以编程方式为 UILabel 添加约束，用于循环加载动画

Question

我正在尝试以编程方式在我使用 Open Source software 创建的循环加载图像中添加label。我面临的问题是我不知道如何constrain标签，使其包含在圆圈内。我正在尝试将CAShapeLayer与UILabel进行比较，但这不起作用CAShapeLayer因为这不是Storyboard可用的类型。是否有我应该遵循的建议修复？

let circlePathLayer = CAShapeLayer()
var circleRadius: CGFloat = 100.0   
var circleCenter: CGPoint = CGPoint()
func displayStatus() {
    let statusLabel = UILabel(frame: CGRectMake(0, 0, 200, 21))
    statusLabel.center = CGPointMake(160, 284)
    statusLabel.textAlignment = NSTextAlignment.Center
    statusLabel.textColor = UIColor.whiteColor()
    statusLabel.text = "(Up)loading"
    let horizontalConstraint = NSLayoutConstraint(item: statusLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: circlePathLayer, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0) //ERROR 
    self.addConstraint(horizontalConstraint) 
    let verticalConstraint = NSLayoutConstraint(item: statusLabel, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: circlePathLayer, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0) //ERROR
    self.addConstraint(verticalConstraint)
    self.addSubview(statusLabel)
}

Answer 1

删除此代码：

    let horizontalConstraint = NSLayoutConstraint(item: statusLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: circlePathLayer, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0) //ERROR 
self.addConstraint(horizontalConstraint) 
let verticalConstraint = NSLayoutConstraint(item: statusLabel, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: circlePathLayer, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0) //ERROR
self.addConstraint(verticalConstraint)

添加此代码：

对象 C：

- (void)layoutSubviews
{
    [super layoutSubviews];
    statusLabel.center = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds))
}

迅速：

    override func layoutSubviews() {
    super.layoutSubviews()
    statusLabel.center = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidX(self.bounds))
}