如果你想查看WatchOS。

斯威夫特

let watchOSVersion = WKInterfaceDevice.currentDevice().systemVersion
print("WatchOS version: \(watchOSVersion)")

objective - c

NSString *watchOSVersion = [[WKInterfaceDevice currentDevice] systemVersion];
NSLog(@"WatchOS version: %@", watchOSVersion);

对于iOS，请尝试:

var systemVersion = UIDevice.current.systemVersion

对于OS X，尝试:

var systemVersion = NSProcessInfo.processInfo().operatingSystemVersion

如果你只是想检查用户是否至少运行了一个特定的版本，你也可以使用以下Swift 2功能，它适用于iOS和OS X:

if #available(iOS 9.0, *) {
    // use the feature only available in iOS 9
    // for ex. UIStackView
} else {
    // or use some work around
}

但不建议检查操作系统版本。最好检查您想要使用的功能在设备上是否可用，而不是比较版本号。 对于iOS，如前所述，你应该检查它是否响应选择器; 如:

if (self.respondsToSelector(Selector("showViewController"))) {
    self.showViewController(vc, sender: self)
} else {
    // some work around
}

在Swift 2及更高版本中，检查系统版本(以及许多其他版本)最简单和最简单的方法是:

if #available(iOS 9.0, *) { // check for iOS 9.0 and later

}

此外，使用#available你可以检查这些版本:

iOS
iOSApplicationExtension
macOS
macOSApplicationExtension
watchOS
watchOSApplicationExtension
tvOS
tvOSApplicationExtension
swift

快4.倍

func iOS_VERSION_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: NSString.CompareOptions.numeric) == ComparisonResult.orderedSame
}

func iOS_VERSION_GREATER_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: NSString.CompareOptions.numeric) == ComparisonResult.orderedDescending
}

func iOS_VERSION_GREATER_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: NSString.CompareOptions.numeric) != ComparisonResult.orderedAscending
}

func iOS_VERSION_LESS_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: NSString.CompareOptions.numeric) == ComparisonResult.orderedAscending
}

func iOS_VERSION_LESS_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: NSString.CompareOptions.numeric) != ComparisonResult.orderedDescending
}

用法:

if iOS_VERSION_GREATER_THAN_OR_EQUAL_TO(version: "11.0") {
    //Do something!
}

附:KVISH回答翻译成Swift 4。x和重命名函数，因为我专门为iOS应用程序使用这个片段。

我做了帮助函数，从下面的链接转移到swift:

我们如何通过程序检测设备运行的iOS版本?

func SYSTEM_VERSION_EQUAL_TO(version: String) -> Bool {
    return UIDevice.currentDevice().systemVersion.compare(version,
        options: NSStringCompareOptions.NumericSearch) == NSComparisonResult.OrderedSame
}

func SYSTEM_VERSION_GREATER_THAN(version: String) -> Bool {
    return UIDevice.currentDevice().systemVersion.compare(version,
        options: NSStringCompareOptions.NumericSearch) == NSComparisonResult.OrderedDescending
}

func SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.currentDevice().systemVersion.compare(version,
        options: NSStringCompareOptions.NumericSearch) != NSComparisonResult.OrderedAscending
}

func SYSTEM_VERSION_LESS_THAN(version: String) -> Bool {
    return UIDevice.currentDevice().systemVersion.compare(version,
        options: NSStringCompareOptions.NumericSearch) == NSComparisonResult.OrderedAscending
}

func SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.currentDevice().systemVersion.compare(version,
        options: NSStringCompareOptions.NumericSearch) != NSComparisonResult.OrderedDescending
}

它可以这样使用:

SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO("7.0")

斯威夫特4.2

func SYSTEM_VERSION_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == .orderedSame
}

func SYSTEM_VERSION_GREATER_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == .orderedDescending
}

func SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) != .orderedAscending
}

func SYSTEM_VERSION_LESS_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == .orderedAscending
}

func SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) != .orderedDescending
}

马特·汤普森分享了一种非常简便的方法

switch UIDevice.currentDevice().systemVersion.compare("8.0.0", options: NSStringCompareOptions.NumericSearch) {
case .OrderedSame, .OrderedDescending:
    println("iOS >= 8.0")
case .OrderedAscending:
    println("iOS < 8.0")
}