深入理解block的收藏

http://www.cocoachina.com/cms/wap.php?action=article&id=17936

http://www.cnblogs.com/yajunLi/p/6203222.html?utm_source=itdadao&utm_medium=referral

原文地址:https://www.cnblogs.com/rendaochoucheng/p/7154649.html