尝试为 cloudkit 共享创建缩略图，但是

Question

iOS 11.x 斯威夫特 4.2

创建 cloudKit 共享并为其设置权限。一切看起来都不错并且有效，但是对于缩略图，我收到以下错误消息，这超出了我的范围。它在说什么？

2018-10-10 11:04:14.422093+0200 n2k Memo[12256:5302161] [DocumentManager] 无法关联所选 URL file:///private/var/mobile/Library/Mobile%20Documents/com~apple~ 的缩略图CloudDocs/Desktop/August2018/App/Icons/noun_Puzzle_787736.png 以及收件箱副本文件:///private/var/mobile/Containers/Data/Application/D13D04E1-8700-4B3E-AD0B-710D037B5253/tmp/ch.cqd。 blah-Inbox/noun_Puzzle_787736.png：错误域=QLThumbnail代码=2“（空）”UserInfo={NSUnderlyingError=0x1c444b070 {错误域=GSLibraryErrorDomain代码=3“找不到生成”UserInfo={NSDescription=找不到生成}}}

我的代码看起来像这样......

let share = CKShare(rootRecord: customRecord)
share[CKShare.SystemFieldKey.title] = "Marley" as CKRecordValue
share[CKShare.SystemFieldKey.shareType] = "ch.cqd.blah" as CKRecordValue

let imageData = image2Save.pngData()!
let options = [
        kCGImageSourceCreateThumbnailWithTransform: true,
        kCGImageSourceCreateThumbnailFromImageAlways: true,
        kCGImageSourceThumbnailMaxPixelSize: 300] as CFDictionary
let source = CGImageSourceCreateWithData(imageData as CFData, nil)!
let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options)!
let thumbnail = UIImage(cgImage: imageReference).pngData()
share[CKShare.SystemFieldKey.thumbnailImageData] = thumbnail! as CKRecordValue

image2Save 是我随后显示的有效 UIImage。添加了在屏幕上显示缩略图的代码。缩略图看起来不错。