Swift playground:获取ViewController来调用presentViewController

Question

我想在Playground玩UIAlertController.是否有可能从XCPlaygroundPage获取ViewController - 能够调用presentViewController？

Answer 1

您可以设置实时查看到你的窗口后提出,以避免该警告.

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

结果:

Answer 2

是的，您当然可以获得一个视图控制器，但是因为没有“附加”视图控制器，您最终会看到如下所示的警告：

Presenting view controllers on detached view controllers is discouraged

就我而言，警报控制器在屏幕上短暂闪烁，然后消失。也许你可以对此进行一些改进？

无论如何，这是我在操场上创建视图控制器的方法：

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

我在这里所做的是创建一个“根视图控制器”，添加一个带有表的子视图控制器（试图将一些视图控制器“附加”到其他东西上），然后我尝试呈现一个警报控制器关于这一点。