完整代碼：Demo-iOS

//
//  ViewController.m
//  Runtime
//
//  Created by Yuhui Huang on 12/1/16.
//  Copyright ? 2016 Yuhui Huang. All rights reserved.
//

#import "ViewController.h"
#import <objc/runtime.h>

///-----------------------------------------------------------------------------
/// http://nshipster.com/associated-objects
///-----------------------------------------------------------------------------
#pragma mark - Associated Objects -

/**
 Associated Objects—or Associative References, as they were originally known—are a feature of the Objective-C 2.0 runtime, introduced in OS X Snow Leopard (available in iOS 4). The term refers to the following three C functions declared in <objc/runtime.h>, which allow objects to associate arbitrary values for keys at runtime:
 
 objc_setAssociatedObject
 objc_getAssociatedObject
 objc_removeAssociatedObjects
 Why is this useful? It allows developers to add custom properties to existing classes in categories, which is an otherwise notable shortcoming for Objective-C.
 
 http://nshipster.com/associated-objects
 */
@interface NSObject (AssociatedObject)
@property (nonatomic, strong) id associatedObject;
@end


@implementation NSObject (AssociatedObject)
@dynamic associatedObject;

/**
 It is often recommended that they key be a static char—or better yet, the
 pointer to one. Basically, an arbitrary value that is guaranteed to be constant,
 unique, and scoped for use within getters and setters:
 
 static char kAssociatedObjectKey;
 
 objc_getAssociatedObject(self, &kAssociatedObjectKey);
 
 http://nshipster.com/associated-objects
 */
- (void)setAssociatedObject:(id)object {
    objc_setAssociatedObject(self, @selector(associatedObject), object, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (id)associatedObject {
    return objc_getAssociatedObject(self, @selector(associatedObject));
}

@end

///-----------------------------------------------------------------------------
/// http://tech.glowing.com/cn/method-swizzling-aop
///-----------------------------------------------------------------------------
#pragma mark - Method Swizzling 和 AOP 實(shí)踐 -
@interface UIViewController (MethodSwizzling)

@end


@implementation UIViewController (MethodSwizzling)

/**
 一般情況下，類(lèi)別里的方法會(huì)重寫(xiě)掉主類(lèi)里相同命名的方法畅形。如果有兩個(gè)類(lèi)別實(shí)現(xiàn)了相同命名的方法收夸，只有一個(gè)
 方法會(huì)被調(diào)用霹购。但 +load: 是個(gè)特例，當(dāng)一個(gè)類(lèi)被讀到內(nèi)存的時(shí)候， runtime 會(huì)給這個(gè)類(lèi)及它的每一個(gè)類(lèi)
 別都發(fā)送一個(gè) +load: 消息橱鹏。
 
 http://tech.glowing.com/cn/method-swizzling-aop
 */
+ (void)load
{
    swizzleMethod([self class], @selector(viewDidAppear:), @selector(swizzled_viewDidAppear:));
}

/**
 代碼看起來(lái)可能有點(diǎn)奇怪，像遞歸不是么堪藐。當(dāng)然不會(huì)是遞歸莉兰，因?yàn)樵?runtime 的時(shí)候，函數(shù)實(shí)現(xiàn)已經(jīng)被交換
 了礁竞。調(diào)用 viewDidAppear: 會(huì)調(diào)用你實(shí)現(xiàn)的 swizzled_viewDidAppear:糖荒，而在 swizzled_viewDidAppear: 里
 調(diào)用 swizzled_viewDidAppear: 實(shí)際上調(diào)用的是原來(lái)的 viewDidAppear:
 
 http://tech.glowing.com/cn/method-swizzling-aop
 */
- (void)swizzled_viewDidAppear:(BOOL)animated
{
    NSLog(@"---- swizzled_viewDidAppear 位置1 ----");
    
    // call original implementation
    [self swizzled_viewDidAppear:animated];
    
