即时改变badgeValue的值（使用KVO）

首先先创建一个类

Number

@interface Number : NSObject
{
    NSNumber *badgeValue_number;    //属性
}
@end

YcwAppDelegate.h文件内

@property (retain, nonatomic)Number *ycwNumber;

YcwAppDelegate.m文件内

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen]bounds]];
    
    YcwViewController *view = [[YcwViewController alloc]initWithNibName:@"YcwViewController" bundle:nil];
    YcwSecondViewController *secondView = [[YcwSecondViewController alloc]initWithNibName:@"YcwSecondViewController" bundle:nil];
    
    YcwThirdViewController *thirdView = [[YcwThirdViewController alloc]initWithNibName:@"YcwThirdViewController" bundle:nil];
    NSArray *array_controllers =[NSArray arrayWithObjects:view,secondView,thirdView, nil];
    
    UITabBarController *tabBarController = [[UITabBarController alloc]init];
    tabBarController.viewControllers = array_controllers;
    
    self.window.rootViewController = tabBarController;
    
    [self.window makeKeyAndVisible];
    
    
    self.ycwNumber = [[Number alloc]init];
    
    return YES;
}

创建一个视图YcwViewController  添加一个button事件

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.tabBarItem.title = @"first";
        self.tabBarItem.image = [UIImage imageNamed:@"111.png"];
    }
    return self;
}

- (IBAction)buttonAction:(id)sender {
    
    int i = [[delegate.ycwNumber valueForKey:@"badgeValue_number"] intValue];
    
    i = i+1;
    
    [delegate.ycwNumber setValue:[NSNumber numberWithInt:i] forKey:@"badgeValue_number"];
    
    
}

创建一个视图YcwThirdViewController  

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.tabBarItem.title = @"third";
        self.tabBarItem.image = [UIImage imageNamed:@"333.png"];
        
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    delegate = [[UIApplication sharedApplication]delegate];
    [delegate.ycwNumber addObserver:self forKeyPath:@"badgeValue_number" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
    
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    
    
    if ([keyPath isEqualToString:@"badgeValue_number"]) {
        self.tabBarItem.badgeValue = [NSString stringWithFormat:@"%@",[delegate.ycwNumber valueForKey:@"badgeValue_number"]];

    }
    
    
}