The reason is that we need references to both ProgressBars as arguments to the callback, and at the time the Scale constructor is invoked, they are not all defined yet.

原因在于，我们需要以对两个ProgressBar的引用作为回调的参数，而当Scale构造函数被调用时，它们还没有被定义。

youdao

You need references to show your awareness of prior work.

你需要列出参考文献，以表明你了解前人已经做了什么。

youdao

At the minute DLA is largely self-assessed - claimants do need medical references and evidence, but the form itself is filled in by the claimant.

BBC: Q&A: Universal Credit and the benefits overhaul

In order to conform to such an irresponsibly naive, if not Luddite, view, the Air Force has responded to the veto by rewriting its doctrines, mission requirements and budget requests to delete references to the need for such capabilities.

CENTERFORSECURITYPOLICY: Clinton Policies Would Disarm U.S. Space Capabilit

Throughout the week there has been constant references to the need for entrepreneurs to be the future engine of both developed and developing economies, but this is the first time we are gathering to discuss effective strategies to make this happen.

FORBES: Opening the Pathway Through Entrepreneurship