swift如何發送＆nil到func？

Question

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

    } 
} 
setupCircular(circularLayer: &nil) 

怎麼寫？

Answer 1

您不能使用的值作爲斯威夫特的inout參數。您需要創建一個類型爲CAShapeLayer的變量，併爲其指定一個nil值，並將其用作函數的輸入參數。

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

    } 
} 

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