IOS-NSNotification的简单使用流程：

NSNotification的简单使用流程（例子）如下：

1、在viewDidLoad添加：

- (void)viewDidLoad
{//添加如下

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(showAlertView:) name:@"showAlertView" object:nil];

}

2、.m文件中添加：（例子如下）

- (void)showAlert:(NSString *)msg
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Note" message:msg delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
    [alert show];
    [alert release];
}
- (void)showAlertView:(NSNotification *)notification
{
    if (self.pickerView.getIndex <= 2) {
        [self showAlert:@"Number of players has reached its minimum."];
    }else if (self.pickerView.getIndex >= 50) {
        [self showAlert:@"Number of players has reached its maximum."];
    }
}

3、在需要响应并发出通知处，调用如下方法：

- (void)sendNotification{
        if ([self getIndex] >= 50)
            [[NSNotificationCenter defaultCenter] postNotificationName:@"showAlertView" object:nil];
        if ([self getIndex] <= 2)
            [[NSNotificationCenter defaultCenter] postNotificationName:@"showAlertView" object:nil];
}

4、在viewDidUnLoad添加：

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

5、在dealloc中添加：

    [[NSNotificationCenter defaultCenter] removeObserver:self name:nil object:nil];