swift - 试图创建一个圆圈 UIImageView 导致它消失

Question

我有一个简单的 UIImageView，试图将它的 cornerRadius 设置为其宽度的一半，从而导致图像消失。 这是我的:

    private let profileImg: UIImageView = {
    let img = UIImageView(image: UIImage(named: "profileplaceholder"))
    img.translatesAutoresizingMaskIntoConstraints = false
    img.heightAnchor.constraint(equalToConstant: 100).isActive = true
    img.widthAnchor.constraint(equalToConstant: 100).isActive = true

    img.layer.borderWidth = 1.0
    img.layer.borderColor = UIColor.appPurple.cgColor
    img.layer.cornerRadius = (img.frame.width / 2)
    img.clipsToBounds = true
    img.layer.masksToBounds = true
    img.contentMode = .scaleAspectFill

    return img
}()

我只是不明白这里出了什么问题，以及为什么图像根本不显示。

Answer 1

问题是在设置 cornerRadius 时没有获得正确的 ImageView 框架。

添加/更改约束后，您可以使用 layoutIfNeeded() 它将强制布局您的 View 。

这段代码对我有用

class ViewController: UIViewController {

    var profileImageView : UIImageView = {
        let img = UIImageView(image: UIImage(named: "0266554465"))

        img.translatesAutoresizingMaskIntoConstraints = false

        img.heightAnchor.constraint(equalToConstant: 300).isActive = true
        img.widthAnchor.constraint(equalToConstant: 300).isActive = true

        img.layoutIfNeeded()
        img.layer.borderWidth = 1.0
        img.layer.cornerRadius = (img.frame.width / 2)
        img.clipsToBounds = true
        return img
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

         self.view.addSubview(self.profileImageView)

        let centerXConstraint = NSLayoutConstraint(item: profileImageView, attribute: NSLayoutConstraint.Attribute.centerX, relatedBy: NSLayoutConstraint.Relation.equal, toItem: view, attribute: NSLayoutConstraint.Attribute.centerX, multiplier: 1, constant: 0)

        let centerYConstraint = NSLayoutConstraint(item: profileImageView, attribute: NSLayoutConstraint.Attribute.centerY, relatedBy: NSLayoutConstraint.Relation.equal, toItem: view, attribute: NSLayoutConstraint.Attribute.centerY, multiplier: 1, constant: 0)

        view.addConstraints([centerXConstraint, centerYConstraint])
    }

}