usage - What's the difference between [V-ながら][V2] and [V-ている]間 [V2]?

What's the difference between [V-ながら][V2] and [V-ている]間[V2] ?

For example, is there any difference in nuance between these 2 sentences:

1. 
   

   トムはテレビを見てる間勉強していた

   
   


2. 
   
   

   トムはテレビを見ながら勉強していた

   
   

Answer

田中さんは、AをしながらBをします

means that Mr Tanaka primarily does A. Incidentally, he also does B.

田中さんは、友達と飲みながら通常会話を学びます。 Mr Tanaka learns casual conversation skills while drinking with his friends.

The main action is drinking, it's the whole context. Incidentally, it's also the unrelated opportunity to practice conversation.

Some grammar books would tell you that "ながら" is similar to "のに", to show that it's linking two different actions, and does not concern time (even though they are simultaneous):

テレビを見ながら、宿題に集中する

is almost "even though I'm watching the telly, I'm concentrating on my homework." It's a kind of opposition showing that the two actions are not logically connected.