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自己搭建的MQTT云服务器 - App Inventor 2 中文网 - 清泛IT社区，为创新赋能！
...题：每次打开我的APP后，要手动订阅一遍主题，才能收到ESP32推送的温度消息，显示在一个标签上，每秒钟刷新。但我一旦离开APP的页面，再切换回来时，又要手动订阅一遍，才能在标签上更新推送来的消息。请问这是什么原因...
How to prevent form from submitting multiple times from client side?
... I tried this solution with unobtrusive validation & MVC. The JS gets called first which always return false and then validation is called. So if my form has some validation error the form never gets submitted!!
– bjan
Jun 8 '12 at 12:09
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Does MS SQL Server's “between” include the range boundaries?
...is and the value will be rounded up to midnight the next day.
e.g. to get all values within June 2016 you'd need to run:
where myDateTime between '20160601' and DATEADD(millisecond, -3, '20160701')
i.e.
where myDateTime between '20160601 00:00:00.000' and '20160630 23:59:59.997'
datetime2 and d...
Can I use assert on Android devices?
...t.
You can do
import static junit.framework.Assert.*;
now you can use all the functions like assertTrue, assertEquals, assertNull that are provided in the junit framework.
Be careful not to import the Junit4 framework through eclipse, that would be the org.junit package. You have to use the j...
Declaration/definition of variables locations in ObjectiveC?
Ever since starting to work on iOS apps and objective C I've been really puzzled by the different locations where one could be declaring and defining variables. On one hand we have the traditional C approach, on the other we have the new ObjectiveC directives that add OO on top of that. Could you fo...
Can an ASP.NET MVC controller return an Image?
...Letting the user pass a file name (path) like this means they could potentially access files from anywhere on the server. Might want to warn people not to use it as-is.
– Ian Mercer
Jan 28 '11 at 7:53
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C++ performance challenge: integer to std::string conversion
... val /= 10;
}
return s;
}
This will blow up on systems that disallow unaligned memory accesses (in which case, the first unaligned assignment via *(short*) would cause a segfault), but should work very nicely otherwise.
One important thing to do is to minimize the use of std::string. (I...
Why do people say that Ruby is slow? [closed]
I like Ruby on Rails and I use it for all my web development projects. A few years ago there was a lot of talk about Rails being a memory hog and about how it didn't scale very well but these suggestions were put to bed by Gregg Pollack here.
...
How to compute the similarity between two text documents?
...
If I were to average all of the values outside of the diagonal of 1's, would that be a sound way of getting a single score of how similar the four documents are to each other? If not, is there a better way of determining overall similarity betwe...
What is external linkage and internal linkage?
... a translation unit. This is the source file from your implementation plus all the headers you #included in it.
Internal linkage refers to everything only in scope of a translation unit.
External linkage refers to things that exist beyond a particular translation unit. In other words, accessible ...