How do I get the App version and build number using Swift?

Updated for Swift 3.0

The NS-prefixes are now gone in Swift 3.0 and several properties/methods have changed names to be more Swifty. Here's what this looks like now:

extension Bundle {
    var releaseVersionNumber: String? {
        return infoDictionary?["CFBundleShortVersionString"] as? String
    }
    var buildVersionNumber: String? {
        return infoDictionary?["CFBundleVersion"] as? String
    }
}

Bundle.main.releaseVersionNumber
Bundle.main.buildVersionNumber

Old Updated Answer

I've been working with Frameworks a lot since my original answer, so I wanted to update my solution to something that is both simpler and much more useful in a multi-bundle environment:

extension NSBundle {

    var releaseVersionNumber: String? {
        return self.infoDictionary?["CFBundleShortVersionString"] as? String
    }

    var buildVersionNumber: String? {
        return self.infoDictionary?["CFBundleVersion"] as? String
    }

}

Now this extension will be useful in apps to identify both the main bundle and any other included bundles (such as a shared framework for extension programming or third frameworks like AFNetworking), like so:

NSBundle.mainBundle().releaseVersionNumber
NSBundle.mainBundle().buildVersionNumber

// or...

NSBundle(URL: someURL)?.releaseVersionNumber
NSBundle(URL: someURL)?.buildVersionNumber

---

Original Answer

I wanted to improve on some of the answers already posted. I wrote a class extension that can be added to your tool chain to handle this in a more logical fashion.

extension NSBundle {

class var applicationVersionNumber: String {
    if let version = NSBundle.mainBundle().infoDictionary?["CFBundleShortVersionString"]

as? String { return version } return "Version Number Not Available" }

class var applicationBuildNumber: String {
    if let build = NSBundle.mainBundle().infoDictionary?["CFBundleVersion"] as? String {
        return build
    }
    return "Build Number Not Available"
}

}

So now you can access this easily by:

let versionNumber = NSBundle.applicationVersionNumber

EDIT

Updated for Swift 4.2

let appVersion = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String

EDIT

As pointed out by @azdev on the new version of Xcode you will get a compile error for trying my previous solution, to solve this just edit it as suggested to unwrap the bundle dictionary using a !

let nsObject: AnyObject? = Bundle.main.infoDictionary!["CFBundleShortVersionString"]

End Edit

Just use the same logic than in Objective-C but with some small changes

//First get the nsObject by defining as an optional anyObject
let nsObject: AnyObject? = NSBundle.mainBundle().infoDictionary["CFBundleShortVersionString"]

//Then just cast the object as a String, but be careful, you may want to double check for nil
let version = nsObject as! String