在飞行[行驶]中；匆忙地,在百忙中
1.The bird caught a bug on the fly.那鸟在飞行中捉住了一只昆虫.
来自《简明英汉词典》
2.We had so little time to catch the train that we had to eat our lunch on the fly.我们离上火车的时间不多了,所以不得不匆忙地吃午饭.
来自《简明英汉词典》
3.I'll spot you and put on my headlights and catch you on the fly.我一看到你,就打开前灯,慢慢开车,你一面走着就上车了.
来自教父部分