导致VC不能释放的几个原因

  1. delegate的属性不是weak
  2. NSTimer没有invalidate
  3. block中的强引用

  4. 调用了performSelector，退出时没有cancelPerformSelectorsWithTarget

    This method sets up a timer to perform the aSelector message on the current thread’s run loop. The timer is configured to run in the default mode (NSDefaultRunLoopMode).

    performSelector其实就是定时器，会强引用object。如果delay很长的话，就会被导致object很长时间不会被释放。