一、循环引用
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti
target:(id)aTarget
selector:(SEL)aSelector
userInfo:(nullable id)userInfo
repeats:(BOOL)yesOrNo;
1）NSTimer会持有target对象
二、runloop
原文：https://www.cnblogs.com/yangwenhuan/p/9010856.html