NSObject is the root class of most Objective-C class hierarchies. Through NSObject, objects inherit a basic interface to the runtime system and the ability to behave as Objective-C objects.
NSObject 是 Objective-C 的大多數(shù)類的根類，自身實現(xiàn)了 <NSObject> 協(xié)議。
頭文件申明為：
@interface NSObject <NSObject> {
Class isa OBJC_ISA_AVAILABILITY;
}
+ (void)load;
+ (void)initialize;
- (instancetype)init
#if NS_ENFORCE_NSOBJECT_DESIGNATED_INITIALIZER
NS_DESIGNATED_INITIALIZER
#endif
;
+ (instancetype)new OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)allocWithZone:(struct _NSZone *)zone OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)alloc OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
- (void)dealloc OBJC_SWIFT_UNAVAILABLE("use 'deinit' to define a de-initializer");
- (void)finalize;
- (id)copy;
- (id)mutableCopy;
+ (id)copyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
+ (id)mutableCopyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
+ (BOOL)instancesRespondToSelector:(SEL)aSelector;
+ (BOOL)conformsToProtocol:(Protocol *)protocol;
- (IMP)methodForSelector:(SEL)aSelector;
+ (IMP)instanceMethodForSelector:(SEL)aSelector;
- (void)doesNotRecognizeSelector:(SEL)aSelector;
- (id)forwardingTargetForSelector:(SEL)aSelector __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
- (void)forwardInvocation:(NSInvocation *)anInvocation OBJC_SWIFT_UNAVAILABLE("");
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector OBJC_SWIFT_UNAVAILABLE("");
+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector OBJC_SWIFT_UNAVAILABLE("");
- (BOOL)allowsWeakReference UNAVAILABLE_ATTRIBUTE;
- (BOOL)retainWeakReference UNAVAILABLE_ATTRIBUTE;
+ (BOOL)isSubclassOfClass:(Class)aClass;
+ (BOOL)resolveClassMethod:(SEL)sel __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
+ (BOOL)resolveInstanceMethod:(SEL)sel __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
+ (NSUInteger)hash;
+ (Class)superclass;
+ (Class)class OBJC_SWIFT_UNAVAILABLE("use 'aClass.self' instead");
+ (NSString *)description;
+ (NSString *)debugDescription;
@end
new / alloc / copy / mutableCopy 之類的是創(chuàng)建/拷貝方法。
instancesRespondToSelector / conformsToProtocol 之類的方法也比較簡單，判斷該類/該類的實例對象是否響應(yīng)某 Selector / Protocol 等。
forwardingTargetForSelector / forwardingInvocation / resolveClassMethod / resolveInstanceMethod 之類的方法是 NSObject 的消息轉(zhuǎn)發(fā)機制，如果某對象沒有實現(xiàn)某方法，就會進行消息轉(zhuǎn)發(fā)。內(nèi)容比較多，這里先不說。
<NSObject>協(xié)議申明為：
@protocol NSObject
- (BOOL)isEqual:(id)object;
@property (readonly) NSUInteger hash;
@property (readonly) Class superclass;
- (Class)class OBJC_SWIFT_UNAVAILABLE("use 'anObject.dynamicType' instead");
- (instancetype)self;
- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
- (BOOL)isProxy;
- (BOOL)isKindOfClass:(Class)aClass;
- (BOOL)isMemberOfClass:(Class)aClass;
- (BOOL)conformsToProtocol:(Protocol *)aProtocol;
- (BOOL)respondsToSelector:(SEL)aSelector;
- (instancetype)retain OBJC_ARC_UNAVAILABLE;
- (oneway void)release OBJC_ARC_UNAVAILABLE;
- (instancetype)autorelease OBJC_ARC_UNAVAILABLE;
- (NSUInteger)retainCount OBJC_ARC_UNAVAILABLE;
- (struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
@property (readonly, copy) NSString *description;
@optional
@property (readonly, copy) NSString *debugDescription;
@end
performSelector 由 另外一篇文章 從多線程的角度總結(jié)了點知識點，其他略過不表。
和 UIKit 相關(guān)的繼承自 NSObject的組織架構(gòu)圖：
常用到需要注意的關(guān)鍵點在于 UIResponder 和 UIControl 的特性。
- UIResponder
- (nullable UIResponder*)nextResponder;
- (BOOL)canBecomeFirstResponder; // default is NO
- (BOOL)becomeFirstResponder;
- (BOOL)canResignFirstResponder; // default is YES
- (BOOL)resignFirstResponder;
- (BOOL)isFirstResponder;
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesCancelled:(nullable NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEstimatedPropertiesUpdated:(NSSet * _Nonnull)touches NS_AVAILABLE_IOS(9_1);
這些是比較常用到的 Api，還有一些 pressesBegan:withEvent: / motionBegan:withEvent: 之類的同 touchesBegan:withEvent: 類似，只是手勢不同。
可以看出 UIResponder 的特點，它是為了處理交互事件的。所以能夠處理交互的類大都繼承自 UIResponder，包括 UIView，UIViewController，UIApplication。這里提一句，項目自動生成的 AppDelegate 類也是繼承自 UIResponder。
- UIControl
@property(nonatomic,getter=isEnabled) BOOL enabled;
@property(nonatomic,getter=isSelected) BOOL selected;
@property(nonatomic,getter=isHighlighted) BOOL highlighted;
@property(nonatomic,readonly) UIControlState state;
// add target/action for particular event. you can call this multiple times and you can specify multiple target/actions for a particular event.
// passing in nil as the target goes up the responder chain. The action may optionally include the sender and the event in that order
// the action cannot be NULL. Note that the target is not retained.
- (void)addTarget:(nullable id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents;
- (void)removeTarget:(nullable id)target action:(nullable SEL)action forControlEvents:(UIControlEvents)controlEvents;
- (NSSet *)allTargets;
- (UIControlEvents)allControlEvents;
- (nullable NSArray<NSString *> *)actionsForTarget:(nullable id)target forControlEvent:(UIControlEvents)controlEvent;
UIControl 的一個重要的特性就是擁有 enabled / selected / highlighted 之類的屬性，而且它還有個很重要的方法 addTarget:action:forControlEvents: 。很明顯的 目標(biāo) - 動作 模式。當(dāng)該目標(biāo)觸發(fā) **ControlEvents 時調(diào)用對應(yīng)的 action。
主要總結(jié)了下 UIResponder 和 UIControl 的比較明顯的特點。所有 UIView 的事件處理都是在 UIResponder 類中實現(xiàn)的，所有帶有交互處理的比如 UIButton，UISlider 都是繼承自 UIControl，實現(xiàn)了比較重要的 addTarget:action:forControlEvents: 方法。
