ios – 如何使用.center将子视图放在父视图的中心？

sSubview.center = view.center

橙色属于紫色视图,相同的语法不能正确放置在中心.
你能看出我的错误在哪里吗？

Here is my code:

import UIKit

class ViewController: UIViewController {

var sSubview = UIView()
var sLabel = UILabel()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view,typically from a nib.
    view.BACkgroundColor = UIColor.lightGray
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

override func viewDidLayoutSubviews() {

    createSimplestSubview()

}

// First subview

func createSimplestSubview() {
 sSubview = UIView(frame: CGRect(x: 0,y: 0,width: view.frame.width * 0.9,height: view.frame.height * 0.9))
 sSubview.BACkgroundColor = UIColor.purple // just for test,to make it visible
 sSubview.center = view.center // that s pretty easy!

 view.addSubview(sSubview)
 createSimplestLabel()
 }

// Second subview

func createSimplestLabel() {

    sLabel = UILabel(frame: CGRect(x: 0,width: sSubview.frame.width * 0.3,height: sSubview.frame.height * 0.2))
    sLabel.BACkgroundColor = UIColor.orange // just for test,to make it visible
    sLabel.center = sSubview.center
    sLabel.text = "This label has to be centered!"
    sLabel.textAlignment = .center
    sLabel.numberOfLines = 0
    sSubview.addSubview(sLabel)

}

}

这是一个屏幕：