一般来说，最好是询问一个对象是否可以执行给定的选择器，而不是检查版本号来决定它是否必须存在。

当这不是一个选项，你需要在这里有点小心，因为[@"5.0"比较:@"5"选项:NSNumericSearch]返回nsordereddescent这可能不是有意的;我可能期待NSOrderedSame。这至少是一个理论上的问题，在我看来，这是一个值得防范的问题。

同样值得考虑的是，可能会出现无法合理比较的糟糕版本输入。苹果提供了三个预定义的常量NSOrderedAscending, NSOrderedSame和nsordereddescent，但我可以想到一个叫做NSOrderedUnordered的东西的使用，在我不能比较两个东西的情况下，我想返回一个值来指示这个。

更重要的是，苹果有一天会扩展他们的三个预定义常量以允许各种返回值，这是不可能的，这使得比较不明智。

考虑下面的代码。

typedef enum {kSKOrderedNotOrdered = -2, kSKOrderedAscending = -1, kSKOrderedSame = 0, kSKOrderedDescending = 1} SKComparisonResult;

@interface SKComparator : NSObject
+ (SKComparisonResult)comparePointSeparatedVersionNumber:(NSString *)vOne withPointSeparatedVersionNumber:(NSString *)vTwo;
@end

@implementation SKComparator
+ (SKComparisonResult)comparePointSeparatedVersionNumber:(NSString *)vOne withPointSeparatedVersionNumber:(NSString *)vTwo {
  if (!vOne || !vTwo || [vOne length] < 1 || [vTwo length] < 1 || [vOne rangeOfString:@".."].location != NSNotFound ||
    [vTwo rangeOfString:@".."].location != NSNotFound) {
    return SKOrderedNotOrdered;
  }
  NSCharacterSet *numericalCharSet = [NSCharacterSet characterSetWithCharactersInString:@".0123456789"];
  NSString *vOneTrimmed = [vOne stringByTrimmingCharactersInSet:numericalCharSet];
  NSString *vTwoTrimmed = [vTwo stringByTrimmingCharactersInSet:numericalCharSet];
  if ([vOneTrimmed length] > 0 || [vTwoTrimmed length] > 0) {
    return SKOrderedNotOrdered;
  }
  NSArray *vOneArray = [vOne componentsSeparatedByString:@"."];
  NSArray *vTwoArray = [vTwo componentsSeparatedByString:@"."];
  for (NSUInteger i = 0; i < MIN([vOneArray count], [vTwoArray count]); i++) {
    NSInteger vOneInt = [[vOneArray objectAtIndex:i] intValue];
    NSInteger vTwoInt = [[vTwoArray objectAtIndex:i] intValue];
    if (vOneInt > vTwoInt) {
      return kSKOrderedDescending;
    } else if (vOneInt < vTwoInt) {
      return kSKOrderedAscending;
    }
  }
  if ([vOneArray count] > [vTwoArray count]) {
    for (NSUInteger i = [vTwoArray count]; i < [vOneArray count]; i++) {
      if ([[vOneArray objectAtIndex:i] intValue] > 0) {
        return kSKOrderedDescending;
      }
    }
  } else if ([vOneArray count] < [vTwoArray count]) {
    for (NSUInteger i = [vOneArray count]; i < [vTwoArray count]; i++) {
      if ([[vTwoArray objectAtIndex:i] intValue] > 0) {
        return kSKOrderedAscending;
      }
    }
  }
  return kSKOrderedSame;
}
@end

#define _kisiOS7 ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)

if (_kisiOS7) {
            NSLog(@"iOS7 or greater")
} 
else {
           NSLog(@"Less than iOS7");
}

快速的例子，实际工作:

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

不要使用NSProcessInfo，因为它在8.0下不能工作，所以它在2016年之前几乎没用

在您的项目中添加以下Swift代码，并轻松访问iOS版本和设备等信息。

class DeviceInfo: NSObject {

    struct ScreenSize
    {
        static let SCREEN_WIDTH = UIScreen.main.bounds.size.width
        static let SCREEN_HEIGHT = UIScreen.main.bounds.size.height
        static let SCREEN_MAX_LENGTH = max(ScreenSize.SCREEN_WIDTH, ScreenSize.SCREEN_HEIGHT)
        static let SCREEN_MIN_LENGTH = min(ScreenSize.SCREEN_WIDTH, ScreenSize.SCREEN_HEIGHT)
    }

