如何使用.center将子视图放置在父视图的中心？(How to place a subview in the center of parent view using .center?)

我有两个子视图：紫色的属于一个主视图，它的语法很棒：

sSubview.center = view.center

橙色的属于紫色视图，相同的语法不能正确放置在中心。你能看看我的错误在哪里吗？

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, y: 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) }

}

这里是一个屏幕：

I have two subviews: the purple one belongs to a main view and it works wonderful with the syntax:

sSubview.center = view.center

The orange one belongs to the purple view and the same syntax doesn't place it correctly in the center. Could you see where my mistake is?

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, y: 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) }

}

Here is a screen: