IOS proactively throws exceptions

Question:

What's the best way to throw an exception in objective-c/cocoa?

Answer:

Use [NSException raise:format:] as follows:

[NSException raise:@"Invalid foo value" format:@"foo of %d is invalid", foo];

此时控制台会Log：

*** Terminating app due to uncaught exception 'Invalid foo value', reason: 'foo of 9999 is invalid'
*** First throw call stack:
(
	0   CoreFoundation                      0x0083dca6 __exceptionPreprocess + 182
	1   libobjc.A.dylib                     0x004e18bf objc_exception_throw + 44
	2   CoreFoundation                      0x0083dbcd +[NSException raise:format:] + 141
	3   Exception                           0x0000e9fb -[ViewController viewDidLoad] + 139
	4   UIKit                               0x00d3f2f4 -[UIViewController loadViewIfRequired] + 771
	5   UIKit                               0x00d3f5e5 -[UIViewController view] + 35
	6   UIKit                               0x00c3a009 -[UIWindow addRootViewControllerViewIfPossible] + 66
	7   UIKit                               0x00c3a47b -[UIWindow _setHidden:forced:] + 314
	8   UIKit                               0x00c3a6f8 -[UIWindow _orderFrontWithoutMakingKey] + 49
	9   UIKit                               0x00c4931e -[UIWindow makeKeyAndVisible] + 80
	10  UIKit                               0x00be6e18 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 3159
	11  UIKit                               0x00be9efb -[UIApplication _runWithMainScene:transitionContext:completion:] + 1507
	12  UIKit                               0x00c02742 __84-[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:]_block_invoke + 59
	13  UIKit                               0x00be8c3e -[UIApplication workspaceDidEndTransaction:] + 29
	14  FrontBoardServices                  0x030bcbce __37-[FBSWorkspace clientEndTransaction:]_block_invoke_2 + 43
	15  FrontBoardServices                  0x030bc834 __40-[FBSWorkspace _performDelegateCallOut:]_block_invoke + 54
	16  FrontBoardServices                  0x030ce455 __31-[FBSSerialQueue performAsync:]_block_invoke + 26
	17  CoreFoundation                      0x00762540 __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 16
	18  CoreFoundation                      0x007577d3 __CFRunLoopDoBlocks + 195
	19  CoreFoundation                      0x00756f38 __CFRunLoopRun + 936
	20  CoreFoundation                      0x007568cb CFRunLoopRunSpecific + 443
	21  CoreFoundation                      0x007566fb CFRunLoopRunInMode + 123
	22  UIKit                               0x00be8555 -[UIApplication _run] + 571
	23  UIKit                               0x00bebba5 UIApplicationMain + 1526
	24  Exception                           0x0000eddd main + 141
	25  libdyld.dylib                       0x02af1ac9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

But in fact, Apple does not recommend that we throw an exception, which consumes too much resources.

Reference:

http://stackoverflow.com/questions/324284/throwing-an-exception-in-objective-c-cocoa