Quicklook始终显示“无文件可预览”错误（URL有效）

Question

I'm trying to use QuickLookController subclass as a child controller, setting its view as a subview in the parent. However, it always displays "no file to preview" message in the opening window. URL in the data source is valid, but the controller is never trying to get it! func previewItemAt index is never invoked!
func "numberOfPreviewItems" invokes always.
Please, help!

Answer 1

I get it. driven by example in article https://williamboles.me/hosting-viewcontrollers-in-cells/ I loaded my controller from bundle:

static func createFromStoryBoard() -> PreviewControler {
    let storyboard = UIStoryboard(name: "PreviewControler", bundle: Bundle(for: PreviewControler.self))
    guard let viewController = storyboard.instantiateViewController(withIdentifier: "PreviewControler") as? PreviewControler else {
        fatalError("PreviewControler should be present in storyboard")
    }
    return viewController
}

But QuickLook controller must be created with it's constructor, so change to

let viewController = PreviewController()

solved the problem. Now all is fine.