Question

What am I missing here:

+ (id) JSONObjectWithData:(NSData *)data {
#if __IPHONE_OS_VERSION_MAX_ALLOWED < 50000 
    //iOS < 5 didn't have the JSON serialization class
    return [data objectFromJSONData]; //JSONKit
#else      
    NSError *jsonParsingError = nil;
    id jsonObject = [NSJSONSerialization JSONObjectWithData:data options:0   error:&jsonParsingError];
    return jsonObject;
#endif
}

I’m compiling on base SDK 5.0, deployment version is 4.0. When I run it on an iPhone 3G with 4.2.1 I get …..

dyld: Symbol not found: _OBJC_CLASS_$_NSJSONSerialization

Crash on startup….

Answer 1

#if __IPHONE_OS_VERSION_MAX_ALLOWED < 50000 is evaluated on compile time. If you compile your code with the iOS 5 SDK the condition will be false. And the NSJSONSerialization code will be used anyway.

You should check if the NSJSONSerialization class exists. Like this:

+ (id) JSONObjectWithData:(NSData *)data {
    Class jsonSerializationClass = NSClassFromString(@"NSJSONSerialization");
    if (!jsonSerializationClass) {
        //iOS < 5 didn't have the JSON serialization class
        return [data objectFromJSONData]; //JSONKit
    }
    else {
        NSError *jsonParsingError = nil;
        id jsonObject = [NSJSONSerialization JSONObjectWithData:data options:0   error:&jsonParsingError];
        return jsonObject;
    }
    return nil;
}