多控制器管理

- ( IBAction )back:( UIButton *)sender
{
    // 通过展示控制器关闭当前窗口
    [ self . presentingViewController dismissViewControllerAnimated : YES completion : nil ];
   

}

-( void )prepareForSegue:( UIStoryboardSegue *)segue sender:( id )sender
{
    NSLog ( @"%@" ,segue. identifier );
    if ([segue. identifier isEqualToString : @"modal" ])
    {
        SecondViewController *second =segue. destinationViewController ;
       
        second. text = @"welcome to you" ;

    }

}

// 定义反向传数据的代理协议
@protocol SecondViewControllerDelegate
-( void )comeback:( NSString *)str;

@end

// 定义协议

@property ( weak , nonatomic ) id < SecondViewControllerDelegate >delegate;

// 通过代理反向传数据

    [self.delegate comeback:@"Tom"];

  UIViewController < SecondViewControllerDelegate >

  second. delegate = self ;

// 成为消息的观察者

[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(comeback:) name:SECONDVIEWCONTROLLERNOTIFICATION object:nil];

// 取消观察者

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

// 通过通知方式反向传数据

[[NSNotificationCenter defaultCenter]postNotificationName:SECONDVIEWCONTROLLERNOTIFICATION object:nil userInfo:@{SECONDVIEWCONTROLLERNOTIFICATIONKey:@"Tom"}];

// 从通知对象取出数据

NSDictionary *data = notification.userInfo;

self . Label . text = [data objectForKey : SECONDVIEWCONTROLLERNOTIFICATIONKey ];