子视图在XCode Playground中不起作用

Question

I was trying to add a subview of type UIView to my primary view. This does not work accordingly however. I would think that this should change the screen to red and have a text. Do any of you have an idea what the problem can be?

import UIKit
import Foundation
import PlaygroundSupport

class SecondView : UIView{

  func loadView() {
     let secondViewController = SecondView()
     let label = UILabel()
     label.frame = CGRect(x: 0, y: 335, width: 400, height: 53)

     label.textAlignment = .center
     label.font = UIFont(name: "helveticaneue-ultraLight", size: 40)
     label.text = "Hejsan"
     label.textColor = .white

     secondViewController.addSubview(label)
      print("Test")
}

 }

  class MyViewController : UIViewController {

   //Outlets
   let profileButton = UIButton()

     override func loadView() {
      let view = UIView()

      view.backgroundColor = .green
      print(view.frame)

     let sView = SecondView()
     sView.backgroundColor = .red
     sView.frame = view.frame

     view.addSubview(sView)

     print(sView.frame)

     self.view = view

   }
 }
// Present the view controller in the Live View window

PlaygroundPage.current.liveView = MyViewController()

Answer 1

You are doing so many things wrong :(

This will run in a playground page, and should be close to what you're going for. Check the comments to understand what's going on:

import UIKit
import Foundation
import PlaygroundSupport

class SecondView : UIView{

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }

    func commonInit() {

        // create a label
        let label = UILabel()
        // we're going to use auto-layout
        label.translatesAutoresizingMaskIntoConstraints = false

        // add the label to self
        self.addSubview(label)

        // pin the label to leading, trailing and bottom -- all to Zero
        label.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 0.0).isActive = true
        label.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: 0.0).isActive = true
        label.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: 0.0).isActive = true

        label.textAlignment = .center
        label.font = UIFont(name: "helveticaneue-ultraLight", size: 40)
        label.text = "Hejsan"
        label.textColor = .white

    }

}

class MyViewController : UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // we don't need to create a new view
        //let view = UIView()

        view.backgroundColor = .green

        // create the "SecondView"
        let sView = SecondView()
        // we're going to use auto-layout
        sView.translatesAutoresizingMaskIntoConstraints = false

        // add the new view
        view.addSubview(sView)

        // pin the new view to top, leading and trailing -- all to Zero so it fills this view
        sView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
        sView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0.0).isActive = true
        sView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
        sView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true

        sView.backgroundColor = .red

    }

}

// Present the view controller in the Live View window

let vc = MyViewController()
vc.preferredContentSize = CGSize(width: 375, height: 667)
PlaygroundPage.current.liveView = vc

Result:

Answer 2

loadView is a UIViewController lifecycle callback method (see docs ).

Your SecondView is a subclass of UIView that does not define loadView . Therefore the loadView you implemented in SecondView does not get called by the environment. You will have to call it explicitly:

let sView = SecondView()
sView.backgroundColor = .red
sView.frame = view.frame

sView.loadView()

view.addSubview(sView)

Moreover, I would recommend to rename it (so that it would confuse with the UIViewController 's loadView .

UPDATE

There are several other errors there.

1 : In your loadView of the second view you are creating a new SecondView and add the label to it. You need to add it to self .

2 : In loadView of the viewController, you are creating a new view with UIView() which defaults to UIView(frame: CGRect.zero) and then you set sView.frame = view.frame which will make the frame of the second view CGRect.zero too. view will be stretched by the UIViewController environment, but the frame of the sView will not be updated. There are several options how to do it, but simplest is to initialize the view with a proper frame from the beginning. Working playground solution:

import UIKit
import Foundation
import PlaygroundSupport

class SecondView : UIView{

    func loadView() {
        let label = UILabel()
        label.frame = CGRect(x: 0, y: 335, width: 400, height: 53)

        label.textAlignment = .center
        label.font = UIFont(name: "helveticaneue-ultraLight", size: 40)
        label.text = "Hejsan"
        label.textColor = .white

        self.addSubview(label)
        print("Test")
    }

}

class MyViewController : UIViewController {

    //Outlets
    let profileButton = UIButton()

    override func loadView() {
        let view = UIView(frame: UIScreen.main.bounds)

        view.backgroundColor = .green
        print(view.frame)

        let sView = SecondView()
        sView.backgroundColor = .red
        sView.frame = view.frame
        sView.loadView()

        view.addSubview(sView)

        print(sView.frame)

        self.view = view

    }
}
// Present the view controller in the Live View window

PlaygroundPage.current.liveView = MyViewController()

Answer 3

Right way to declare a subview

class SecondView: UIView {

    override init(frame: CGRect) {
        super.init(frame: frame)
        sharedLayout()

    }

    required init(coder aDecoder: NSCoder) {
        super.init(coder : aDecoder)
        sharedLayout()
    }

    func sharedLayout()
    {
         let label = UILabel()
         label.frame = CGRect(x: 0, y: 335, width: 400, height: 53)
         label.textAlignment = .center
         label.font = UIFont(name: "helveticaneue-ultraLight", size: 40)
         label.text = "Hejsan"
         label.textColor = .white
         self.addSubview(label)
         print("Test")
    }

}