    NSLog(@"---- swizzled_viewDidAppear 位置2 ----");
}

/**
 要先嘗試添加原 selector 是為了做一層保護(hù)，因?yàn)槿绻@個(gè)類(lèi)沒(méi)有實(shí)現(xiàn) originalSelector 模捂，但其父
 類(lèi)實(shí)現(xiàn)了捶朵，那 class_getInstanceMethod 會(huì)返回父類(lèi)的方法。這樣 method_exchangeImplementations 替
 換的是父類(lèi)的那個(gè)方法狂男，這當(dāng)然不是你想要的综看。所以我們先嘗試添加 orginalSelector ，如果已經(jīng)存在并淋，再
 用 method_exchangeImplementations 把原方法的實(shí)現(xiàn)跟新的方法實(shí)現(xiàn)給交換掉寓搬。
 
 http://tech.glowing.com/cn/method-swizzling-aop
 */
void swizzleMethod(Class class, SEL originalSelector, SEL swizzledSelector)
{
    // the method might not exist in the class, but in its superclass
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    
    // class_addMethod will fail if original method already exists
    BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    
    // the method doesn’t exist and we just added one
    if (didAddMethod) {
        class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    }
    else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}


/**
 其實(shí)，這里還可以更簡(jiǎn)化點(diǎn)：直接用新的 IMP 取代原 IMP 县耽，而不是替換句喷。只需要有全局的函數(shù)指針指向
 原 IMP 就可以。
 http://tech.glowing.com/cn/method-swizzling-aop
 */
//void (gOriginalViewDidAppear)(id, SEL, BOOL);
//
//void newViewDidAppear(UIViewController *self, SEL _cmd, BOOL animated)
//{
//    // call original implementation
//    gOriginalViewDidAppear(self, _cmd, animated);
//
//    // Logging
//    [Logging logWithEventName:NSStringFromClass([self class])];
//}
//
//+ (void)load
//{
//    Method originalMethod = class_getInstanceMethod(self, @selector(viewDidAppear:));
//    gOriginalViewDidAppear = (void *)method_getImplementation(originalMethod);
//
//    if(!class_addMethod(self, @selector(viewDidAppear:), (IMP) newViewDidAppear, method_getTypeEncoding(originalMethod))) {
//        method_setImplementation(originalMethod, (IMP) newViewDidAppear);
//    }
//}

@end

///-----------------------------------------------------------------------------
/// http://tech.glowing.com/cn/implement-kvo
///-----------------------------------------------------------------------------
#pragma mark - 如何自己動(dòng)手實(shí)現(xiàn) KVO -

/**
 打印一個(gè)類(lèi)的全部方法
 http://tech.glowing.com/cn/implement-kvo
 */
static NSArray *ClassMethodNames(Class c)
{
    NSMutableArray *array = [NSMutableArray array];
    
    unsigned int methodCount = 0;
    Method *methodList = class_copyMethodList(c, &methodCount);
    unsigned int i;
    for(i = 0; i < methodCount; i++) {
        [array addObject: NSStringFromSelector(method_getName(methodList[i]))];
    }
    free(methodList);
    
    return array;
}


@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    
    [super viewDidLoad];
    
//    self.associatedObject = @"Hello, AssociatedObject!";
//    NSLog(@"%@", self.associatedObject);
    
//    NSArray *array = ClassMethodNames([UIViewController class]);
//    for (NSString *method in array) {
//        NSLog(@"----%@", method);
//    }
    
    if ([self hasSelector:@selector(viewDidLoad)]) {
        NSLog(@"true");
    } else {
        NSLog(@"false");
    }
}

- (void)viewDidAppear:(BOOL)animated {
    
    NSLog(@"---- viewDidAppear 位置1 ----");
    
    // 父類(lèi)的方法被替換了
    [super viewDidAppear:animated];
    
    NSLog(@"---- viewDidAppear 位置1 ----");
}

///-----------------------------------------------------------------------------
/// http://tech.glowing.com/cn/implement-kvo
///-----------------------------------------------------------------------------
#pragma mark - 如何自己動(dòng)手實(shí)現(xiàn) KVO -

/**
 判斷一個(gè)類(lèi)是否實(shí)現(xiàn)了某個(gè)方法
 http://tech.glowing.com/cn/implement-kvo
 */
- (BOOL)hasSelector:(SEL)selector
{
    Class clazz = object_getClass(self);
    unsigned int methodCount = 0;
    Method* methodList = class_copyMethodList(clazz, &methodCount);
    for (unsigned int i = 0; i < methodCount; i++) {
        SEL thisSelector = method_getName(methodList[i]);
        if (thisSelector == selector) {
            free(methodList);
            return YES;
        }
    }
    
    free(methodList);
    return NO;
}

@end