这里编写的大多数示例代码都将获得额外零版本的意外结果。例如,

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

在iOS“10.3”中，该方法不会在传递版本“10.3.0”时返回true。这样的结果是没有意义的，必须视为同一版本。为了得到准确的比较结果，必须考虑比较版本字符串中所有的数字分量。另外，以大写字母提供全局方法并不是一个好方法。因为我们在SDK中使用的版本类型是String，所以在String中扩展比较功能是有意义的。

要比较系统版本，以下所有示例都可以工作。

XCTAssertTrue(UIDevice.current.systemVersion.isVersion(lessThan: "99.0.0"))
XCTAssertTrue(UIDevice.current.systemVersion.isVersion(equalTo: UIDevice.current.systemVersion))
XCTAssertTrue(UIDevice.current.systemVersion.isVersion(greaterThan: "3.5.99"))
XCTAssertTrue(UIDevice.current.systemVersion.isVersion(lessThanOrEqualTo: "10.3.0.0.0.0.0.0"))
XCTAssertTrue(UIDevice.current.systemVersion.isVersion(greaterThanOrEqualTo: "10.3"))

你可以在我的存储库中查看 https://github.com/DragonCherry/VersionCompare

注:iOS 8.0及以上版本支持。OS X v10.10及以上版本

var majorVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.majorVersion }
var minorVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.minorVersion }
var patchVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.patchVersion }
var myOSVersion:  String { return NSProcessInfo.processInfo().operatingSystemVersionString        }

Swift 3.0+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
}

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
}

根据Matt Thompson的回答，这里有一个带有各自单元测试的方法，可以在iOS 7及以上版本(包括iOS 9，不再让你检查NSFoundationNumber)上与Swift和Objective-c一起工作:

+ (BOOL) isAtLeastOSVersion:(NSString *)osVersion
{
    switch ([[UIDevice currentDevice].systemVersion compare:osVersion options:NSNumericSearch]) {
        case NSOrderedSame:
        case NSOrderedDescending:
            return YES;
        default:
            return NO;
    }
}  

.

@interface ANFakeCurrDevice : NSObject
@property (nonatomic, strong) NSString *systemVersion;
@end
@implementation ANFakeCurrDevice
@end


@implementation MyHelperClassUnitTests

- (void)setUp {
    [super setUp];
}

- (void)tearDown {
    [super tearDown];
}

- (void)test_isAtLeastOSVersion
{
    id deviceMock = [OCMockObject niceMockForClass:[UIDevice class]];
    ANFakeCurrDevice *fakeCurrDevice = [ANFakeCurrDevice new];
    fakeCurrDevice.systemVersion = @"99.9.9";
    [[[deviceMock stub] andReturn:fakeCurrDevice] currentDevice];
    XCTAssertTrue([[UIDevice currentDevice].systemVersion isEqualToString:@"99.9.9"]);

    fakeCurrDevice.systemVersion = @"1.0.1";
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"1"]);
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"1.0"]);
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"1.0.1"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"1.0.2"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"1.1.0"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"2"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"2.0"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"2.0.0"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"2.0.1"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"2.1.0"]);


    fakeCurrDevice.systemVersion = @"8.4.0";
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"7.0.1"]);
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"8"]);
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"8.4"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"8.4.1"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"8.4.2"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"9.0"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"9.0.1"]);
    XCTAssertFalse([ANConstants isAtLeastOSVersion:@"9.0.2"]);
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"8.4"] && ![ANConstants isAtLeastOSVersion:@"9.0"]);

    fakeCurrDevice.systemVersion = @"8.4.1";
    XCTAssertTrue([ANConstants isAtLeastOSVersion:@"8.4"] && ![ANConstants isAtLeastOSVersion:@"9.0"]);
}


@end

let Device = UIDevice.currentDevice()
let iosVersion = NSString(string: Device.systemVersion).doubleValue

let iOS8 = iosVersion >= 8
let iOS7 = iosVersion >= 7 && iosVersion < 8

检查为

if(iOS8)
{

}
else 
{
}