SwiftUI View to NSImage in AppKit - swift

Question

SwiftUI 2.0 | Swift 5.4 | Xcode 12.4 | macOS Big Sur 11.4
In iOS there is a way to render SwiftUI views to a UIImage that doesn't work in AppKit, only UIKit:
extension View {
func snapshot() -> UIImage {
let controller = UIHostingController(rootView: self)
let view = controller.view
let targetSize = controller.view.intrinsicContentSize
view?.bounds = CGRect(origin: .zero, size: targetSize)
view?.backgroundColor = .clear
let renderer = UIGraphicsImageRenderer(size: targetSize)
return renderer.image { _ in
view?.drawHierarchy(in: controller.view.bounds, afterScreenUpdates: true)
}
}
}
Is there any workaround to get that working on AppKit? The method UIGraphicsImageRenderer(size:) doesn't work on AppKit and there is no equivalent.

Answer 1

If I'm understanding your question correctly, you should be able to use an NSBitmapImageRef to do the trick!
Here's a simple example of generating an NSImage from SwiftUI view (Note: your host view must be visible!):
let view = MyView() // some SwiftUI view
let host = NSHostingView(rootView: view)
// Note: the host must be visible on screen, which I am guessing you already have it that way. If not, do that here.
let bitmapRep = host.bitmapImageRepForCachingDisplay(in: host.bounds)
host.cacheDisplay(in: host.bounds, to: bitmapRep!)
let image = NSImage(size: host.frame.size)
image.addRepresentation(bitmapRep!)
Here's an extension to NSHostingView that should safely make snapshots:
extension NSHostingView {
func snapshot() -> NSImage? {
// Make sure the view is visible:
guard self.window != nil else { return nil }
// Get bitmap data:
let bitmapRep = self.bitmapImageRepForCachingDisplay(in:
self.bounds)
self.cacheDisplay(in: self.bounds, to: bitmapRep!)
// Create NSImage from NSBitmapImageRep:
let image = NSImage(size: self.frame.size)
image.addRepresentation(bitmapRep!)
return image
}
}
I hope this helps. Let me know if you have any questions!