NEW! Pre-order my latest book, Testing Swift! >>

How to preview files using Quick Look and QLPreviewController

Paul Hudson       @twostraws

Apple’s Quick Look framework lets you embed previewing for a huge range of file types, including iWork documents, Microsoft Office documents, PDFs, images, and more, all without writing much code.

First, import the QuickLook framework, then make your view controller conform to the QLPreviewControllerDataSource protocol. This protocol lets you provide items to Quick Look, which should be URLs pointing to whatever documents you’re trying to preview.

Now go ahead and create and present an instance of QLPreviewController, setting your view controller to be its data source:

let previewController = QLPreviewController()
previewController.dataSource = self
present(previewController, animated: true)

There are two methods you need to implement: how many items your Quick Look controller should show, and the URL for each item. The first of those is just a matter of returning an integer from numberOfPreviewItems():

func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
    return 3
}

Now for the important part: Quick Look will call a previewItemAt method for each item you want to preview, and you need to pass back a QLPreviewItem pointing at it.

For this example I added three PDF files – 0.pdf, 1.pdf, and 2.pdf – to my project, so I’m going to pass back URLs to each of them. URL conforms to QLPreviewItem already, so we can just do an as typecast to make this work:

func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -> QLPreviewItem {
    guard let url = Bundle.main.url(forResource: String(index), withExtension: "pdf") else {
        fatalError("Could not load \(index).pdf")
    }

    return url as QLPreviewItem
}

When that runs you’ll be able to swipe horizontally through Quick Look items, or swipe up and down through pages in your PDFs.

Available from iOS 4.0

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Swift on the server is here

Get ahead of the game and learn server-side Swift with my latest book – build real-world projects while you learn!

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Average rating: 5.0/5

Click here to visit the Hacking with Swift store >>