QLThumbnailGenerator doesn't generate the thumbnail - thumbnails

Question

I tried using QLThumbnailGenerator in Simulator/Device for iOS and iPadOS, but it does not work.
I'am able to only obtain a standard empty thumbnail but not the rich icon from my files from documents directory.
Some progress with files in sandbox but nothing useful.
Do you make it work?
Maybe something with the permission is wrong...but what? From my app I am able to list files, and read (open) them.
#IBAction func generateDidSelect(_ sender: Any) {
let docDir = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true).last
print("DOC: \(docDir)")
let absPath = URL(fileURLWithPath: docDir ?? "").appendingPathComponent("flowers.png").absoluteString
//[[NSBundle mainBundle]URLForResource:#"flowers" withExtension:#"png"];
let fileURL = URL(fileURLWithPath: absPath)
fileURL.startAccessingSecurityScopedResource()
let size = CGSize(width: 200, height: 200)
let scale = UIScreen.main.scale
let isFile = fileURL.isFile()
let exists = FileManager.default.fileExists(atPath: fileURL.path)
print("isFILE? \(isFile ? "YES" : "NO") exists? \(exists ? "YES" : "NO") \nFILE: \(fileURL)")
let request = QLThumbnailGenerationRequest(fileAtURL: fileURL, size: size, scale: scale, representationTypes: QLThumbnailGenerationRequestRepresentationTypeAll)
//request.iconMode = YES;
QLThumbnailGenerator.shared().generateRepresentations(for: request, updateHandler: { thumbnail, type, error i
DispatchQueue.main.async(execute: {
print(String(format: "*** TYPE: %ld ****", Int(type)))
let uiimage = thumbnail?.uiImage
let cgImage = thumbnail?.cgImage
if let uiimage = uiimage {
print("uiimage: \(uiimage)")
}
if let cgImage = cgImage {
print("cgImage: \(cgImage)")
}
if uiimage != nil {
self.thumbnailImageView.image = uiimage
}
if error != nil {
if let error = error {
print("ERROR: \(error)")
}
//self.thumbnailImageView.image = [UIImage imageWithContentsOfFile:fileURL.path]; // test read, works
}
})
})
}
Then I tried with an image into the bundle.
Getting the file url with:
Bundle.main.url(forResource: "flowers", withExtension: "png")
and it magically works! ...but no with fileURLWithPath method.
But, accessing the same identical file uploaded via iTunes into the Documents directory of the app i get a read error.
2019-10-01 12:41:27.167091+0200 test_thumb_obj[618:57118] DOC: /var/mobile/Containers/Data/Application/BE4A5950-5D24-4620-A1FE-B837222E8B64/Documents
2019-10-01 12:41:27.196739+0200 test_thumb_obj[618:57118] isFILE? YES exists? YES
FILE: file:///var/mobile/Containers/Data/Application/BE4A5950-5D24-4620-A1FE-B837222E8B64/Documents/flowers.png
2019-10-01 12:41:27.233546+0200 test_thumb_obj[618:57118] *** TYPE: 0 ****
2019-10-01 12:41:27.233788+0200 test_thumb_obj[618:57118] uiimage:
2019-10-01 12:41:27.233858+0200 test_thumb_obj[618:57118] cgImage: (DP)
< (kCGColorSpaceDeviceRGB)>
width = 493, height = 640, bpc = 8, bpp = 32, row bytes = 1984
kCGImageAlphaPremultipliedFirst | kCGImageByteOrder32Little | kCGImagePixelFormatPacked
is mask? No, has masking color? No, has soft mask? No, has matte? No, should interpolate? Yes
2019-10-01 12:41:27.234761+0200 test_thumb_obj[618:57118] *** TYPE: 1 ****
2019-10-01 12:41:27.234836+0200 test_thumb_obj[618:57118] uiimage: (null)
2019-10-01 12:41:27.234865+0200 test_thumb_obj[618:57118] cgImage: (null)
2019-10-01 12:41:27.234943+0200 test_thumb_obj[618:57118] ERROR: Error Domain=QLThumbnailErrorDomain Code=2 "No cached thumbnail"
2019-10-01 12:41:27.262228+0200 test_thumb_obj[618:57118] *** TYPE: 2 ****
2019-10-01 12:41:27.262317+0200 test_thumb_obj[618:57118] uiimage: (null)
2019-10-01 12:41:27.262349+0200 test_thumb_obj[618:57118] cgImage: (null)
2019-10-01 12:41:27.262452+0200 test_thumb_obj[618:57118] ERROR: Error Domain=QLThumbnailErrorDomain Code=0 "Could not generate a thum
bnail" UserInfo={NSUnderlyingError=0x281676940 {Error Domain=NSCocoaErrorDomain Code=256 "The file couldn’t be opened."}}
The only image a get i TYPE = 0, the white empty one.
And, as before, on simulator nothing good....
Error Domain=NSPOSIXErrorDomain Code=22 "couldn't issue sandbox extension com.apple.app-sandbox.read for...
Some test i missed to make it working?

Answer 1

I had the same issue. I resolved it by changing representationTypes from .all to .thumbnail
let request = QLThumbnailGenerator
.Request(fileAt: fileURL, size: size, scale: scale,
representationTypes: .thumbnail)
Or if you like, you can try to create a recursion. After 20-30 calls of generateRepresentations the error "No cached thumbnail" stopped appearing and the image was available.
func thumbnail(for fileURL: URL, size: CGSize, scale: CGFloat) {
QLThumbnailGenerator.shared.generateRepresentations(for: request) { (thumbnail, type, error) in
let uiimage = thumbnail?.uiImage
if uiimage == nil {
thumbnail(fileURL, size, scale)
}
else {
//image is available
}
}
}

Answer 2

Solved on iOS13.2 beta.
On device ok, still read issues on simulator

Answer 3

This worked for me, I create this method:
import QuickLook
...
func generateThumbnailFromQuickLook(url: URL,
type: QLThumbnailGenerator.Request.RepresentationTypes,
completionHandler: #escaping (Bool, UIImage?) -> Void) {
let size = CGSize(width: 300, height: 250)
let scale = UIScreen.main.scale
let request = QLThumbnailGenerator.Request(fileAt: url,
size: size,
scale: scale,
representationTypes: type)
let generator = QLThumbnailGenerator.shared
generator.generateBestRepresentation(for: request) { thumbnail, error in
if let error = error {
print(error)
}
completionHandler(thumbnail != nil, thumbnail?.uiImage)
}
}
Then I check if the representation type thumbnail fail. If it fails, I try to get the representation type all:
let url: URL = <url file>
generateThumbnailFromQuickLook(url: url, type: .thumbnail) { success, image in
if success == false {
generateThumbnailFromQuickLook(url: url, type: .all) { success, image in
// use the thumbnail here
}
} else if let image = image {
// use the thumbnail here
}
}