Swift playground：获取ViewController来调用presentViewController

Question

I would like to play with UIAlertController in Playground. Is it possible to get the ViewController from XCPlaygroundPage - to be able to call presentViewController?

Answer 1

You can set the liveView to your Window after presenting, to avoid the warning.

import UIKit
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true
let window = UIWindow()
let viewController = UIViewController()
window.rootViewController = viewController
window.makeKeyAndVisible()

let alert = UIAlertController(title: "title here", message: "message here", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "action here", style: .default, handler: nil))
viewController.present(alert, animated: true, completion: nil)
PlaygroundPage.current.liveView = window

Result:

Answer 2

Yes, you can certainly get a view controller, but because there's no "attached" view controller you'll end up seeing a warning that looks like this:

Presenting view controllers on detached view controllers is discouraged

And in my case, the alert controller flash on screen super briefly and then disappeared. Perhaps you could improve upon this somewhat?

Anyways, here is how I created the view controllers in the playground:

import UIKit
import XCPlayground

class RootViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.frame = CGRect(x: 0, y: 0, width: 350, height: 420)
        self.view.backgroundColor = UIColor.redColor()
    }
}

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    var tableView: UITableView!
    let items = ["Hello 1", "Hello 2", "Hello 3"]
    var alertController : UIAlertController? {
        didSet {
            if alertController == nil {
                print("alertController set to nil")
            } else {
                print("alertController set to \(alertController)")
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.frame = CGRect(x: 0, y: 0, width: 320, height: 480)
        self.tableView = UITableView(frame:self.view.frame)
        self.tableView!.dataSource = self
        self.tableView!.registerClass(UITableViewCell.self, forCellReuseIdentifier: "cell")
        self.view.addSubview(self.tableView)

    }
    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int{
        return self.items.count;
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{
        let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as UITableViewCell
        cell.textLabel?.text = "\(self.items[indexPath.row])"
        return cell
    }

    override func viewDidAppear(animated: Bool) {
        alertController = UIAlertController.init(title: "My Title", message: "Testing in Playground", preferredStyle: .Alert)

        let okAction = UIAlertAction(title: "Ok", style: .Default) { (_) -> Void in
            // Some action here
            print("hit okay button")
        }

        alertController!.addAction(okAction)

        ctrl.presentViewController(alertController!, animated: false, completion: {
            print("done presenting")
        })
    }
}

var ctrl = ViewController()
var rootVC = RootViewController()
rootVC.addChildViewController(ctrl)
rootVC.view.addSubview(ctrl.view)
XCPlaygroundPage.currentPage.liveView = rootVC.view

And what I'm doing here is I create a "root view controller", add a child view controller with a table (in an attempt to get some view controller "attached" to something else) and then I tried to present an alert controller on that.