[[[UIDevice currentDevice] systemVersion] floatValue]

我知道现在回答这个问题已经太迟了。我不确定我的方法是否仍然适用于低iOS版本(< 5.0):

NSString *platform = [UIDevice currentDevice].model;

NSLog(@"[UIDevice currentDevice].model: %@",platform);
NSLog(@"[UIDevice currentDevice].description: %@",[UIDevice currentDevice].description);
NSLog(@"[UIDevice currentDevice].localizedModel: %@",[UIDevice currentDevice].localizedModel);
NSLog(@"[UIDevice currentDevice].name: %@",[UIDevice currentDevice].name);
NSLog(@"[UIDevice currentDevice].systemVersion: %@",[UIDevice currentDevice].systemVersion);
NSLog(@"[UIDevice currentDevice].systemName: %@",[UIDevice currentDevice].systemName);

你可以得到以下结果:

[UIDevice currentDevice].model: iPhone
[UIDevice currentDevice].description: <UIDevice: 0x1cd75c70>
[UIDevice currentDevice].localizedModel: iPhone
[UIDevice currentDevice].name: Someones-iPhone002
[UIDevice currentDevice].systemVersion: 6.1.3
[UIDevice currentDevice].systemName: iPhone OS

Marek Sebera的大多数时候都很棒，但如果你像我一样，发现自己需要频繁地检查iOS版本，你就不想一直在内存中运行宏，因为你会遇到非常轻微的减速，尤其是在旧设备上。

相反，你希望将iOS版本作为浮点数计算一次，并将它存储在某个地方。在我的例子中，我有一个GlobalVariables单例类，我使用这样的代码来检查我的代码中的iOS版本:

if ([GlobalVariables sharedVariables].iOSVersion >= 6.0f) {
    // do something if iOS is 6.0 or greater
}

要在应用程序中启用此功能，请使用以下代码(适用于使用ARC的iOS 5+):

GlobalVariables.h:

@interface GlobalVariables : NSObject

@property (nonatomic) CGFloat iOSVersion;

    + (GlobalVariables *)sharedVariables;

@end

GlobalVariables.m:

@implementation GlobalVariables

@synthesize iOSVersion;

+ (GlobalVariables *)sharedVariables {
    // set up the global variables as a static object
    static GlobalVariables *globalVariables = nil;
    // check if global variables exist
    if (globalVariables == nil) {
        // if no, create the global variables class
        globalVariables = [[GlobalVariables alloc] init];
        // get system version
        NSString *systemVersion = [[UIDevice currentDevice] systemVersion];
        // separate system version by periods
        NSArray *systemVersionComponents = [systemVersion componentsSeparatedByString:@"."];
        // set ios version
        globalVariables.iOSVersion = [[NSString stringWithFormat:@"%01d.%02d%02d", \
                                       systemVersionComponents.count < 1 ? 0 : \
                                       [[systemVersionComponents objectAtIndex:0] integerValue], \
                                       systemVersionComponents.count < 2 ? 0 : \
                                       [[systemVersionComponents objectAtIndex:1] integerValue], \
                                       systemVersionComponents.count < 3 ? 0 : \
                                       [[systemVersionComponents objectAtIndex:2] integerValue] \
                                       ] floatValue];
    }
    // return singleton instance
    return globalVariables;
}

@end

Now you're able to easily check the iOS version without running macros constantly. Note in particular how I converted the [[UIDevice currentDevice] systemVersion] NSString to a CGFloat that is constantly accessible without using any of the improper methods many have already pointed out on this page. My approach assumes the version string is in the format n.nn.nn (allowing for later bits to be missing) and works for iOS5+. In testing, this approach runs much faster than constantly running the macro.

希望这能帮助任何经历我的问题!

当前最好的版本，不需要在NSString中处理数字搜索是定义宏(查看原始答案:Check iPhone iOS版本)

这些宏确实存在于github中，参见:https://github.com/carlj/CJAMacros/blob/master/CJAMacros/CJAMacros.h

是这样的:

#define SYSTEM_VERSION_EQUAL_TO(v)                  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)
#define SYSTEM_VERSION_GREATER_THAN(v)              ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)
#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)

像这样使用它们:

if (SYSTEM_VERSION_LESS_THAN(@"5.0")) {
    // code here
}

if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"6.0")) {
    // code here
}

过时版本如下

获取操作系统版本:

[[UIDevice currentDevice] systemVersion]

返回字符串，可以通过转换为int/float

-[NSString floatValue]
-[NSString intValue]

像这样

这两个值(floatValue, intValue)将由于其类型而被剥离，5.0.1将变成5.0或5 (float或int)，为了精确比较，你必须将它分离为int数组 检查接受的答案在这里:检查iPhone iOS版本

NSString *ver = [[UIDevice currentDevice] systemVersion];
int ver_int = [ver intValue];
float ver_float = [ver floatValue];

像这样比较

NSLog(@"System Version is %@",[[UIDevice currentDevice] systemVersion]);
NSString *ver = [[UIDevice currentDevice] systemVersion];
float ver_float = [ver floatValue];
if (ver_float < 5.0) return false;

对于Swift 4.0语法

下面的例子只是检查设备是否为iOS11或更高版本。

let systemVersion = UIDevice.current.systemVersion
if systemVersion.cgFloatValue >= 11.0 {
    //"for ios 11"
  }
else{
   //"ios below 11")
  }

更新

在iOS 8中，我们可以在NSProcessInfo上使用新的isOperatingSystemAtLeastVersion方法

   NSOperatingSystemVersion ios8_0_1 = (NSOperatingSystemVersion){8, 0, 1};
   if ([[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:ios8_0_1]) {
      // iOS 8.0.1 and above logic
   } else {
      // iOS 8.0.0 and below logic
   }

注意，这会在iOS 7上崩溃，因为该API在iOS 8之前并不存在。如果您支持iOS 7及以下版本，则可以安全地使用

if ([NSProcessInfo instancesRespondToSelector:@selector(isOperatingSystemAtLeastVersion:)]) {
  // conditionally check for any version >= iOS 8 using 'isOperatingSystemAtLeastVersion'
} else {
  // we're on iOS 7 or below
}

原始答案iOS < 8

为了完整起见，以下是苹果在iOS 7 UI过渡指南中提出的另一种方法，其中包括检查基础框架版本。

if (floor(NSFoundationVersionNumber) <= NSFoundationVersionNumber_iOS_6_1) {
   // Load resources for iOS 6.1 or earlier
} else {
   // Load resources for iOS 7 or later
}

要获得分隔主版本和次版本的更具体版本号信息:

NSString* versionString = [UIDevice currentDevice].systemVersion;
NSArray* vN = [versionString componentsSeparatedByString:@"."];

数组vN将以字符串形式包含主版本和次版本，但如果您想进行比较，版本号应该存储为数字(int)。你可以添加这段代码将它们存储在c数组* versionNumbers中:

int versionNumbers[vN.count];
for (int i = 0; i < sizeof(versionNumbers)/sizeof(versionNumbers[0]); i++)
    versionNumbers[i] = [[vN objectAtIndex:i] integerValue];

*这里使用的c数组更简洁的语法。