iOS 编写高质量Objective-C代码（二）

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@property (nonatomic, strong) UIView *qiShareView; 

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@synthesize qiShareView = _qiShareView;
- (UIView *)qiShareView;
- (void)setQiShareView:(UIView *)qiShareView; 

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@dynamic qiShareView; 

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@property (nonatomic, getter=isOn) BOOL on; 

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- (instancetype)initWithDic:(NSDictionary *)dic {self = [super init];if (self) {_qi = dic[@"qi"];_share = dic[@"share"];}return self;
} 

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- (UIView *)qiShareView {if (!_qiShareView) {_qiShareView = [UIView new];}return _qiShareView;
} 

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NSString *aString = @"iPhone 8";
NSString *bString = [NSString stringWithFormat:@"iPhone %i", 8];
NSLog(@"%d", [aString isEqual:bString]);
NSLog(@"%d", [aString isEqualToString:bString]);
NSLog(@"%d", aString == bString); 

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id maybeAnArray = @[];
if ([maybeAnArray class] == [NSArray class]) { //Code will never be executed
} 

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id maybeAnArray = @[];
if ([maybeAnArray isKindOfClass [NSArray class]) {// Code probably be executed
} 

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#import <objc/runtime.h> 

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/** 
 * Sets an associated value for a given object using a given key and association policy.
 * 
 * @param object The source object for the association.
 * @param key The key for the association.
 * @param value The value to associate with the key key for object. Pass nil to clear an existing association.
 * @param policy The policy for the association. For possible values, see “Associative Object Behaviors.”
 */
OBJC_EXPORT void
objc_setAssociatedObject(id _Nonnull object, const void * _Nonnull key, id _Nullable value, objc_AssociationPolicy policy) 

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/** 
 * Returns the value associated with a given object for a given key.
 * 
 * @param object The source object for the association.
 * @param key The key for the association.
 * 
 * @return The value associated with the key e key for e object.
 */
OBJC_EXPORT id _Nullable
objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key) 

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/** 
 * Removes all associations for a given object.
 * 
 * @param object An object that maintains associated objects.
 * 
 * @note The main purpose of this function is to make it easy to return an object 
 *to a "pristine state”. You should not use this function for general removal of
 *associations from objects, since it also removes associations that other clients
 *may have added to the object. Typically you should use c objc_setAssociatedObject 
 *with a nil value to clear an association.
 * 
 */
OBJC_EXPORT void
objc_removeAssociatedObjects(id _Nonnull object) 

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void objc_msgSend(id self, SEL cmd, ...) 

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id return = [git commit:parameter]; 

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id return = objc_msgSend(git, @selector(commit), parameter); 

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/** 
 * Returns a specified instance method for a given class.
 * 
 * @param cls The class you want to inspect.
 * @param name The selector of the method you want to retrieve.
 * 
 * @return The method that corresponds to the implementation of the selector specified by 
 *e name for the class specified by e cls, or c NULL if the specified class or its 
 *superclasses do not contain an instance method with the specified selector.
 *
 * @note This function searches superclasses for implementations, whereas c class_copyMethodList does not.
 */
OBJC_EXPORT Method _Nullable
class_getInstanceMethod(Class _Nullable cls, SEL _Nonnull name) 

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/** 
 * Exchanges the implementations of two methods.
 * 
 * @param m1 Method to exchange with second method.
 * @param m2 Method to exchange with first method.
 * 
 * @note This is an atomic version of the following:
 *code 
 *IMP imp1 = method_getImplementation(m1);
 *IMP imp2 = method_getImplementation(m2);
 *method_setImplementation(m1, imp2);
 *method_setImplementation(m2, imp1);
 *endcode
 */
OBJC_EXPORT void
method_exchangeImplementations(Method _Nonnull m1, Method _Nonnull m2) 

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Method method1 = class_getInstanceMethod(self, @selector(method1:));
Method method2 = class_getInstanceMethod(self, @selector(method2:));
method_exchangeImplementations(method1, method2); 

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typedef struct objc_class *Class; 

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struct objc_class {Class _Nonnull isaOBJC_ISA_AVAILABILITY;//!< 指向metaClass(元类)的指针

#if !__OBJC2__Class _Nullable super_classOBJC2_UNAVAILABLE;//!< 父类const char * _Nonnull name OBJC2_UNAVAILABLE;//!< 类名long version OBJC2_UNAVAILABLE;//!< 类的版本信息，默认为0long infoOBJC2_UNAVAILABLE;//!< 类信息，供运行期使用的一些位标识long instance_size OBJC2_UNAVAILABLE;//!< 该类的实例变量大小struct objc_ivar_list * _Nullable ivarsOBJC2_UNAVAILABLE;//!< 该类的成员变量链表struct objc_method_list * _Nullable * _Nullable methodListsOBJC2_UNAVAILABLE;//!< 方法定义的链表struct objc_cache * _Nonnull cache OBJC2_UNAVAILABLE;//!< 方法缓存表struct objc_protocol_list * _Nullable protocolsOBJC2_UNAVAILABLE;//!< 协议链表
#endif

} OBJC2_UNAVAILABLE;
/* Use `Class` instead of `struct objc_class *` */