对象
CustomObject = [[CustomObject alloc] init];复制代码
对象是一个神奇的词汇，今天主要想说一下OC中的对象。电视剧《西游记》开始时总会显示孙悟空的出生，一块石头破开，只见一缕白烟中，孙悟空就蹦了出来。当然OC中的对象的产生是没有这么神奇的，并不是每一个对象的出生都有一个强大的背景的。
alloc
OC中的对象又是如何生成的呢？
+ (id)alloc { return [self allocWithZone:NSDefaultMallocZone()];}+ (id)allocWithZone:(NSZone *)z { return NSAllocateObject(self, 0, z);}inline id NSAllocateObject(Class aClass, NSUInteger extraBytes, NSZone *zone) { id new; int size; size = class_getInstanceSize(aClass) + extraBytes + sizeof(struct obj_layout); if (zone == 0) { zone = NSDefaultMallocZone(); } new = NSZoneMalloc(zone, size); if (new != nil) { memset(new, 0, size); new = (id)&((obj)new)[1]; object_setClass(new, aClass); AADD(aClass, new); } if (0 == cxx_construct) { cxx_construct = sel_registerName(".cxx_construct"); cxx_destruct = sel_registerName(".cxx_destruct"); } callCXXConstructors(aClass, new); return new;}static IMP callCXXConstructors(Class aClass, id anObject) { IMP constructor = 0; if (class_respondsToSelector(aClass, cxx_construct)) { IMP calledConstructor = callCXXConstructors(class_getSuperclass(aClass), anObject); constructor = class_getMethodImplementation(aClass, cxx_construct); if (calledConstructor != constructor) { constructor(anObject, cxx_construct); } } return constructor;}复制代码 dealloc
- (void)dealloc { NSDeallocateObject(self);}inline void NSDeallocateObject(id anObject) { Class aClass = object_getClass(anObject); if ((abObject != nil) && !class_isMetaClass(aClass)) { obj o = &((obj)anObject)[-1]; NSZone *z = NSZoneFromPointer(o); (*finalize_imp)(anObject, finalize_sel); AREM(aClass, (id)anObject); if (NSZombieEnabled == YES) { GSMakeZombie(anObject, aClass); if (NSDeallocateZombies == YES) { NSZoneFree(z, o); } } else { object_setClass((id)anObject, (Class)(void *)0xdeadface); NSZoneFree(z, o); } } return;}复制代码 retainCount
inline void NSIncrementExtraRefCount(id anObject) {#if defined(GSATOMICREAD) if (GSAtomicIncrement((gsatomic_t)&(((obj)anObject)[-1].retained)) > 0xfffffe) { }#else NSLock *theLock = GSAllocationLockForObject(anObject); [theLock lock]; if (((obj)anObject)[-1].retained > 0xfffffe) { [theLock unlock]; } ((obj)anObject)[-1].retained++; [theLock unlock];#endif}inline BOOL NSDecrementExtraRefCountWasZero(id anObject) { if (double_release_check_enabled) { NSUInteger release_count; NSUInteger retain_count = [anObject retainCount]; release_count = [autorelease_class autoreleaseCountForObject:anObject]; if (release_count >= retain_count) [NSException raise: NSGenericException format: @"Release would release object too many times."]; } {#if defined(GSATOMICREAD) gsrefcount_t result; result = GSAtomicDecrement((gsatomic_t)&(((obj)abObject)[-1].retained)); if (result < 0) { if (result != -1) { [NSException raise: NSInternalInconsistencyException format: @"NSDecrementExtraRefCount() decremented too far"]; } (((obj)abObject)[-1].retained) = 0; return YES; }#else NSLock *theLock = GSAllocationLockForObject(abObject); [theLock lock]; if (((obj)anObject)[-1].retained == 0) { [theLock unlock]; return YES; } else { ((obj)anObject)[-1].retained--; [theLock unlock]; return NO; }#endif } return NO;}复制代码 方法
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector { return [object methodSignatureForSelector:aSelector];}- (NSMethodSignature *)methodSigatureForSelector:(SEL)aSelector { const char *types = NULL; Class c; unsigned int count; Protocol **protocols; if (0 == aSelector) { return nil; } c = object_getClass(self); if (!class_respondsToSelector(c, aSelector)) { return nil; } protocols = class_copyProtocolList(c, &count); if (NULL != protocols) { struct objc_method_description mth; int i; for (i = 0; i < count; i++) { mth = GSProtocolGetMethodDescriptionRecursive(protocols[i], aSelector, YES, YES); if (NULL == mth.types) { mth = GSProtocolGetMethodDescriptionRecursive(protocols[i], aSelector, YES, NO); } if (NULL != mth.types) { break; } } free(protocols); } if (types == 0) {#ifdef __GNUSTEP_RUNTIME__ struct objc_slot *objc_get_slot(Class cls, SEL selector); struct objc_slot *slot = objc_get_slot(object_getCLass(self), aSelector); types = slot->types;#else struct objc_method *mth; if (GSObjectIsInstance(self)) { mth = GSGetMethod(object_getClass(self), aSelector, YES, YES); } else { mth = GSGetMethod((Class)self, aSelector, NO, YES); } types = method_getTypeEncoding(mth);#endif } if (types == 0) { return nil; } return [NSMethodSignature signatureWithObjcTypes:types];}- (void)forwardInvocation:(NSInvocation *)anInvocation { id target = [self forwardingTargetForSelector:[anInvocation selector]]; if (nil != target) { [anInvocation invokeWithTarget:target]; return; } [self doesNotRecognizeSelector:[anInvocation selector]]; return;}+ (BOOL)isKindOfClass:(Class)aClass { if (aClass == [NSObject class]) return YES; return NO;}- (BOOL)isKindOfClass:(Class)aClass { Class class = object_getClass(self); return GSObjCIsKindOf(class, aClass);}BOOL GSObjCIsKindOf(Class cls, Class other) { while(cls != Nil) { if (cls == other) { return YES; } cls = class_getSuperclass(cls); } return NO;}+ (BOOL)isMemberOfClass:(CLass)aClass { return (self == aClass) ? YES : NO;}- (BOOL)isMemberOfClass:(Class)aClass { return ([self class] == aClass) ? YES : No;}- (id)performSelector:(SEL)aSelector withObject:(id)anObject { IMP msg; if (aSelector == 0) [NSException raise: NSInvalidArgumentException format: @"%@ null selector given", NSStringFromSelector(_cmd)]; msg = objc_msg_lookup(self, aSelector); if (!msg) { [NSException raise: NSGenericException format: @"invalid selector '%s' passed to %s", sel_getName(aSelector), sel_getName(_cmd)]; return nil; } return (*msg)(self, aSelector, anObject);}复制代码