问题
I really can't figure this out. When I click a link to open Safari from within my app, browse through the webpage, then return to my app, I can open and browse two tabBarItems in my UITabBar. But, when I try to select the one atIndex: 0, I get an EXEC_BAD_ACCESS and the following :(. Can anyone help me figure out how to make this not happen? I currently don't have any code that executes in will or didEnterBackground or Foreground. None. So the problem must be in the UIViewController for the first tab. (Oh and I don't know why it's adding a subview. Related?). Thoughts?
Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x0109ba63 objc_msgSend + 23
1 UIKit 0x0031f3df -[UIView(Internal) _didMoveFromWindow:toWindow:] + 966
2 UIKit 0x0031f1b0 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 407
3 UIKit 0x0031f1b0 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 407
4 UIKit 0x0031f1b0 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 407
5 UIKit 0x0031f1b0 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 407
6 UIKit 0x0031f1b0 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 407
7 UIKit 0x0031dfc4 -[UIView(Hierarchy) _postMovedFromSuperview:] + 166
8 UIKit 0x00316dfc -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1080
9 UIKit 0x0031514f -[UIView(Hierarchy) addSubview:] + 57
10 UIKit 0x003725ac -[UITransitionView transition:fromView:toView:] + 563
11 UIKit 0x00371955 -[UITransitionView transition:toView:] + 129
12 UIKit 0x003a6383 -[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:] + 459
13 UIKit 0x003a4d86 -[UITabBarController transitionFromViewController:toViewController:] + 64
14 UIKit 0x003a6b7e -[UITabBarController _setSelectedViewController:] + 263
15 UIKit 0x003a69ed -[UITabBarController _tabBarItemClicked:] + 352`
回答1:
The BAD_ACCESS means you are likely accessing something that points to memory that has been released. In the situation you describe, it's very possible that your views are unloading due to a low memory warning - particularly ones that aren't visible. If you aren't prepared for this unloading, when the view reloads, bad things usually happen. Make sure you are appropriately handling your viewDidUnload method and the reciprocal viewDidLoad in your view controllers.
来源：https://stackoverflow.com/questions/4870217/my-iphone-app-crashes-after-opening-it-from-background-and-selecting-tab-atindex