what's the difference between single key and keypath?

Question

as shown in this page

[self setValue:[NSNumber numberWithInt:intValue] forKey:@"myObject.value"];

The answer was that "of course, it's a key path not a single key", What does that mean?

Answer 1

A key is a string that identifies a property of an object. A key path is a list of keys separated by dots, used to identify a nested property.

Here's an example. If an object person has a property address, which itself has a property town you could get the town value in two steps using keys:

id address = [person valueForKey:@"address"];
id town = [address valueForKey:@"town"];

or in one step using a keyPath:

id town = [person valueForKeyPath:@"address.town"];

Have a look at Apple's docs on Key-Value Coding for further details.