Playground in Xcode 8

During session 213 of WWDC 2016, some changes to Playground in Xcode 8 were mentioned. The talk shows more tips and tricks to make use of the powerful Xcode features such as Assets Catalogs to avoid writing more code than what is necessary. I highly reccomend you to watch it!

To manage the execution of a Playground, the PlaygroundSupport framework can now be used. By ⌘ + clicking the framework name, this is what you can find:

• A UIViewController and UIView extension that implement the PlaygroundLiveViewable protocol.
• The PlaygroundLiveViewRepresentation enum which describes if the current live view shows a UIView or a UIViewController.
• The PlaygroundLiveViewable protocol itself that has a variable to hold the current live view representation.
• The PlaygroundPage class that allows you to modify the playground execution.

A Playground is compiled like a script, line after line. This is great until you want to test a network request that is performed asynchronously. You will never see the callback result because the Playground is simply stopped before the response can arrive. To fix this problem you have to tell Xcode that your page needsIndefiniteExecution. Let’s take a look at a common URLSession usage.

    import UIKit
    import PlaygroundSupport
    
    PlaygroundPage.current.needsIndefiniteExecution = true
    
    let url = URL(string: "https://emergency-phone-numbers.herokuapp.com")!
    let session = URLSession.shared()
    let q = session.dataTask(with: url) { data, response, error in
        do {
            if let d = data, let dictionary = try JSONSerialization.jsonObject(with: d, options: []) as? [String: AnyObject] {
                print(dictionary)
            }
        } catch {
            print("Error \(error)")
        }
    }
    q.resume()

We first import the new PlaygroundSupport framework at the top. We then set the PlaygroundPage.current.needsIndefiniteExecution property to true so that the playground will continue the execution of the Swift file even after reaching the last line. In this way, we are able to debug and see the response of our request.

You can also tell your Playground to stop waiting for something to happen. You could for example add this line in your completion handler to stop the execution of the page.

    PlaygroundPage.current.finishExecution()

Another cool feature shown in the session which was added in Xcode 7.3, is the ability to interact with the live view. You can for example create a UIViewController and assign it to the Playground liveView as follows:

    PlaygroundPage.current.liveView = viewController.view

This is useful to test a component before actually implement it into your project. To read more about this specific feature, watch the WWDC session 213 video or read this blog post on the Swift official blog.

Thanks for reading 🤓