conditionally import framework - iphone

Question

well to begin with I'm sure this is a simple question.
I am developing an iPhone app with the iAd Framework, which only runs for iOS 4.0 or higher.
Still, I wanna choose a iPhone OS 3.0 deployment target, which causes everything to crash.
How do I conditionally include the iAd framework?
...I mean, it would be something like:
...if([[UIDevice currentDevice] systemVersion]>=4.0]) #import
Obviously this won't work because I don't know the correct syntax. Also:
How do I conditionally declare an AdView* variable?
How do I conditionally handle this AdView* variable in my implementation file.
If you guys could help me, I will be very well impressed.
Thanks

Answer 1

You don't need to change your include, you need to make the iAd (or any other new framework) linked weakly:
In your target, find iAd in the linked frameworks and change its "Role" from "Required" to "Weak".
To handle the variable conditionally, use NSClassFromString function, like this:
Class AdClass = NSClassFromString(#"ADBannerView");
if(AdClass) {//if the class exists
ADBannerView* myAd = [[AdClass alloc] initWithFrame:CGRectZero];
// do something with the ad
}
If OS is older than iOS 4.0, AdClass will be nil and the code won't execute. Note that using ADBannerView* as the type of the variable shouldn't cause any problems, as it's just a hint for a compiler and is the same as id after compilation.