    struct DeviceType
    {
        static let IS_IPHONE_4_OR_LESS =  UIDevice.current.userInterfaceIdiom == .phone && ScreenSize.SCREEN_MAX_LENGTH < 568.0
        static let IS_IPHONE_5 = UIDevice.current.userInterfaceIdiom == .phone && ScreenSize.SCREEN_MAX_LENGTH == 568.0
        static let IS_IPHONE_6 = UIDevice.current.userInterfaceIdiom == .phone && ScreenSize.SCREEN_MAX_LENGTH >= 667.0
        static let IS_IPHONE_6P = UIDevice.current.userInterfaceIdiom == .phone && ScreenSize.SCREEN_MAX_LENGTH == 736.0
        static let IS_IPHONE_X = UIDevice.current.userInterfaceIdiom == .phone && ScreenSize.SCREEN_MAX_LENGTH == 812.0
        static let IS_IPAD      = UIDevice.current.userInterfaceIdiom == .pad && ScreenSize.SCREEN_MAX_LENGTH == 1024.0
        static let IS_IPAD_PRO  = UIDevice.current.userInterfaceIdiom == .pad && ScreenSize.SCREEN_MAX_LENGTH == 1366.0
    }

    struct VersionType{
        static let SYS_VERSION_FLOAT = (UIDevice.current.systemVersion as NSString).floatValue
        static let iOS7 = (VersionType.SYS_VERSION_FLOAT < 8.0 && VersionType.SYS_VERSION_FLOAT >= 7.0)
        static let iOS8 = (VersionType.SYS_VERSION_FLOAT >= 8.0 && VersionType.SYS_VERSION_FLOAT < 9.0)
        static let iOS9 = (VersionType.SYS_VERSION_FLOAT >= 9.0 && VersionType.SYS_VERSION_FLOAT < 10.0)
        static let iOS10 = (VersionType.SYS_VERSION_FLOAT >= 9.0 && VersionType.SYS_VERSION_FLOAT < 11.0)
    }
}

一个在obj - c++ 11中更通用的版本(你可能会用NSString/C函数替换其中的一些东西，但这不是那么冗长。这给了你两种机制。splitSystemVersion为你提供了一个包含所有部分的数组，如果你只是想打开主版本(例如switch([self splitSystemVersion][0]) {case 4: break;案例5:断裂;})。

#include <boost/lexical_cast.hpp>

- (std::vector<int>) splitSystemVersion {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    std::vector<int> versions;
    auto i = version.begin();

    while (i != version.end()) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        versions.push_back(boost::lexical_cast<int>(versionPart));
    }

    return versions;
}

/** Losslessly parse system version into a number
 * @return <0>: the version as a number,
 * @return <1>: how many numeric parts went into the composed number. e.g.
 * X.Y.Z = 3.  You need this to know how to compare again <0>
 */
- (std::tuple<int, int>) parseSystemVersion {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    int versionAsNumber = 0;
    int nParts = 0;

    auto i = version.begin();
    while (i != version.end()) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        int part = (boost::lexical_cast<int>(versionPart));
        versionAsNumber = versionAsNumber * 100 + part;
        nParts ++;
    }

    return {versionAsNumber, nParts};
}


/** Assume that the system version will not go beyond X.Y.Z.W format.
 * @return The version string.
 */
- (int) parseSystemVersionAlt {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    int versionAsNumber = 0;
    int nParts = 0;

    auto i = version.begin();
    while (i != version.end() && nParts < 4) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        int part = (boost::lexical_cast<int>(versionPart));
        versionAsNumber = versionAsNumber * 100 + part;
        nParts ++;
    }

    // don't forget to pad as systemVersion may have less parts (i.e. X.Y).
    for (; nParts < 4; nParts++) {
        versionAsNumber *= 100;
    }

    return versionAsNumber;
}

开始Xcode 9，在Objective-C中:

if (@available(iOS 11, *)) {
    // iOS 11 (or newer) ObjC code
} else {
    // iOS 10 or older code
}

开始Xcode 7，在Swift中:

if #available(iOS 11, *) {
    // iOS 11 (or newer) Swift code
} else {
    // iOS 10 or older code
}

对于版本，您可以指定MAJOR、MINOR或PATCH(参见http://semver.org/的定义)。例子:

iOS 11和iOS 11.0是相同的最小版本 iOS 10, iOS 10.3, iOS 10.3.1是不同的最小版本

您可以为这些系统中的任何一个输入值:

iOS, macOS, watchOS, tvOS

来自我的一个豆荚的真实案例:

if #available(iOS 10.0, tvOS 10.0, *) {
    // iOS 10+ and tvOS 10+ Swift code
} else {
    // iOS 9 and tvOS 9 older code
}

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