I just need some new boxers with a comfortable waistband and a button fly.

我就要买几条大短裤，那种裤腰很舒服的，带扣子的前裆的。

youdao

Another way is to have a button that adds new keyword fields on the fly to allow users to add as many keywords as they want.

另一种办法是让按钮随时增加新的关键字，允许用户根据需要添加任意多的关键字。

youdao

The DHTML object model lets you modify on the fly the structure of the page, but all the changes will be lost as soon as you refresh the view by hitting F5 or clicking the browser's refresh button.

DHTML对象模型使你能够随意修改网页的结构，但这一变化在按f 5刷新后全部复原。

youdao

Don't fly by your belly button.

FORBES: Magazine Article

This is a walker which has front legs that adjust on the fly with the press of a button, making it possible for a person to use the walker to help get up and down stairs.

FORBES: Innovation For Accessibility

Therefore you're focused on just the most basic movements -- a common one involves jumping in the air, tapping the other button for the downward kick, and then tapping it again to fly backwards.

ENGADGET