it's nice doing sth.
做了某件事真好.(事情已经做完了)
It's nice to do sth.
做某事真好(没有做,即将要做)
例:
Nice to meet you.
(初次见面时说的)
Nice meeting you(临别时说的,已经见面了)
it is nice ( ) (watch) a film with you
这里要看句子的语境,
如果·意思是·期待,则是：
it is nice (to watch) a film with you,期待和你一起看电影
如果·意思是回忆,感概,则是：
it is nice (watching) a film with you,和你一起看电影的感觉真好
供参考