虽然我更喜欢@Francescu的方式(使用带有静态属性的结构体)，但你也可以定义全局常量和变量:

let someNotification = "TEST"

但是请注意，与局部变量/常量和类/结构属性不同，全局变量是隐式惰性的，这意味着它们在第一次访问时被初始化。

建议阅读:全局变量和局部变量，以及Swift中的全局变量都不是变量

对于通知，你可以使用扩展，像这样:

extension Notification.Name {
    static let testNotification = "kTestNotification"
}

然后像NotificationCenter.default.post那样使用它(名称:.testNotification，对象:nil)

向苹果学习是最好的方法。

例如，苹果的键盘通知:

extension UIResponder {

    public class let keyboardWillShowNotification: NSNotification.Name

    public class let keyboardDidShowNotification: NSNotification.Name

    public class let keyboardWillHideNotification: NSNotification.Name

    public class let keyboardDidHideNotification: NSNotification.Name

}

现在我向苹果学习:

extension User {
    /// user did login notification
    static let userDidLogInNotification = Notification.Name(rawValue: "User.userDidLogInNotification")
}

更重要的是，NSAttributedString.Key.foregroundColor:

extension NSAttributedString {

    public struct Key : Hashable, Equatable, RawRepresentable {

        public init(_ rawValue: String)

        public init(rawValue: String)
    }
}

extension NSAttributedString.Key {

    /************************ Attributes ************************/

    @available(iOS 6.0, *)
    public static let foregroundColor: NSAttributedString.Key // UIColor, default blackColor

}

现在我向苹果学习:

extension UIFont {

    struct Name {

    }

}

extension UIFont.Name {

    static let SFProText_Heavy = "SFProText-Heavy"
    static let SFProText_LightItalic = "SFProText-LightItalic"
    static let SFProText_HeavyItalic = "SFProText-HeavyItalic"

}

用法:

let font = UIFont.init(name: UIFont.Name.SFProText_Heavy, size: 20)

向苹果学习是每个人都可以做的事情，可以很容易地提高你的代码质量。

考虑枚举。这些可以在逻辑上分解为单独的用例。

enum UserDefaultsKeys: String {
    case SomeNotification = "aaaaNotification"
    case DeviceToken = "deviceToken"
}

enum PhotoMetaKeys: String {
    case Orientation = "orientation_hv"
    case Size = "size"
    case DateTaken = "date_taken"
}

一个独特的好处发生在你有一个互斥选项的情况下，比如:

for (key, value) in photoConfigurationFile {
    guard let key = PhotoMetaKeys(rawvalue: key) else {
        continue // invalid key, ignore it
    }
    switch (key) {
    case.Orientation: {
        photo.orientation = value
    }
    case.Size: {
        photo.size = value
    }
    }
}

在本例中，您将收到一个编译错误，因为您没有处理PhotoMetaKeys.DateTaken的情况。

颜色

extension UIColor {
    static var greenLaPalma: UIColor {
        return UIColor(red:0.28, green:0.56, blue:0.22, alpha:1.00)
    }
}

字体

enum CustomFontType: String {
    case avenirNextRegular = "AvenirNext-Regular",
    avenirDemiBold = "AvenirNext-DemiBold"
}

extension UIFont {
    static func getFont(with type: CustomFontType, size: CGFloat) -> UIFont {
        let font = UIFont(name: type.rawValue, size: size)!

        return font
    }
}

对于其他-一切都与接受的答案相同。

结构作为命名空间

在我看来，处理这类常量的最好方法是创建一个Struct。

struct Constants {
    static let someNotification = "TEST"
}

然后，例如，在你的代码中这样调用它:

print(Constants.someNotification)

嵌套

如果你想要一个更好的组织，我建议你使用分段子结构

struct K {
    struct NotificationKey {
        static let Welcome = "kWelcomeNotif"
    }

    struct Path {
        static let Documents = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as String
        static let Tmp = NSTemporaryDirectory()
    }
}

然后您可以使用实例K.Path.Tmp

现实世界的例子

这只是一个技术解决方案，在我的代码中的实际实现看起来更像:

struct GraphicColors {

    static let grayDark = UIColor(0.2)
    static let grayUltraDark = UIColor(0.1)

    static let brown  = UIColor(rgb: 126, 99, 89)
    // etc.
}

and

enum Env: String {
    case debug
    case testFlight
    case appStore
}

struct App {
    struct Folders {
        static let documents: NSString = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString
        static let temporary: NSString = NSTemporaryDirectory() as NSString
    }
    static let version: String = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as! String
    static let build: String = Bundle.main.object(forInfoDictionaryKey: "CFBundleVersion") as! String

    // This is private because the use of 'appConfiguration' is preferred.
    private static let isTestFlight = Bundle.main.appStoreReceiptURL?.lastPathComponent == "sandboxReceipt"

    // This can be used to add debug statements.
    static var isDebug: Bool {
        #if DEBUG
        return true
        #else
        return false
        #endif
    }

    static var env: Env {
        if isDebug {
            return .debug
        } else if isTestFlight {
            return .testFlight
        } else {
            return .appStore
        }
    }
}