Check for class existence in Swift

Question

I want to use NSURLQueryItem in my Swift iOS app. However, that class is only available since iOS 8, but my app should also run on iOS 7. How would I check for class existence in Swift?

In Objective-C you would do something like:

if ([NSURLQueryItem class]) {
    // Use NSURLQueryItem class
} else {
    // NSURLQueryItem is not available
}

Related to this question is: How do you check for method or property existence of an existing class?

There is a nice section in https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/AdvancedAppTricks/AdvancedAppTricks.html#//apple_ref/doc/uid/TP40007072-CH7-SW4 called Supporting Multiple Versions of iOS, which explains different techniques for Objective-C. How can these be translated to Swift?

Check out this answer, it worked for me: http://stackoverflow.com/a/24956190/84745 — s4y, Aug 16 '14 at 19:31

tounaobun · Accepted Answer · 2015-06-13T12:49:26.133

16

Swift 2.0 provides us with a simple and natural way to do this.It is called API Availability Checking.Because NSURLQueryItem class is only available since iOS8.0,you can do in this style to check it at runtime.

    if #available(iOS 8.0, *) {
        // NSURLQueryItem is available

    } else {
        // Fallback on earlier versions
    }

edited Jun 13 '15 at 12:49

answered Jun 13 '15 at 11:57

tounaobun

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does this work for classes which are platform dependant, eg HealthKit? – lewis Apr 23 '19 at 11:36

score 15 · Answer 2 · answered Feb 13 '15 at 17:44

15

Simplest way I know of

if NSClassFromString("NSURLQueryItem") != nil {
    println("NSURLQueryItem exists")
}else{
    println("NSURLQueryItem does not exists")
}

answered Feb 13 '15 at 17:44

Sean

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4

While this solution works fine with debug settings, but it fails when the app build with release settings. – Aleksejs Mjaliks Mar 27 '15 at 13:56

score 11 · Answer 3 · answered Dec 31 '14 at 20:46

Try this:

if objc_getClass("NSURLQueryItem") != nil {
   // iOS 8 
} else {
   // iOS 7
}

I've also done it like this too:

if let theClass: AnyClass = NSClassFromString("NSURLQueryItem") {
    // iOS 8
} else {
    // iOS 7
}

Or, you can also check system version like so, but this isn't the best practice for iOS dev - really you should check if a feature exists. But I've used this for a few iOS 7 hacks... pragmatism over purity.

    switch UIDevice.currentDevice().systemVersion.compare("8.0.0", options: NSStringCompareOptions.NumericSearch) {
    case .OrderedSame, .OrderedDescending:
        iOS7 = false
    case .OrderedAscending:
        iOS7 = true
    }

That "if let theClass" was most useful in my case, where I first need to check if 3rd party class exists and then use it. — JOM, Jan 05 '16 at 11:48

Check for class existence in Swift

3 Answers3

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