在iOS Playground应用程序的viewcontroller内部将视图居中

Question

I'm currently building a swift playground book. Is it possible to center a view inside a view controller while running on an iPad ?

Here's my loadView function of my view controller:

override public func loadView() {
    let view = UIView()
    view.backgroundColor = .white
    view.frame = CGRect(x: 0, y: 0, width: 375, height: 667)
    self.view = view

    let frame = CGRect(x: 0, y: 0, width: 375, height: 375)
    let newView = UIView(frame: frame)
    view.addSubview(newView)
}

How can I center the newView in the view of the view controller?

Thanks !

Answer 1

You can try to do it using Autolayout:

let frame = CGRect(x: 0, y: 0, width: 375, height: 375)
let newView = UIView(frame: frame)
view.addSubview(newView)
newView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
    newView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
    newView.leftAnchor.constraint(equalTo: view.leftAnchor),
    newView.rightAnchor.constraint(equalTo: view.rightAnchor),
    newView.widthAnchor.constraint(equalTo: newView.heightAnchor),
])
newView.backgroundColor = UIColor.red

UPDATE

Playground code:

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .red
        view.frame = CGRect(x: 0, y: 0, width: 375, height: 667)
        self.view = view

        let frame = CGRect(x: 0, y: 0, width: 375, height: 375)
        let newView = UIView(frame: frame)
        newView.backgroundColor = .blue
        view.addSubview(newView)

        newView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            newView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            newView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            // need to define its size too
            newView.heightAnchor.constraint(equalToConstant: 375),
            newView.widthAnchor.constraint(equalTo: view.heightAnchor),
            ])
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

Answer 2

View Controller Lifecycle - slight difference between an Xcode Playground and an Xcode Project ...

In this Xcode playground, notice the view controller's view bounds don't yet match the simulator size in viewDidLoad (). The simulator seems to default to iPad size but then display at iPhone size. In an Xcode project however, this isn't the case — you can get the current simulator bounds in viewDidLoad() .

In either case, a better place to position your subviews is in viewDidLayoutSubviews() .

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {

    var yellowView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()
        yellowView.backgroundColor = .yellow
        yellowView.frame = CGRect(x: 0, y: 0, width: 250, height: 250)
        view.addSubview(yellowView)
    }

    override func viewDidLayoutSubviews() {
        yellowView.center =  CGPoint(x: view.bounds.width / 2, y: view.bounds.height / 2)
    }
}

let vc = MyViewController()
PlaygroundPage.current.liveView = vc

Answer 3

像这样：

newView.center = self.view.center