附：注册键盘升启关闭消息 //键盘升起  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil]; //键盘降下 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];

消息傳送机构:举例说明

在有需要的类中，发送消息
//发送消息出去，这里的对象是一个数组：saveImageArray
[[NSNotificationCenter defaultCenter] postNotificationName:@"postData" object:saveImageArray];

所有亲朋好友给我给包(发送消息)，，，

//注册一个observer来响应消息的传送
[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(PostImage:)//接收消息方法
                                                 name:@"postData"//消息识别名称
                                               object:nil];
                                               
举个例子，过年了，准备一个大的钱包(注册一个OBserver)，嘿嘿，，，，                                               
            
                
                                   
                        
//实现方法            
-(void)PostImage:(NSArray *)array
{
    //接收传送过来的消息
}

我把红包都收起来，（接收消息）            
                
                
                    
                                               
//移除observer                                           
[[NSNotificationCenter defaultCenter] removeObserver:self name:@"postData" object:nil];
红包都收完了，哈哈，亲朋好友回家咯。。

简单说明，哈哈，不需要理解太复杂。。。。

例说明：KVC用来传送消息，是很不错的。

//kvo注册以parserDatas为例说明：parserDatas是一个解析XML的类
[parserDatas addObserver:self forKeyPath:@"isFinished"    options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:parserDatas];

//接收变更通知
- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context{
    
    if ([keyPath isEqual:@"isFinished"]) {
        BOOL isFinished=[[change objectForKey:NSKeyValueChangeNewKey] intValue];
        if (isFinished) {//如果服务器数据接收完毕
            
            NSMutableArray *array = [[NSMutableArray alloc] init];
            [array addObjectsFromArray:parserDatas.parsedDataArray];
            //保存数据
            [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
            NSString *path = [DOCUMENT_PATH stringByAppendingPathComponent:@"AllXmlDataArray.bin"];
            [NSKeyedArchiver archiveRootObject:array toFile:path];
            [array release];
            //取消kvo注册
            [object removeObserver:self
                     forKeyPath:@"isFinished"];
        }      
    }else{
        // be sure to call the super implementation
        // if the superclass implements it
        [super observeValueForKeyPath:keyPath
                             ofObject:object
                               change:change
                              context:context];
    }
}

在parserDatas类中定义：

+ (BOOL):(NSString*)key
{
    //当这两个值改变时，使用自动通知已注册过的观察者，观察者需要实现observeValueForKeyPath:ofObject:change:context:方法
    if ([key isEqualToString:@"isFinished"])
    {
        return YES;
    }
    return [super automaticallyNotifiesObserversForKey:key];
}

发送变更通知：

在需要跟踪消息记录的函数中加入：
[self setValue:[NSNumber numberWithBool:YES] forKey:@"isFinished"];

[[NSNotificationCenter defaultCenter] removeObserver:self name:@"saveMessage" object:nil];

不用的时候，才注销掉的。。

一般放在dealloc....里面。

在用之前把notification注册掉，是为了防止多次注册，这一般是因为这个view在程序运行时要load很多次，比如Three20的非顶层的View每次显示的时候都重新load，这样如果不在用之前把notification注册掉，就会重复注册消息，比如每次接收到消息就打印一句话，当你打开了n次这个view的时候，这句话就会打印n次...

- (void)awakeFromNib{

[[NSNotificationCenter defaultCenter] addObserver:self

selector:@selector(switchViews:)

name:@"switchViews"

object:nil];

}

- (void)switchViews:(NSNotification*)notification{

NSNumber *viewNumber = [notification object];

NSInteger i = [viewNumber integerValue];

[self setSelectedSegmentIndex:i];

UIView *chosenView = nil;

switch (i) {

case 0:

chosenView = view1;

break;

case 1:

chosenView = view2;

break;

case 2:

chosenView = view3;

break;

default:

break;

}

if (chosenView) {

[[viewController view] bringSubviewToFront:chosenView];

}

}

- (void)dealloc{

[super dealloc];

[[NSNotificationCenter defaultCenter] removeObserver:self];

}

@end