Question

我有这个结构：

struct Direction {
    let Left = CGPoint(x: -1, y: 0)
    let Top = CGPoint(x: 0, y: -1)
    let Right = CGPoint(x: 1, y: 0)
    let Down = CGPoint(x: 0, y: 1)

    let TopLeft = CGPoint(x: -1, y: -1)
    let TopRight = CGPoint(x: 1, y: -1)
    let DownLeft = CGPoint(x: -1, y: 1)
    let DownRight = CGPoint(x: 1, y: 1)

    let None = CGPointZero
}

我试着像这样使用它：

class AClass {
    var point:CGPoint!

    init() {
        self.point = Direction.None // Direction.Type does not have a member named 'None'
    }
}

我已尝试将.None设为var和public，但我似乎并不理解这一点。

Answer 1

似乎您正在尝试使用结构的静态成员，但您只声明了实例成员。将static添加到所有媒体资源。

struct Direction {
    static let Left = CGPoint(x: -1, y: 0)
    static let Top = CGPoint(x: 0, y: -1)
    static let Right = CGPoint(x: 1, y: 0)
    static let Down = CGPoint(x: 0, y: 1)

    static let TopLeft = CGPoint(x: -1, y: -1)
    static let TopRight = CGPoint(x: 1, y: -1)
    static let DownLeft = CGPoint(x: -1, y: 1)
    static let DownRight = CGPoint(x: 1, y: 1)

    static let None = CGPointZero
}

Answer 2

如果@ Kirsteins的假设是正确的，并且您需要将结构值用作静态属性，那么可以采用另一种方法来实现相同的结果，但在我看来更好的方式：使用枚举。

但是swift枚举只接受字符，字符串和数字作为原始值，而CGPoint则由一对浮点数组成。幸运的是，swift使我们能够使用字符串文字来指定该对，然后将其转换为CGFloat：

extension CGPoint : StringLiteralConvertible {
    public static func convertFromStringLiteral(value: StringLiteralType) -> CGPoint {
        return CGPointFromString(value)
    }

    public static func convertFromExtendedGraphemeClusterLiteral(value: StringLiteralType) -> CGPoint {
        return convertFromStringLiteral(value)
    }
}

此扩展程序允许我们按如下方式初始化CGFloat：

let point: CGPoint = "{1, -3}"

在我们手中，我们可以按如下方式定义枚举：

enum Direction : CGPoint {
    case Left = "{-1, 0}"
    case Top = "{0, -1}"
    case Right = "{1, 0}"
    case Down = "{0, 1}"

    case TopLeft = "{-1, -1}"
    case TopRight = "{1, -1}"
    case DownLeft = "{-1, 1}"
    case DownRight = "{1, 1}"

    case None = "{0, 0}"
}

并在您的代码段中使用：

class AClass {
    var point:CGPoint!

    init() {
        self.point = Direction.None.toRaw()
    }
}

Swift结构不能找到成员

2 个答案: