when 相当于 at that time 强调时间点里干的事情；

while 相当于during that time 强调时间段内干的事情。

as 相当于“一边...，一边” 强调两个动作同时发生。

a. When the teacher came in, we were talking.
b. While we were talking, the teacher came in.
c. They were singing as we were dancing.

网友的理解基本正确。长动词改为延续性动词。短动词改为非延续性动词。

记住while和when，as的区别，延续性和非延续性的区别就好了。

你这样记比较复杂，容易混乱。

He was sleeping when I arrived. 

I arrived when he was sleeping. 

如果你只记忆形式的话，不仅使用时极不方便，而且不能理解其真实含义。

比如上面你写的例句，我想你要么认为这两句意思完全一样，要么认为完全不一样。

关于 when, while, as的用法区别，请阅读以下链接：

http://www.yygrammar.com/Article/200802/154.html

when, as, while

when 表示从句动作与主句动作同时发生，或先于主句动作。While表示从句的动作与主句同时发生，并有延续之意，所以这种从句的动作往往是延续性的。As表示从句动作与主句动作并行发生，所以常译为“边……边……”；有时也可表示从句动作比主句动作早些发生。从时间上来说，when指一段时间或一点时间，while只能指一段时间，as指一段时间。

【例句】

When Sally arrived, I was preparing lunch.

While Cathy was doing the washing-up, she was planning her holiday.

The workers shouted slogans as they passed the square.