How do I know what IOS is being used, when running my iPhone app?

Question

Since the launch of IOS 5, I have had to make some changes to my app that only apply when IOS 5 is being used. How can I tell when launching my app whther the user is using IOS 5 or IOS 4 or earlier?

Answer 1

if([[[UIDevice currentDevice] systemVersion] compare:@"5.0" options:NSNumericSearch] !=  NSOrderedDescending)
{
   // code here
}
else 
{
  // code here
}

Answer 2

You should probably avoid asking about the system version altogether.

A better design would ask about a specific feature.

For instance: if (NSClassFromString(@"UIPrintInfo")) would tell you if the current device supports the printing API,available in 4.2 or higher.

That way you can plan your code to use a feature if it's available, on not based on the OS version. More on this here - How to check iOS version?

But if you must then -

float version = [[[UIDevice currentDevice] systemVersion] floatValue]; 

Answer 3

Sometime is nice to know which version of iOS is used. But it is better to ask the system if a method exist:

// iOS 5 UINavigationBar backgroundImage
if ([self.navigationBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)]) {
    UIImage *backgroundImage = [UIImage imageNamed:@"titlebar.png"];
    [self.navigationBar setBackgroundImage:backgroundImage forBarMetrics:UIBarMetricsDefault];
}