何时在uiviewController上拨打DealLoc，当它被弹出时？
说如果我有这样的导航堆栈： uinavigationController-＆gt; viewController1-＆gt; viewController2 。当ViewController2弹出时，系统是否保证了下面方法的执行顺序？
- dealloc viewController2
- viewwillappear viewController1
我已经测试了一段时间，只看到 dreamloc 首先称为 dreamloc 可以保证，即，在ViewController2的 dealloc 之前，是否也可以调用ViewController1的ViewController1的 ViewWillAppear ？
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There is no such guarantee of order, and it's even likely
viewWillAppearof your ViewController1 is called beforeViewController2.deallocis called.原因是，根据自动发行池和内部参考，系统可能仍然对视图控制器进行引用，该视图控制器刚刚消失/当它调用视图控制器的 < em>大约要显示。
viewwillappear如果在弹出viewController2时需要清理以进行清理，请实现
viewwilldisappear/viewDidDisappear。同样，不能保证vc2.viewwilldisappear将在vc1.viewwillappear之前被调用vc1.viewdidappear（注意 did ，而不是最后一个中的）。There is no such guarantee of order, and it's even likely
viewWillAppearof your ViewController1 is called beforeViewController2.deallocis called.The reason is that depending on autorelease pools and internal references, it's likely the system still has a reference to the view controller that is just disappearing/has just disappeared when it calls the
viewWillAppearof the view controller that's about to get shown.If you require cleanup to be run when ViewController2 is popped, implement
viewWillDisappear/viewDidDisappear. Again, there is no guarantee thatvc2.viewWillDisappearwill be called beforevc1.viewWillAppear, but you can rely onvc2.viewWillDisappeargetting called beforevc1.viewDidAppear(noteDid, notWillin the last one).