Objective-C

Essential? No. Highly recommended? In my opinion yes.

 

No. I always recommend to learn Java first. It teaches OOP well.

 

Are you kidding?

There is nothing inherently better about Java for learning how to write good object-oriented code than any other object-oriented language, like Objective-C, but if you were going to pick a language to specifically learn how to write OO code, Java wouldn't be anywhere near the top of the list.

 

According to Stephen Kochan:

According to Apple:

However... It won't hurt to get acquainted at minima with the C language, alongside with learning objC.

 

Actually Eiffel is a very strong OOP language and framework. It definitely gets your thinking in an OOP manner, though I'm not sure if I would use it for any serious project.

 

Kochan is wrong in my opinion. Good Object Oriented coding is not always the best methodology, neither is procedural coding. So I would learn both C and Objective C. That way you'll be ready for high performance Open GL graphics, apps that crunch numbers, audio processing callbacks, photo filters, and etc. As well as reusable OO UI code.

You can also get into extreme trouble with Objective C if you don't understand the C data types and underpinnings, especially when debugging or reading crash dumps.