Detect BOOL availability to support multiple iOS versions?

Question

I am trying to find out how one can detect if an external BOOL is available so that I can support iOS 7 and 8. New in iOS 8 is a BOOL you can use to find out if Reduce Transparency is enabled, and I want to implement that check in an if statement, but this will crash on iOS 7 without first checking if the extern BOOL is available. I was surprised I could not find the answer from my web searches.

Here is the BOOl definition:

UIKIT_EXTERN BOOL UIAccessibilityIsReduceTransparencyEnabled() NS_AVAILABLE_IOS(8_0);

And the location I'm using it:

if (UIAccessibilityIsReduceTransparencyEnabled()) {
    NSLog(@"transparency is disabled");
}

Answer 1

Please read the SDK Compatibility Guide.

What you need to do is check if the function UIAccessibilityIsReduceTransparencyEnabled exists:

if (UIAccessibilityIsReduceTransparencyEnabled != NULL) {
    // function exists, use it
    if (UIAccessibilityIsReduceTransparencyEnabled()) {
        NSLog(@"transparency is disabled");
    }
} else {
    // function doesn't exist, do something else
}