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虚拟摇杆使用指导 · App Inventor 2 中文网
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方向数设为 4，先用蓝牙客户端连上小车（如 HC-05 模块），小车程序约定 F 前进、B 后退、L 左转、R 右转、S 停车：
各案例独立使用；组合到同一屏幕时，将同名事件的处理合并到一个事件积木中。
when 虚拟摇杆1.Direc...
COUNT DISTINCT with CONDITIONS
...count(distinct tag) as tag_count,
count(distinct (case when entryId > 0 then tag end)) as positive_tag_count
from
your_table_name;
The first count(distinct...) is easy.
The second one, looks somewhat complex, is actually the same as the first one, except that you use case...when clause. In ...
How do I draw a grid onto a plot in Python?
...lot using pylab in Python and now I would like to superimpose a grid of 10x10 onto the scatter plot. How do I do that?
5 ...
Maven project version inheritance - do I have to specify the parent version?
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EDIT: Since Maven 3.5.0 there is a nice solution for this using ${revision} placeholder. See FrVaBe's answer for details. For previous Maven versions see my original answer below.
No, there isn't. You always have to specify parent's version. Fo...
How to count total lines changed by a specific author in a Git repository?
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320
The output of the following command should be reasonably easy to send to script to add up the to...
C# short/long/int literal format?
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var d = 1.0d; // double
var d0 = 1.0; // double
var d1 = 1e+3; // double
var d2 = 1e-3; // double
var f = 1.0f; // float
var m = 1.0m; // decimal
var i = 1; // int
var ui = 1U; // uint
var ul = 1UL; // ulong
var l =...
SQL Server 2008 Windows Auth Login Error: The login is from an untrusted domain
When attempting to connect to a SQL Server 2008 Instance using Management Studio, I get the following error:
35 Answers
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Check that an email address is valid on iOS [duplicate]
...ng
{
BOOL stricterFilter = NO; // Discussion http://blog.logichigh.com/2010/09/02/validating-an-e-mail-address/
NSString *stricterFilterString = @"^[A-Z0-9a-z\\._%+-]+@([A-Za-z0-9-]+\\.)+[A-Za-z]{2,4}$";
NSString *laxString = @"^.+@([A-Za-z0-9-]+\\.)+[A-Za-z]{2}[A-Za-z]*$";
NSString *ema...
An “and” operator for an “if” statement in Bash
...US} is empty. It would probably be better to do:
if ! [ "${STATUS}" -eq 200 ] 2> /dev/null && [ "${STRING}" != "${VALUE}" ]; then
or
if [ "${STATUS}" != 200 ] && [ "${STRING}" != "${VALUE}" ]; then
It's hard to say, since you haven't shown us exactly what is going wrong wit...