on the fly idiom
informal未经准备或较多考虑就开始匆忙做…（往往与其他事情一起进行）
If you do something on the fly, you do it quickly, often while you are doing something else, without preparing and without thinking too much about how it should be done.
This new rule seems to have been created on the fly. 这一新规则似乎未经考虑就匆匆制定了。
computing specialized无需中断一个已经运行的电脑程序（而同时执行其他功能）
without interrupting a computer program that is already running
He had written a program that could translate from Japanese on the fly. 他写了一个程序，可即时翻译日语。