return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
这是我的堆栈跟踪：
2016-02-18 23:51:46.695 Lab3[9315:323419] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<ViewController 0x7fdb6053b5d0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key billAmountTextField.'
*** First throw call stack:
(
0 CoreFoundation 0x000000010f975e65 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010f3eedeb objc_exception_throw + 48
2 CoreFoundation 0x000000010f975aa9 -[NSException raise] + 9
3 Foundation 0x000000010efbb9bb -[NSObject(NSKeyValueCoding) setValue:forKey:] + 288
4 UIKit 0x000000010feb1320 -[UIViewController setValue:forKey:] + 88
5 UIKit 0x00000001100dff41 -[UIRuntimeOutletConnection connect] + 109
6 CoreFoundation 0x000000010f8b64a0 -[NSArray makeObjectsPerformSelector:] + 224
7 UIKit 0x00000001100de924 -[UINib instantiateWithOwner:options:] + 1864
8 UIKit 0x000000010feb7eea -[UIViewController _loadViewFromNibNamed:bundle:] + 381
9 UIKit 0x000000010feb8816 -[UIViewController loadView] + 178
10 UIKit 0x000000010feb8b74 -[UIViewController loadViewIfRequired] + 138
11 UIKit 0x000000010feb92e7 -[UIViewController view] + 27
12 UIKit 0x000000010fd8fab0 -[UIWindow addRootViewControllerViewIfPossible] + 61
13 UIKit 0x000000010fd90199 -[UIWindow _setHidden:forced:] + 282
14 UIKit 0x000000010fda1c2e -[UIWindow makeKeyAndVisible] + 42
15 UIKit 0x000000010fd1a663 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 4131
16 UIKit 0x000000010fd20cc6 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1760
17 UIKit 0x000000010fd1de7b -[UIApplication workspaceDidEndTransaction:] + 188
18 FrontBoardServices 0x00000001126ee754 -[FBSSerialQueue _performNext] + 192
19 FrontBoardServices 0x00000001126eeac2 -[FBSSerialQueue _performNextFromRunLoopSource] + 45
20 CoreFoundation 0x000000010f8a1a31 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
21 CoreFoundation 0x000000010f89795c __CFRunLoopDoSources0 + 556
22 CoreFoundation 0x000000010f896e13 __CFRunLoopRun + 867
23 CoreFoundation 0x000000010f896828 CFRunLoopRunSpecific + 488
24 UIKit 0x000000010fd1d7cd -[UIApplication _run] + 402
25 UIKit 0x000000010fd22610 UIApplicationMain + 171
26 Lab3 0x000000010eeec1bf main + 111
27 libdyld.dylib 0x00000001120b192d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)