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Swift macOS generate image previews of files on disk
func generatePreview() {
guard let fileURL = upload?.fileURL else { return }
do {
let values = try fileURL.resourceValues(forKeys: [URLResourceKey.typeIdentifierKey])
if let type = values.typeIdentifier,
UTTypeConformsTo(type as CFString, kUTTypeImage) {
if let imageData = FileManager.default.contents(atPath: fileURL.path) {
self.imagePreview.image = NSImage(data: imageData)
catch {
Logger.error("Failed to lookup resource values")
import AppKit
import QuickLook
extension NSImage {
static func previewForFile(path fileURL: URL, ofSize size: CGSize, asIcon: Bool) -> NSImage? {
let dict = [
kQLThumbnailOptionIconModeKey: NSNumber(booleanLiteral: asIcon)
] as CFDictionary
let ref = QLThumbnailImageCreate(kCFAllocatorDefault, fileURL as CFURL, size, dict)
if let cgImage = ref?.takeUnretainedValue() {
// Take advantage of NSBitmapImageRep's -initWithCGImage: initializer, new in Leopard,
// which is a lot more efficient than copying pixel data into a brand new NSImage.
// Thanks to Troy Stephens @ Apple for pointing this new method out to me.
let bitmapImageRep = NSBitmapImageRep.init(cgImage: cgImage)
let newImage = NSImage.init(size: bitmapImageRep.size)
return newImage
} else {
// If we couldn't get a Quick Look preview, fall back on the file's Finder icon.
let icon = NSWorkspace.shared.icon(forFile: fileURL.path)
icon.size = size
return icon

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@phawk phawk commented Feb 15, 2018

NSImage+QuickLook original taken from and ported to swift4


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@fukemy fukemy commented Mar 27, 2021

hi, any solution for swift?

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