__weak typeof(self) weakSelf = self;myObj.myBlock = ^{ __strong typeof(self) strongSelf = weakSelf; if (strongSelf) { [strongSelf doSomething]; // strongSelf != nil // preemption, strongSelf still not nil [strongSelf doSomethingElse]; // strongSelf != nil } else { // Probably nothing... return; }};原文：http://www.cnblogs.com/rollrock/p/4878957.html