传送门：How to draw a n sided regular polygon in cartesian coordinates?
先上公式，假设要画正N边型，外接圆的中心点坐标为（x_centre, y_centre)
x[n] = r * cos(2*pi*n/N + theta) + x_centre
y[n] = r * sin(2*pi*n/N + theta) + y_centre
这里如果theta取0，那么画出来是歪的。
想正的话，theta = pi[......]
转载自：《How To Present An Alert View Using UIAlertController When You Don't Have A View Controller》
Over the summer I updated a number of apps to iOS 9. A common tasks for me was replacing the deprecated UIAlertView with new UIAlertController class.[......]
有的时候，我们需要将iPhone投影到PC的屏幕上，这些可以通过AirPlay完成。
但是在PC上，需要一个AirPlay的Receiver，推荐一个免费好用的：
5K Player
https://www.5kplayer.com/[......]
Java APNS (com.notnoop.apns, v0.2.3) to send Push Notifications to my iOS app
传送门：《What's the correct format for Java APNS certificate?》
TLDR：