swift如何发送＆nil到func？

Question

func setupCircular(circularLayer:inout CAShapeLayer?){ 
    if (circularLayer == nil) { 
     circularLayer = CAShapeLayer() 
    }else{ 

    } 
} 
setupCircular(circularLayer: &nil) 

怎么写？

Answer 1

您不能使用的值作为斯威夫特的inout参数。您需要创建一个类型为CAShapeLayer的变量，并为其指定一个nil值，并将其用作函数的输入参数。

func setupCircular(circularLayer:inout CAShapeLayer?){ 
    if (circularLayer == nil) { 
     circularLayer = CAShapeLayer() 
    }else{ 

    } 
} 

var circ: CAShapeLayer? = nil 
setupCircular(circularLayer: &circ)