ios之断言更胜于NSLog
有时候我们需要不断的输出以用来调试程序,断言这个东西很少被人用到。今天看网上一大神写的代码
NSAssert(!gMenu, @"singleton object");
NSParameterAssert(view);
便查了下文档
#define NSParameterAssert(condition) NSAssert((condition), @"Invalid parameter not satisfying: %s", #condition)
#if !defined(_NSAssertBody) #define NSAssert(condition, desc, ...) do { __PRAGMA_PUSH_NO_EXTRA_ARG_WARNINGS if (!(condition)) { [[NSAssertionHandler currentHandler] handleFailureInMethod:_cmd object:self file:[NSString stringWithUTF8String:__FILE__] lineNumber:__LINE__ description:(desc), ##__VA_ARGS__]; } __PRAGMA_POP_NO_EXTRA_ARG_WARNINGS } while(0) #endif
本质还是NSAssert。
第一个参数为一个条件判断,如果为假,则抛出异常,显示第二个参数所描述的信息。
举个例子:
NSInteger a = 5; NSInteger b = 0; NSInteger c = 0; // 断言 NSAssert(b!=0, @"b 是 零");
只有在debug下,会导致crash,并在系统中显示:
2014-07-23 13:43:33.465 CatchCrash[8747:60b] *** Terminating app due to uncaught exception ‘NSInternalInconsistencyException‘, reason: ‘b 是 零‘ *** First throw call stack: ( 0 CoreFoundation 0x0000000101947495 __exceptionPreprocess + 165 1 libobjc.A.dylib 0x00000001016a699e objc_exception_throw + 43 2 CoreFoundation 0x000000010194731a +[NSException raise:format:arguments:] + 106 3 Foundation 0x0000000101242f19 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 189 4 CatchCrash 0x0000000100001850 -[ViewController viewDidLoad] + 1056 5 UIKit 0x000000010034959e -[UIViewController loadViewIfRequired] + 562 6 UIKit 0x0000000100349777 -[UIViewController view] + 29 7 UIKit 0x000000010028996b -[UIWindow addRootViewControllerViewIfPossible] + 58 8 UIKit 0x0000000100289c70 -[UIWindow _setHidden:forced:] + 282 9 UIKit 0x0000000111039d73 -[UIWindowAccessibility(SafeCategory) _orderFrontWithoutMakingKey] + 68 10 UIKit 0x0000000100292ffa -[UIWindow makeKeyAndVisible] + 51 11 UIKit 0x000000010024ec98 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1788 12 UIKit 0x0000000100252a0c -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 660 13 UIKit 0x0000000100263d4c -[UIApplication handleEvent:withNewEvent:] + 3189 14 UIKit 0x0000000100264216 -[UIApplication sendEvent:] + 79 15 UIKit 0x0000000100254086 _UIApplicationHandleEvent + 578 16 GraphicsServices 0x0000000103ac071a _PurpleEventCallback + 762 17 GraphicsServices 0x0000000103ac01e1 PurpleEventCallback + 35 18 CoreFoundation 0x00000001018c9679 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41 19 CoreFoundation 0x00000001018c944e __CFRunLoopDoSource1 + 478 20 CoreFoundation 0x00000001018f2903 __CFRunLoopRun + 1939 21 CoreFoundation 0x00000001018f1d83 CFRunLoopRunSpecific + 467 22 UIKit 0x00000001002522e1 -[UIApplication _run] + 609 23 UIKit 0x0000000100253e33 UIApplicationMain + 1010 24 CatchCrash 0x0000000100001c47 main + 103 25 libdyld.dylib 0x0000000101fdf5fd start + 1 26 ??? 0x0000000000000001 0x0 + 1 ) libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)
上面代码区第一行少了一些字符串,在下面重新写了下。就是写出了crash的原因
*** Terminating app due to uncaught exception ‘NSInternalInconsistencyException‘, reason: ‘b 是 零‘
*** First throw call stack:
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