Objective-C: Coding for various iOS versions

Question

I was wondering whether it is possible / how it is possible to code a class so it can be run on different iOS versions in Objective-C. For example the VisualEffectView is only available in iOS8 and after. Is it possible to declare a VisualEffectView if iOS >= 8 and UIView if not? If so can this be done within a header file?

I want to create an alert box to appear on top of a view controller when a save completes or error occurs. Depending on the iOS version it would be nice if a fancy blurry view is used or just a flat UIView.

What language are you programming in? It makes a big difference. — matt, May 05 '15 at 16:00
You need to read the [SDK Compatibility Guide](https://developer.apple.com/library/prerelease/ios/documentation/DeveloperTools/Conceptual/cross_development/Introduction/Introduction.html). — rmaddy, May 05 '15 at 16:01
@matt The OP mentioned "a header file" so I'm assuming Objective-C. — rmaddy, May 05 '15 at 16:02

score 1 · Answer 1 · answered May 05 '15 at 16:02

1

In an if statement, use NSClassFromString. You'll discover immediately that UIVisualEffectView doesn't exist when it returns nil, and thus you can take one branch if it exists and another if it doesn't:

if (!NSClassFromString(@"UIVisualEffectView")) {
    // ... use UIView ...
} else {
    // ... use UIViewVisualEffectView ... {
}

answered May 05 '15 at 16:02

matt

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And for a more extensive list of conditional coding techniques for backwards compatibility, see my book: http://www.apeth.com/iOSBook/ch09.html#_device_architecture_and_conditional_code – matt May 05 '15 at 16:03

score 1 · Answer 2 · answered May 05 '15 at 16:39

1

As of iOS 5 you can the following syntax.

if ([UIVisualEffectView class]) {
    // Create and use a UIVisualEffectView
}

This will occasionally bite you, NSMapTable is available in iOS versions prior to iOS 6, but was only "officially" available in iOS 6. When attempting to use it in iOS 5 there was some sporadic undocumented behavior.

answered May 05 '15 at 16:39

Tim Johnsen

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Won't this crash on an iOS 7 device because it doesn't have the UIVisualEffectView class? – rounak May 05 '15 at 17:24
Nope, using this syntax is safe to check for class availability in iOS 5 and above. – Tim Johnsen May 05 '15 at 17:27

score 0 · Answer 3 · answered May 05 '15 at 17:24

0

As many have suggested, you can use the NSClassFromString function to find out at run time if the OS version has the class. If it doesn't (that is iOS 7 devices) and you still want live blurring, I'd recommend LiveFrost.

answered May 05 '15 at 17:24

rounak

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Objective-C: Coding for various iOS versions

3 Answers3