How to find the largest size of a view that does not make window larger than screen size?

Question

I'm working on a MacOS application that needs to display large images. if I naively set the ImageView to be the full size image, the application's window can be forced to become larger than the screen size. What I'd like to be able to do is work out how large I can make the image while keeping the entire window (which also contains other UI elements) on screen.

I know I can query the amount of available screen space using NSScreen:visibleFrame() but that does not seem to be much help since unless I make a whole load of assumptions about how much space the rest of the UI will take up which then defeats the point of having constraint based UI layout.

The other approach could be to find a way to constrain the window size and then let Cocoa work out the sizes of the views. However, it looks like the UI editors in Xcode only allows static sizes to be specified which is not much help.

It looks like this is possible in SwiftUI (https://www.hackingwithswift.com/quick-start/swiftui/how-to-adjust-the-way-an-image-is-fitted-to-its-space)

Image("example-image")
   .resizable()
   .aspectRatio(contentMode: .fit)

However, the application I'm working on needs to run on older versions of MacOS than supported by SwiftUI so I need to know how to do this in swift but using plain Cocoa.

Ken Thomases Ken Thomases · Accepted Answer · 2020-04-06T21:28:13

The first thing I would try is to modify the priority of the constraints that make the image view large enough to accommodate the image. That would be its content compression resistance priority. I think if you set it to .dragThatCanResizeWindow then you might get the behavior you want for free. That's because the system already constrains a window to the screen size when you drag its edges. So, presumably, that implicit constraint has a higher priority than .dragThatCanResizeWindow.

If that doesn't do it, you can programmatically set a window's maximum frame size by setting its maxSize property. You'll want to set that each time the screen configuration changes or the window moves to a different screen. For the former, you can observe NSApplication.didChangeScreenParametersNotification. For the latter, your window delegate can implement windowDidChangeScreen(_:) or you can observe NSWindow.didChangeScreenNotification.

How to find the largest size of a view that does not make window larger than screen size?

1 Answers