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AppInventor2项目是自动保存的吗？ - App Inventor 2 中文网 - 清泛IT社区，为创新赋能！
Q：AppInventor2项目是自动保存的吗？
先说结论：是的，自动保存。在界面或者代码块发生变化之后，会自动进行项目保存。
当然，如果要追求心里”踏实感“，建议可以手动再保存一次，项目菜单 -> 保存项目：
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UrsPahoMqttClient心跳问题解决——Paho底层已自动处理，设好KeepAlive就行...
问一下心跳PingReq报文怎么发的
目的为保持 MQTT 连接，否则会被踢下线。
用的是什么MQTT扩展？UrsPahoMqttClient。
结论：不需要手动发心跳，Paho底层已内置实现
UrsPahoMqttClient 封装的是 Eclipse Paho MQTT 客户端，心跳（PingReq）...
Can an Android NFC phone act as an NFC tag?
... a simple old nfc tag? Is there some application I'm not thinking of? Usually, you'd want to emulate something like a transit card, access key, or credit card which would require a secure element (I think, but not sure).
s...
How to destroy an object?
... objects as soon as the page is served. So this should only be needed on really long loops and/or heavy intensive pages.
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How to select from subquery using Laravel Query Builder?
...y there is no method to create subquery in FROM clause, so you need to manually use raw statement, then, if necessary, you will merge all the bindings:
$sub = Abc::where(..)->groupBy(..); // Eloquent Builder instance
$count = DB::table( DB::raw("({$sub->toSql()}) as sub") )
->mergeBin...
Convert String to Uri
... to its standards. For example, try to parse: http://www.google.com/search?q=cat|dog. An exception will be thrown for the vertical bar.
urllib makes it easy to convert a string to a java.net.URI. It will pre-process and escape the URL.
assertEquals("http://www.google.com/search?q=cat%7Cdog",
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What are some uses of decltype(auto)?
...code
For non-generic code, like the initial example you gave, you can manually select to get a reference as a return type:
auto const& Example(int const& i)
{
return i;
}
but in generic code you want to be able to perfectly forward a return type without knowing whether you are dea...
What is the difference between static_cast and C style casting?
...runtime.
Also, c++ style casts can be searched for easily, whereas it's really hard to search for c style casts.
Another big benefit is that the 4 different C++ style casts express the intent of the programmer more clearly.
When writing C++ I'd pretty much always use the C++ ones over the the C...
Insert a line at specific line number with sed or awk
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mac users: with homebrew, brew install gnu-sed and then use this with gsed
– cwd
Jan 10 '15 at 17:58
4
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Programmatically access currency exchange rates [closed]
... this, is there any information on what the parameters stand for? Specifically the "f" parameter. I can't find any info anywhere.
– Fishcake
Oct 8 '09 at 6:12
9
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