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 
{
}  

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")
}

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 osVersion = NSProcessInfo.processInfo().operatingSystemVersion
let versionString = osVersion.majorVersion.description + "." + osVersion.minorVersion.description + "." + osVersion.patchVersion.description
print(versionString)

细节

Xcode 10.2.1 (10E1001)

链接

OperatingSystemVersion

解决方案

extension OperatingSystemVersion {
    func getFullVersion(separator: String = ".") -> String {
        return "\(majorVersion)\(separator)\(minorVersion)\(separator)\(patchVersion)"
    }
}

let os = ProcessInfo().operatingSystemVersion
print(os.majorVersion)          // 12
print(os.minorVersion)          // 2
print(os.patchVersion)          // 0
print(os.getFullVersion())      // 12.2.0

获取系统的当前版本并拆分它。 所以你可以得到大调和小调版本。

let sys_version = UIDevice.current.systemVersion
let all_version = sys_version.components(separatedBy: ".")
print("Major version : \(all_version[0])")
print("Minor version : \(all_version[1])")