为了让我们自己能够主动而自然地用出来will be doing这种结构，我们需要挖掘其背后的思维逻辑。先参考一下几个靠谱的来源，看看是怎么解释这个结构的。
外研社引进的《英语在用：剑桥高级英语语法》（作者: Martin Hewings）对will be doing的用法解释：
网站www.englishgrammarsecrets.com的解释：
We can use 'will be doing' to talk about something that will be in progress at a particular moment in the future.
This time next week, I'll be sitting on the beach in Barbados.
I'll be thinking about you all back in the office – and I'll be laughing.
We'll be enjoying ourselves too, boss. We won't be doing any work while you are not here.
We can use 'will be doing' to talk about future events that are fixed or decided.
I'll be visiting your country on a regular basis. In fact, I'm going to be coming next month.
He'll be looking after the factory until we can appoint a new manager.
They'll be thinking about this very carefully over the next few months.
We can use 'will be doing' to predict what is happening now.
Try phoning his hotel. He'll probably still be having breakfast.
They'll be deciding who gets the contract at this very moment. I'm very nervous.
She's not in her office. She'll be having lunch in the canteen.
We can use 'will be doing' to ask extremely politely, and with no pressure, about future plans.
Will you be eating with us this evening?
Will you be needing anything else?
Will they be joining us for dinner?
而UsingEnglish.com网站也有关于will be doing用法的问答，最靠谱的答案有如下：
The modal auxiliary verb will has a number of possible meanings.These include:
certainty – John left an hour ago, so he will be home by now. (The speaker is certain that John is home)
volition (willingness): I’ll carry your bag for you. (The speaker is offering to carry the bag.) Fred will carry your bag for you. (The speaker is offering Fred’s services.)
instant decision: What will I do tomorrow? I know! I’ll go to the zoo. (The speaker decides to go to the zoo at the very moment of speaking – no plans had been made for this visit.)
The most likely meaning in the following sentence is that it is an enquiry about a future certainty, though it could, just, in the right context, be about the person's willingness:
How long will you stay in Bali?
With modal will + a progressive (continuous) form it is possible that the speaker is more concerned with the pure certainty of the action happening than with volitional aspect that might be implied by the use of WILL by itself:
How long will you be staying in Bali?
Some writers claim, with some justification, that the use of modal will + a progressive implies, by its lack of reference to intention, volition or arrangement, a 'casual' future.
简直各有各的说法，很难让人理出个头绪，不过还是《英语在用》更系统和详细些。以《英语在用》为基础，结合其他网站说法，我们可以发现老外对于will be doing结构有个基本的共识：
will be doing说的是previous arrangement（预先安排好的），即在说话前就已经计划好的。
基于以上理解，我们来体会下面两个问句：
When will you be paying back the money?
（询问possible previous arrangement，即在我问这个问题的时候，我假设你已经有计划要还我钱的，现在只是核实一下而已，别无催帐或怀疑之意——是不是显得很礼貌呢？）
Will you be spending your holidays abroad this year?
（询问possible previous arrangement，即在我问这个问题的时候，我假设你已经有计划今年要出国度假，现在只是好奇了解一下是不是这样，即使不是也没关系，这里并不带有我的期望或敦促等情感，没有干涉之意——是不是很礼貌呢？）
而一旦上面句子换成will do结构，就正好带有上面解释中的红色字所表达的情感成分，有干涉别人的嫌疑。
何以为证？
上文中无论《英语在用》还是UsingEnglish.com网站对will do的含义的解释都不够全面，不足以作为依据来判断其与will be doing的区别。所以我们还是要回归英语词典，请看《柯林斯Cobuild高级英语学习词典》对will情态动词的解释，整理后大致有如下四条情感方面的内涵：
1. 意愿
2. 命令
3. 请求
4. 邀请
我们再回到前面两个蓝色的例句，假如换成will do结构 ，有没有多少带有上面四种释义中的某一两种？是不是很明显有某种情感在里头？要么是期待别人如何如何，要么是暗示别人应该如何如何，这些情感因素显然都是在干涉别人的私事，是不礼貌的。
为什么美剧里总爱用will be doing结构，而不用will do结构？
**总 结**
will be doing的基本内涵是说话时已经有了previous arrangement（早期计划）:
既然will be doing是表示早就有计划了，那么在陈述句中自然是用于fixed或decided（很确定）的场合，含有“既定事实”的意义，这显然比will do带有的instant decision（说话时现场决定）更具有确定性。
既然will be doing是表示早就有计划了，那么在问句中自然只是询问这个“早就有了的”计划而已（possible previous arrangement），不带有催促、期望等主观感情，只是在核实纯粹的客观确定性，自然显得比较polite（礼貌）了。
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