CATextLayer不可见

Question

我已经实现了一个函数来绘制CATextLayer的文本用法。但绘制后的文字不可见。

这是我的代码：

func addText() -> CATextLayer{
    let rect:CGRect = CGRect(x: 50, y: 600, width: 120, height: 60)
    let myAttributes = [
                        NSFontAttributeName: UIFont(name: "HelveticaNeue-Thin", size:18)!,
                        NSForegroundColorAttributeName: UIColor.black.cgColor
                        ] as [String : Any]
    let myAttributedString = NSAttributedString(string: "TEST STRING", attributes: myAttributes)

    let textLayer = CATextLayer()
    textLayer.bounds = rect
    textLayer.string = myAttributedString
    textLayer.position = CGPoint(x:150,y:400)
    textLayer.alignmentMode = kCAAlignmentCenter
    textLayer.displayIfNeeded()
    return textLayer
}

有谁知道这个问题？