What is KVC and KVO

------------------KVC--------------
Character.h

#import <Foundation/Foundation.h>

@interface Character : NSObject
{
    NSString *Name;
    NSInteger Rating;
}

@property (nonatomic, copy) NSString *Name;

@property(nonatomic, assign) NSInteger Rating;

@end

Character.m

#import "Character.h"

@implementation Character

@synthesize Name;

@synthesize Rating;

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if([keyPath isEqualToString:@"required"])
    {

        //NSLog(@"%@",[object valueForKeyPath:keyPath]);

         NSLog(@"%@",[change  objectForKey:NSKeyValueChangeOldKey]);
    }
}

@end

-(void)KVC

{

    Character *conharector1;    

    // KVC...

    conharector1 = [[Character alloc] init];

    [conharector1 setValue:@"Amit" forKey:@"Name"];

    [conharector1 setValue:[NSNumber numberWithInt:10] forKey:@"Rating"];

    

    //Done! 

    

    NSString *GetconharectorName = [conharector1 valueForKey:@"Name"];

    NSNumber *GetconharectorRating = [conharector1 valueForKey:@"Rating"];

    

    NSLog(@"%@ Rating = %d  ", GetconharectorName, [GetconharectorRating intValue]);

    

}

OUTPUT :

2013-05-16 10:58:20.263 StoryBoardApplication[536:c07] Amit Rating = 10  

----------------------- KVO---------------

Employee.h

#import <Foundation/Foundation.h>

@interface Employee : NSObject

{

    int required;

}

@property(nonatomic,assign) int required;

-(id)init;

@end

Employee.m

#import "Employee.h"

@implementation Employee

@synthesize required;

-(id)init
{

     self = [super init];

    if(self)
    {
        required = 1;
    }

    return self;

}

@end

Manager.h

import <Foundation/Foundation.h>

@interface Manager : NSObject

@end

Manager.m

#import "Manager.h"

@implementation Manager

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

    if([keyPath isEqualToString:@"required"])

    {

        //NSLog(@"%@",[object valueForKeyPath:keyPath]);

        NSLog(@"%@",[change  objectForKey:NSKeyValueChangeNewKey]);

        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Changed" message:@"Required value has changed By Employee" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];

        [alert show];

    }

}

@end

Following method you can call whereever you want to :

-(void)KVO

{

    Employee *employee = [[Employee  alloc]init];

    Manager *manager = [[Manager alloc]init];

    

    [employee addObserver:manager forKeyPath:@"required" options:NSKeyValueObservingOptionNew   context:NULL];

    [employee setRequired:67];

    [employee removeObserver:manager forKeyPath:@"required"];

    

} 

OUTPUT :

2013-05-16 10:56:25.601 StoryBoardApplication[512:c07] 67

and an alert like : Required value has changed By Employee

I hope it will be help you....