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When to use enumerateObjectsUsingBlock vs. for
...
Ultimately, use whichever pattern you want to use and comes more naturally in the context.
While for(... in ...) is quite convenient and syntactically brief, enumerateObjectsUsingBlock: has a number of features that may or may not prove interesting:
enumerateObjectsUsingBlock: will be as fas...
通信连接组件 · App Inventor 2 中文网
...像的Base64编码及解码方法，便于图像文件的通信传输。此插件仅提供2个函数，使用非常方便，几乎没有学习成本。
属性
无
事件
无
方法
EncodeImage
DecodeImage
MqttClient 拓展
.aix 拓展及demo程序打包下载：
UrsAI2Paho.zip
MQT...
Skip certain tables with mysqldump
...table=schema.table2 > db-data.sql
The resulting two files are structurally sound but the dumped data is now ~500MB rather than 9GB, much better for me. I can now import these two files into another database for testing purposes without having to worry about manipulating 9GB of data or running o...
使用App Inventor扩展实现多点触控：Scale Detector · App Inventor 2 中文网
...etector.aix 扩展。
请记住，扩展机制仍然不稳定并且正在开发中。 随着系统的发展，你在步骤 (2) 和 (3) 中构建的任何 aia 文件可能需要重新构建。
内容
多点触控演示应用
实现ScaleDetector扩展
App Inventor 没有内置多点触控...
Alarm 闹钟扩展 · App Inventor 2 中文网
...小米设备上请求特殊权限。
工具
对于开发自己的扩展，我收集了一些提示：AI2 FAQ：开发扩展。
原文链接
原版英文文档：Ullis Roboter Seite - AI2 Alarm
您的改进建议 ...
Multi-statement Table Valued Function vs Inline Table Valued Function
...e compiler cannot use any table statistics on the tables in the MSTVF. So, all things being equal, (which they rarely are), the ITVF will perform better than the MSTVF. In my tests, the performance difference in completion time was negligible however from a statistics standpoint, it was noticeable.
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Queries vs. Filters
...erefore faster than queries. Have a look here too. Let's say a query is usually something that the users type and pretty much unpredictable, while filters help users narrowing down the search results , for example using facets.
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Python != operation vs “is not”
...right hand side and the left hand side are the very same object. No methodcalls are done, objects can't influence the is operation.
You use is (and is not) for singletons, like None, where you don't care about objects that might want to pretend to be None or where you want to protect against object...
String concatenation: concat() vs “+” operator
...then throwing it away when you create the final String. In practice memory allocation is surprisingly fast.
Update: As Pawel Adamski notes, performance has changed in more recent HotSpot. javac still produces exactly the same code, but the bytecode compiler cheats. Simple testing entirely fails bec...
'printf' vs. 'cout' in C++
...letely on operator overloading, so there is no issue with custom formats - all you do is define a subroutine taking std::ostream as the first argument and your type as second. As such, there are no namespace problems - as long you have a class (which isn't limited to one character), you can have wor...