#import "MainVC.h"
#import "Person.h"

@implementation MainVC
-(void)buttonAction
{
    [self.m_person setValue:@"yaohui" forKey:@"name"];
    [self.m_person setValue:[NSNumber numberWithInt:1] forKey:@"sexy"];
    [self.m_person setValue:@"sanguoyanyi" forKeyPath:@"book.bookname"];
}
-(void) initSubviews
{
    self.m_label = [[UILabel alloc] initWithFrame:CGRectMake(0, 64, 100, 40)];
    self.m_label.textColor = [UIColor redColor];
    self.m_label.text = [self.m_person valueForKey:@"name"];
    [self.view addSubview:_m_label];

    self.m_sexlabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 120, 100, 40)];
    self.m_sexlabel.textColor = [UIColor redColor];
    self.m_sexlabel.text = [NSString stringWithFormat:@"%@",[self.m_person valueForKey:@"sexy"]];
    [self.view addSubview:_m_sexlabel];

    self.m_booklabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 170, 100, 40)];
    self.m_booklabel.textColor = [UIColor redColor];
    self.m_booklabel.text = [self.m_person valueForKeyPath:@"book.bookname"];
    [self.view addSubview:_m_booklabel];
    
    
    UIButton * b = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    b.frame = CGRectMake(150, 64, 100, 30);
    b.backgroundColor = [UIColor grayColor];
    [b addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:b];
}
-(void)viewDidLoad
{
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    
    self.m_person = [[Person alloc] init];
    [self.m_person setValue:@"jinfangming" forKey:@"name"];
    [self.m_person setValue:[NSNumber numberWithInt:0] forKey:@"sexy"];

    Book* b = [Book new];
    self.m_person.book = b;
    
    [self.m_person setValue:@"hongloumeng" forKeyPath:@"book.bookname"];
    //[self.m_person setValue:newPerson forKey:@"person"];
    
    [self.m_person addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
    [self.m_person addObserver:self forKeyPath:@"sexy" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
    [self.m_person addObserver:self forKeyPath:@"book.bookname" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
    
    [self initSubviews];
}
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if([keyPath isEqualToString:@"name"])
    {
        self.m_label.text = [self.m_person valueForKey:@"name"];
    }else if([keyPath isEqualToString:@"sexy"])
    {
        self.m_sexlabel.text = [NSString stringWithFormat:@"%@",[self.m_person valueForKey:@"sexy"]];
    }else if([keyPath isEqualToString:@"book.bookname"])
    {
        self.m_booklabel.text = [self.m_person valueForKeyPath:@"book.bookname"];
    }
}
@end

解决 在observeValueForKeyPath:ofObject:change:context:方法里通过keyPath值来做调度，当Observe比较多的对象时，会使得代码变得杂乱和迷惑。 2. 必须手动的来注册和删除一个观察者，如果能自动做就好了。
归类observe
Observer.h

#import <Foundation/Foundation.h>

@interface Observer : NSObject

@property (nonatomic, weak) id target;
@property (nonatomic) SEL selector;
@property (nonatomic, weak) id observedObject;
@property (nonatomic, copy) NSString* keyPath;

+ (instancetype)observerWithObject:(id)object
                           keyPath:(NSString*)keyPath
                            target:(id)target
                          selector:(SEL)selector;
@end

Observe.m

#import "Observer.h"

@implementation Observer
+ (instancetype)observerWithObject:(id)object
                           keyPath:(NSString*)keyPath
                            target:(id)target
                          selector:(SEL)selector
{
    return [[Observer alloc] initWithObject:object keyPath:keyPath target:target selector:selector];
}
- (id)initWithObject:(id)object keyPath:(NSString*)keyPath target:(id)target selector:(SEL)selector
{
    if (self = [super init]) {
        self.target = target;
        self.selector = selector;
        self.observedObject = object;
        self.keyPath = keyPath;
        [object addObserver:self forKeyPath:keyPath options:0 context:NULL];
    }
    return self;
}

- (void)observeValueForKeyPath:(NSString*)keyPath ofObject:(id)object change:(NSDictionary*)change context:(void*)context
{
    id strongTarget = self.target;
    if ([strongTarget respondsToSelector:self.selector]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        [strongTarget performSelector:self.selector];
#pragma clang diagnostic pop
    }
}

@end

vc中观察设置

self.usernameObserver = [Observer observerWithObject:self.m_person
                                                 keyPath:@"name"
                                                  target:self
                                                selector:@selector(usernameChanged)];