以实例讲解Objective-C中的KVO与KVC机制

-(void)viewDidLoad{ 
 
    // KVO,作为一个观察者,只要属性"contentSize"发生变化,回调方法里面就会通知 
    [_webView.scrollView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:NULL]; 
} 
 
//  回调方法 
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(voidvoid *)context 
{ 
    if(object == _webView.scrollView && [keyPath isEqualToString:@"contentSize"]) 
    { 
        //  得到最大的Y坐标 
        CGSize size = _webView.scrollView.contentSize; 
       
        if (size.height > 568.0) { 
             
            // 遮挡广告 
            _hideBottomImage = [[UIImageView alloc] initWithFrame:CGRectMake(0, size.height-67, ScreenWidth, 67)]; 
            _hideBottomImage.image = [UIImage imageNamed:@"banner"]; 
            [_webView.scrollView addSubview:_hideBottomImage]; 
            [_hideBottomImage release]; 
        } 
    } 
    else 
    { 
        //  调用父类的方法 
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context]; 
    } 
} 
 
- (void)dealloc{//---->在ARC环境下也能调用dealloc方法,只是不需要写[super dealloc] 
 
    // 移除KVO,否则会引起资源泄露  
    [_webView.scrollView removeObserver:self forKeyPath:@"contentSize"]; 
    [super dealloc];   
 
} 

//  ---定义一个Student类(.m文件无任何操作) 
#import <Foundation/Foundation.h> 
 
 
@class HMTClass; 
@interface HMTStudent : NSObject{ 
 
    NSString * _name; 
    
    BOOL _test; 
    BOOL _isTest; 
    BOOL test; 
    BOOL isTest; 
 
} 
 
@property (nonatomic,copy)NSString * name; 
@property (nonatomic,copy)NSString * sex; 
@property (nonatomic,assign)NSInteger age; 
@property (nonatomic,strong) HMTClass * hmtClass; 
 
@end 
 
//  ---main文件 
HMTStudent * student = [[HMTStudent alloc] init]; 
     
student.hmtClass = [[HMTClass alloc] init]; 
student.name = @"humingtao”;     //  set方法赋值
   
//  KVC赋值    
[student setValue:@“mawei is dog" forKey:@"name”];  
[student setValue:@"m" forKey:@"sex"]; 
[student setValue:@(10) forKey:@"age"]; 
//  取值     
NSLog(@"%s__%d__|%@",__FUNCTION__,__LINE__,[student valueForKey:@"name"]); 

//  创建一个班级类 
@interface HMTClass : NSObject 
 
@property (nonatomic,copy)NSString * name; 
 
@end 

 
HMTClass *hmtClass = [[HMTClass alloc]init]; 
[hmtClass setValue:@"宇宙一班" forKey:@"name"]; 
[student setValue:hmtClass forKey:@"hmtClass"]; 
NSString *hmtClassName = [student valueForKeyPath:@"hmtClass.name"]; 
 
//也可以这样存值 
[student setValue:@"宇宙一班" forKeyPath:@"hmtClass.name"]; 
student.hmtClass.name = [student valueForKeyPath:@"hmtClass.name"]; 

#import <Foundation/Foundation.h>   
@class HMTClass;   
@interface HMTStudent : NSObject   
{   
    NSString *_name;   
 
    NSInteger number;   
}   
@end   
 
[student setValue:@"100" forKeyPath:@"number"];   
NSString *number = [student valueForKey:@"number"];   

#import <Foundation/Foundation.h>   
@class HMTClass;   
@interface HMTStudent : NSObject   
{   
    NSArray *manyStudents;   
}   
@end   
           
Student *student1 = [[HMTStudent alloc]init];   
Student *student2 = [[HMTStudent alloc]init];   
Student *student3 = [[HMTStudent alloc]init];   
[student1 setValue:@"200" forKey:@"number"];   
[student2 setValue:@"300" forKey:@"number"];   
[student3 setValue:@"400" forKey:@"number"];   
NSArray *array = [NSArray arrayWithObjects:student1,student2,student3,nil];   
[student setValue:array forKey:@"manyStudents"];   
NSLog(@"%@",[student valueForKeyPath:@"manyStudents.number"]);