以编程方式为UILabel添加一个圆形加载动画的约束

Question

我正在尝试在程序中在使用Open Source software创建的循环加载图像中添加一个label。我面临的问题是我不知道如何标签，使其包含在圆圈内。我试图将CAShapeLayer与UILabel进行比较，但这不会起作用，因为CAShapeLayer不是可从Storyboard获得的类型。有没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) 

添加以下代码：

Objectice C：

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

斯威夫特：

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