iOS如何实现两个控制器之间数据的双向传递

#import 

@interface FirstViewController : UIViewController

@end

#import "FirstViewController.h"
#import "SecondViewController.h"

@interface FirstViewController ()

/** 用于写入数据，最后该数据用于传递给第二个界面 */
@property (weak, nonatomic) IBOutlet UITextField *first2Second;
/** 用于显示第二个界面返回来时传递的数据 */
@property (weak, nonatomic) IBOutlet UITextField *displayWithSecond;

@end

@implementation FirstViewController

- (void)viewDidLoad {
  [super viewDidLoad];

}

#pragma mark - Navigation

//点击传递按钮时会自动调用此方法
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
  SecondViewController *vc = (SecondViewController *)segue.destinationViewController;
  if (self.first2Second.text.length > 0) {
    //将该界面中的数据传递给第二个界面
    vc.name = self.first2Second.text;
  }

  //设置当前控制器为SecondViewController控制器的代理
  vc.delegate = self;
}

#pragma mark - 实现SecondViewControllerDelegate中的协议方法
-(void)secondViewControllerDidDit:(SecondViewController *)viewController andName:(NSString *)name
{
  //将第二个界面中的数据返回给第一个界面（此界面）
  self.displayWithSecond.text = name;
}

@end

#import 
@class SecondViewController;

@protocol SecondViewControllerDelegate 

/** SecondViewControllerDelegate协议中的方法 */
-(void)secondViewControllerDidDit:(SecondViewController *)viewController andName:(NSString *)name;

@end

@interface SecondViewController : UIViewController

@property(nonatomic,strong) NSString *name;
@property(nonatomic,weak) id delegate;

@end

#import "SecondViewController.h"

@interface SecondViewController ()
/** 用于写入数据，最后将数据返回给第一个界面 */
@property (weak, nonatomic) IBOutlet UITextField *second2First;
/** 用于显示第一个界面传过来的数据 */
@property (weak, nonatomic) IBOutlet UITextField *displayWithFirst;
/** 点击此按钮，第二个控制器将弹出栈，界面将返回到第一个界面 */
- (IBAction)second2First:(UIButton *)sender;

@end

@implementation SecondViewController

- (void)viewDidLoad {
  [super viewDidLoad];

  //显示第一个界面传递过来的数据信息
  self.displayWithFirst.text = self.name;

}

//点击该按钮，数据将返回给第一个界面显示
- (IBAction)second2First:(UIButton *)sender {
  if (self.second2First.text.length > 0) {
    //如果有实现该协议方法的控制器，则将数据传给该控制器
    if ([self.delegate respondsToSelector:@selector(secondViewControllerDidDit:andName:)]) {
      [self.delegate secondViewControllerDidDit:self andName:self.second2First.text];
    }
  }
  [self.navigationController popViewControllerAnimated:YES];
}

@end