@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(shí)創(chuàng)建calendar對(duì)象的強(qiáng)指針，而self.calendar是弱指針，當(dāng)view不釋放，也會(huì)指向calendar，當(dāng)view釋放，則self。calendar也不再持有該對(duì)象。
所以self.calendar=[[FSCalendar alloc] initWithFrame:CGRectMake(0, 44, 320, 300)];是錯(cuò)誤的寫法，因?yàn)樵搶?duì)象創(chuàng)建后立即被釋放。