Swift 3.0

我们不需要创建扩展,因为ProcessInfo我们提供了版本信息.您可以看到iOS的示例代码,如下所示.

let os = ProcessInfo().operatingSystemVersion
switch (os.majorVersion, os.minorVersion, os.patchVersion) {
case (8, 0, _):
    print("iOS >= 8.0.0, < 8.1.0")
case (8, _, _):
    print("iOS >= 8.1.0, < 9.0")
case (9, _, _):
    print("iOS >= 9.0.0")
default:
    // this code will have already crashed on iOS 7, so >= iOS 10.0
    println("iOS >= 10.0.0")
}

参考:http://nshipster.com/swift-system-version-checking/

斯威夫特4

func run() {
    let version = OperatingSystemVersion(majorVersion: 11, minorVersion: 0, patchVersion: 0)
    if ProcessInfo.processInfo.isOperatingSystemAtLeast(version) {
        runNewCode()
    } else {
        runLegacyCode()
    }
}

func runNewCode() {
    guard #available(iOS 11.0, *) else {
        fatalError()
    }
    // do new stuff
}

func runLegacyCode() {
    // do old stuff
}

我使这个Singleton用于简单使用,创建了一个IOSVersion.swift文件并添加了这段代码:

import UIKit

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

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

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

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

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

使用 :

IOSVersion.SYSTEM_VERSION_EQUAL_TO("8.0")
IOSVersion.SYSTEM_VERSION_LESS_THAN("8.0")

谢谢@KVISH

编辑Swift 2:

if #available(iOS 9.0, *) {
    //  
} else {
    // 
}

更新:
现在您应该使用Swift 2引入的新可用性检查:
例如,要在编译时检查iOS 9.0或更高版本,请使用以下命令:

if #available(iOS 9.0, *) {
    // use UIStackView
} else {
    // show sad face emoji
}

或者可以与整个方法或类一起使用

@available(iOS 9.0, *)
func useStackView() {
    // use UIStackView
}

欲了解更多信息请参阅本.

运行时检查:

如果您不想要确切的版本但想要使用if检查iOS 9,10或11:

let floatVersion = (UIDevice.current.systemVersion as NSString).floatValue

编辑: 刚刚找到另一种方法来实现这一目标:

let iOS8 = floor(NSFoundationVersionNumber) > floor(NSFoundationVersionNumber_iOS_7_1)
let iOS7 = floor(NSFoundationVersionNumber) <= floor(NSFoundationVersionNumber_iOS_7_1)

如果您使用的是Swift 2并且想要检查操作系统版本以使用某个API,则可以使用新的可用性功能:

if #available(iOS 8, *) {
    //iOS 8+ code here.
}
else {
    //Code for iOS 7 and older versions.
    //An important note: if you use #availability, Xcode will also 
    //check that you don't use anything that was introduced in iOS 8+
    //inside this `else` block. So, if you try to use UIAlertController
    //here, for instance, it won't compile. And it's great.
}

我写了这个答案,因为这是Google在swift 2 check system version查询中的第一个问题.

对于iOS,请尝试:

var systemVersion = UIDevice.current.systemVersion

对于OS X,请尝试:

var systemVersion = NSProcessInfo.processInfo().operatingSystemVersion

如果您只想检查用户是否至少运行了特定版本,您还可以使用以下适用于iOS和OS X的Swift 2功能:

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

但是不建议检查操作系统版本.最好检查设备上是否有可用的功能,而不是比较版本号. 对于iOS,如上所述,您应该检查它是否响应选择器; 例如.:

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

Swift 3.0+的更新

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

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

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

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

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