為什么在設置UIWindow的rootViewController屬性時，viewDidLoad被調用了兩次？

Question

已經有幾個類似的問題，但它與我的情況並不完全相同。 只需啟動一個新的基於視圖的項目，使用NSLog語句添加viewDidLoad和awakeFromNib ，並在MainWindow.xib進行以下更改：

• 刪除應用程序委托中的視圖控制器連接。
• 將UIWindow's rootViewController委托連接到App View Controller實例。

第一次調用的堆棧跟蹤：

#0     0x000025c0 in -[foozaViewController viewDidLoad] at /Users/rafael/Downloads/fooza/fooza/foozaViewController.m:38
#1     0x000cd089 in -[UIViewController view] ()
#2     0x00040d42 in -[UIWindow addRootViewControllerViewIfPossible] ()
#3     0x0079d5e5 in -[NSObject(NSKeyValueCoding) setValue:forKey:] ()
#4     0x00050ff6 in -[UIView(CALayerDelegate) setValue:forKey:] ()
#5     0x0021930c in -[UIRuntimeOutletConnection connect] ()
#6     0x00d418cf in -[NSArray makeObjectsPerformSelector:] ()
#7     0x00217d23 in -[UINib instantiateWithOwner:options:] ()
#8     0x00219ab7 in -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:] ()
#9     0x0001f17a in -[UIApplication _loadMainNibFile] ()
#10     0x0001fcf4 in -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] ()
#11     0x0002a617 in -[UIApplication handleEvent:withNewEvent:] ()
#12     0x00022abf in -[UIApplication sendEvent:] ()
#13     0x00027f2e in _UIApplicationHandleEvent ()
#14     0x01004992 in PurpleEventCallback ()
#15     0x00dac944 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#16     0x00d0ccf7 in __CFRunLoopDoSource1 ()
#17     0x00d09f83 in __CFRunLoopRun ()
#18     0x00d09840 in CFRunLoopRunSpecific ()
#19     0x00d09761 in CFRunLoopRunInMode ()
#20     0x0001f7d2 in -[UIApplication _run] ()
#21     0x0002bc93 in UIApplicationMain ()
#22     0x000020d9 in main ()

這是來自第二個電話的追蹤：

#0     0x000025c0 in -[foozaViewController viewDidLoad] at /Users/rafael/Downloads/fooza/fooza/foozaViewController.m:38
#1     0x00002555 in -[foozaViewController awakeFromNib] ()
#2     0x00217f26 in -[UINib instantiateWithOwner:options:] ()
#3     0x00219ab7 in -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:] ()
#4     0x0001f17a in -[UIApplication _loadMainNibFile] ()
#5     0x0001fcf4 in -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] ()
#6     0x0002a617 in -[UIApplication handleEvent:withNewEvent:] ()
#7     0x00022abf in -[UIApplication sendEvent:] ()
#8     0x00027f2e in _UIApplicationHandleEvent ()
#9     0x01004992 in PurpleEventCallback ()
#10     0x00dac944 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#11     0x00d0ccf7 in __CFRunLoopDoSource1 ()
#12     0x00d09f83 in __CFRunLoopRun ()
#13     0x00d09840 in CFRunLoopRunSpecific ()
#14     0x00d09761 in CFRunLoopRunInMode ()
#15     0x0001f7d2 in -[UIApplication _run] ()
#16     0x0002bc93 in UIApplicationMain ()
#17     0x000020d9 in main ()

這是期望的行為還是錯誤？ 我們是否仍然應該使用更傳統的方式將出口連接到應用程序委托中的根視圖控制器以維持理智的viewDidLoad / viewDidUnload比率，或者我們應該忽略Apple的規則並且不要在awakeFromNib調用super並使用UIWindow的新的rootViewController屬性？

Answer 1

它看起來像一個bug，因為它只能在Xcode 4中重現。我會提交一個bug。

另請參見http://shurl.at/5u(Apple Developer論壇）