(super.additionalSafeAreaInsets)")
            return NSEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
        }

        set {
            print("additionalSafeAreaInsets.set \(newValue)")
        }
    }
}

print("\(Date().timeIntervalSince1970) Before content \(window.frame)")
window.contentView = NSHostingViewSuppressingSafeArea(rootView: ContentView())
print("\(Date().timeIntervalSince1970) After setting content \(window.frame)")

window.makeKeyAndOrderFront(nil)

print("\(Date().timeIntervalSince1970) After makeKeyAndOrderFront \(window.frame)")

DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
    print("\(Date().timeIntervalSince1970) After 1 second \(window.frame)")
}

struct ContentView: View {
    var body: some View {
        Text("Hello")
            .font(.system(size: 200))
            .fixedSize()
            .background(.blue)
    }
}

The result is:

And it prints this:

1675110465.322774 setFrame called (100.0, 100.0, 100.0, 100.0)
1675110465.332483 Before content (100.0, 100.0, 100.0, 100.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
1675110465.3494139 setFrame called (100.0, -35.0, 431.0, 235.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
super.safeAreaInsets NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
1675110465.3513222 After setting content (100.0, -35.0, 431.0, 235.0)
1675110465.352477 setFrame called (100.0, 85.0, 431.0, 235.0)
1675110465.3534908 After makeKeyAndOrderFront (100.0, 85.0, 431.0, 235.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
super.additionalSafeAreaInsets NSEdgeInsets(top: 0.0, left: 0.0, bottom: 0.0, right: 0.0)
additionalSafeAreaInsets.set NSEdgeInsets(top: 28.0, left: 0.0, bottom: 0.0, right: 0.0)
1675110466.401649 After 1 second (636.0, 490.0, 431.0, 235.0)

Ashley Mills · Answer 2 · 2023-01-19T17:45:05.503

The problem is your ordering of modifiers. You've put .background before .ignoresSafeArea(), so the background takes the safe area into account, If you re-order as follows, it works as required:

struct ContentView: View {
    var body: some View {
        Text("Hello")
            .font(.system(size: 200))
            .fixedSize()
            .ignoresSafeArea()
            .background(.blue)
    }
}

Second attempt

Adding some borders to the views after modifiers, it seems that the text is overlapping the title bar, and is inset that amount from the bottom.

struct ContentView: View {
    
    var body: some View {
        Text("Hello")
            .font(.system(size: 200))
            .fixedSize()
            .border(.pink, width: 2)
            .ignoresSafeArea()
            .border(.yellow, width: 1)
            .background(.blue.opacity(0.5))
    }
}

Applying a small offset to the View after .ignoresSafeArea()

.ignoresSafeArea()
.offset(y: 0.1)
.background(.blue)

gives:

If you do the same after the .background modifier, the title bar is shown:

.ignoresSafeArea()
.offset(y: 0.1)
.background(.blue)

I don't know why an offset seems to fix the problem.

Thanks for the suggestion! The problem I see with this solution is that it is actually taking more space than the actual content. In this example, the content wants to have a height of 235. To measure that, I put the content in a very big frame and measured the background. But here, the background ends up being larger, specifically, 291. As I stated in my question, I want the window to take the size of the content, not more, not less. — narduk, Jan 19 '23 at 13:33
I'v done some more research into the problem, with a potential workaround. — Ashley Mills, Jan 19 '23 at 17:45
Thanks for doing the research! Unfortunately, the workaround doesn't have the right height yet. It moved the text down a bit but the size of the window is still larger than the ideal size. — narduk, Jan 19 '23 at 21:28

Have a fullSizeContentView NSWindow taking the size of a SwiftUI view

2 Answers2