How to check if an NSDictionary or NSMutableDictionary contains a key?

Question

I need to check if an dict has a key or not. How?

Answer 1

objectForKey will return nil if a key doesn't exist.

Answer 2

if ([[dictionary allKeys] containsObject:key]) {     // contains key } 

or

if ([dictionary objectForKey:key]) {     // contains object }