swift - 如何在编码函数中修复此 if/let 语句？

Question

class story: NSObject, NSCoding {

    var label = UILabel()
    var title = String()
    var index = Int()
    var cover = UIImage()
    var frame = CGRect()

    func encode(with aCoder: NSCoder) {
        if let label = label { aCoder.encodeObject(label, forKey: "label") as! UILabel }
        if let title = title { aCoder.encodeObject(title, forKey: "title") }
        if let index = index { aCoder.encodeObject(index, forKey: "index") }
        if let cover = cover { aCoder.encodeObject(cover, forKey: "cover") }
        if let frame = frame { aCoder.encodeObject(frame, forKey: "frame") }
    }

    required convenience init?(coder aDecoder: NSCoder) {
        self.init()
        self.label = aDecoder.decodeObject(forKey: "label") as! UILabel
        self.title = aDecoder.decodeObject(forKey: "title") as! String
        self.index = aDecoder.decodeObject(forKey: "index") as! Int
        self.cover = aDecoder.decodeObject(forKey: "cover") as! UIImage
        self.frame = aDecoder.decodeObject(forKey: "frane") as! CGRect
    }

    func formatStorySize() {
        let newWidth = self.frame.width * 0.8
        let newHeight = self.frame.height * 0.9
        let newX = self.frame.origin.x + newWidth / 2
        let newY = self.frame.origin.y + newHeight / 2

        self.frame = CGRect(x: newX, y: newY, width: newWidth, height: newHeight)
    }

    func addLabel(text: String) -> UILabel {
        let label = UILabel()
        label.backgroundColor = UIColor.white
        label.text = text
        label.textAlignment = .center
        let width = self.frame.width
        let height: CGFloat = 40
        let xPos = self.frame.origin.x
        let yPos = self.frame.origin.y + self.frame.height - height
        label.frame = CGRect(x: xPos, y: yPos, width: width, height: height)
        self.title = label.text!
        return(label)
    }
}

有人告诉我，为了将一组自定义类实例保存到 UserDefaults，我必须添加编码函数和解码函数。但是，我收到错误:

Initializer for conditional binding must have Optional type, not 'UILabel'

在编码函数中的第一行之后，以及所有连续行之后的类似错误。我需要更改什么？

Answer 1

None 这些属性是可选的，因此您在 encode 方法中根本不需要 if let。

func encode(with aCoder: NSCoder) {
    aCoder.encode(label, forKey: "label")
    aCoder.encode(title, forKey: "title")
    aCoder.encode(index, forKey: "index")
    aCoder.encode(cover, forKey: "cover")
    aCoder.encode(frame, forKey: "frame")
}

解决该问题后，您不应使用 UserDefaults 来保存数据。将编码数据写入文件。