doing mainly B, and secondary A
But there are conditions:
1)the actions have to be done by the same subject
2)B is the main action, and A is the secondary action
3)can be used with nouns/adjectives(something is while)
5)if you want to say that you are doing two things at the same time, this is your default
AつつB(incoming in N2 lesson 8!)
This is a classical Japanese particle, now mostly used in literature and formal speech.
Same as ながら, but cannot be used with nouns and adjectives.
B while(within) A
1)the subject of A and B doesn’t have to be the same
2)verb is in ている form
3)can follow nouns and adjectives
4)it doesn’t necessarily mean that actions are occuring at the same time, it mostly mean that B happened at some point of A.
B while A
1)similar to あいだ so it can follow nouns, adjectives, but the verb doesn’t have to be in ている form
2)suggest that A is the best time(or even only time) to do B, unlike 間
3)can be used with ない meaning before A comes, B.
Because of 2) and 3) it is often used when giving orders, suggesting etc.
So if you want to emphasize it is best to do(or bad to not do something) something within a time frame, うち is your choice.
A中(read as ちゅう)
It is a noun suffix, meaning both in the middle of doing something, during, in the middle, under(renovation etc), in progress and while. It is more formal than 間, and doesn’t have the nuance of うち。
often used as a notification like ロード中((in the midst of)loading), ダウンロード中((in the midst of)downloading),出張中(in the midst of)business trip in those cases it has strong nuance of it happening right now, so you can see it when game is updating, or ur smartphone OS etc.
Have you already downloaded it?
I am downloading right now.