Checking for the "existence" of version-specific global constants and other features?

Question

I am very much new to the iPhone SDK. I just haven't been able to find the right search query to find out how to do this kind of checking for the existence of a new or deprecated feature.

Case in point:

iOS4 deprecates UIKeyboardBoundsUserInfoKey used for checking the height of the keyboard (and moving, scrolling or whatever to adjust for it). I could still use it but I would like to use the new UIKeyboardFrameEndUserInfoKey on 3.2 and above but still fall back to the old one for older 3.x versions.

How do I determine if UIKeyboardFrameEndUserInfoKey (a global constant) is declared and exists? I guess that is what I need to check since I cant check if the Dictionary contains the key if the key is not even defined anywhere in the Frameworks for the current OS version.

Any advice on this kind of version checking would be helpful. I am sure I will run into other things as well.

Answer 1

Getting the Operating System version may be more helpful as it can be adapted for other use cases as well.

[[UIDevice currentDevice] systemVersion];

See here.

It would return a string like @"3.1.2" that you could use to check for version-specific features.

Answer 2

@Martin, here's how I solved it.

// Get the size of the keyboard.
NSValue* aValue = nil;

aValue = [info objectForKey:@"UIKeyboardBoundsUserInfoKey"];
if (!aValue) {
    aValue = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
}

Using a string constant to query the dictionary for the values isn't recommended, usually, but in this case, UIKeyboardBoundsUserInfoKey is from an old version of iOS, so it's never going to change.