@property (weak , nonatomic) FSCalendar *calendar;
FSCalendar *calendar = [[FSCalendar alloc] initWithFrame:CGRectMake(0, 44, 320, 300)];
calendar.dataSource = self;
calendar.delegate = self;
[self.view addSubview:calendar];
self.calendar = calendar;
[self preferredStatusBarStyle];
理解：view是指向臨時創(chuàng)建calendar對象的強指針，而self.calendar是弱指針，當view不釋放河质，也會指向calendar眷篇，當view釋放抹缕，則self揣非。calendar也不再持有該對象叛氨。
所以self.calendar=[[FSCalendar alloc] initWithFrame:CGRectMake(0, 44, 320, 300)];是錯誤的寫法堕仔，因為該對象創(chuàng)建后立即被釋放擂橘。
