实现效果:

搭建两个页面, 两个页面中分别添加一个Label和一个TextField控件, 实现前后单例传值操作
Label1———>TextField2
Label2———>TextField1

*重点部分,单例类的建立

<<DataHandle.h文件>>

#import <Foundation/Foundation.h>
@interface DataHandle : NSObject

//给单例添加一个属性, 用来传值
@property (strong, nonatomic) NSString *text;
//定义一个初始化单例的方法
+ (instancetype)sharedDataHandel;

@end

<<DataHandle.m文件>>

//写单例的原因, 是希望在程序的运行期间, 他在内存中一直存在, 可以随时读取数据
static DataHandle *dataHandle = nil;
@implementation DataHandle
//创建单例方法使用加号的原因: 在创建之前无法存在一个实例对象去去调用
+ (instancetype)sharedDataHandel{
     //为了线程安全(添加线程锁)
    static dispatch_once_t onceToken;    
    dispatch_once(&onceToken, ^{           
         if (!dataHandle) {                
              dataHandle = [[DataHandle alloc] init];     
           }       
    });   
     return dataHandle;
}
//第二种方法
//+(instancetype)sharedDataHandle{
//为了线程安全(添加线程锁)
//    @synchronized(self) {
//        if (!dataHandle) {
//              dataHandle = [[DataHandle alloc] init];
//        }
//     }
//     return dataHandle; 
//}
@end

*新建两个viewController , 实现两个ViewController页面的跳转传值

<<FirstViewController.m文件>>

#import "FirstViewController.h"
#import "SecondViewController.h"
#import "DataHandle.h"
@interface FirstViewController ()
@property (strong, nonatomic) UILabel *label;
@property (strong, nonatomic) UITextField *textField;
@end
@implementation FirstViewController
- (void)viewDidLoad {    
    [super viewDidLoad];      
   self.view.backgroundColor = [UIColor colorWithRed:0.595 green:0.955 blue:1.000 alpha:1.000];    
   self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"next" style:(UIBarButtonItemStylePlain) target:self action:@selector(nextAC)];       
   self.label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 200, 40)];          
   self.label.backgroundColor = [UIColor orangeColor];   
   [self.view addSubview:self.label];       
   self.textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 150, 200, 60)];      
   self.textField.backgroundColor = [UIColor orangeColor];
   [self.view addSubview:self.textField];
}

//将从后往前的传值, 放到该方法中是因为ViewDidLoad方法只加载一遍
- (void)viewWillAppear:(BOOL)animated{        
    self.label.text = [DataHandle sharedDataHandel].text;
   }
- (void)nextAC{       
          SecondViewController *secondVC = [SecondViewController new];
          //传值
          DataHandle *dataHandle = [DataHandle sharedDataHandel];
          dataHandle.text = self.textField.text;      
          [self.navigationController pushViewController:secondVC animated:YES];   
   }
}

@end

<<SecondViewController.m文件>>

#import "SecondViewController.h"
#import "DataHandle.h"
@interface SecondViewController ()
@property (strong, nonatomic) UILabel *label;
@property (strong, nonatomic) UITextField *textField;
@end
@implementation SecondViewController
- (void)viewDidLoad {   
     [super viewDidLoad];         
     self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"back" style:(UIBarButtonItemStylePlain) target:self action:@selector(backAC)];      
     self.view.backgroundColor = [UIColor colorWithRed:1.000 green:0.399 blue:0.584 alpha:1.000];       
     self.label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 200, 40)];    
     self.label.backgroundColor = [UIColor colorWithRed:0.680 green:1.000 blue:0.618 alpha:1.000];   
     [self.view addSubview:self.label];          
     self.textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 150, 200, 60)];    
     self.textField.backgroundColor = [UIColor colorWithRed:0.800 green:1.000 blue:0.653 alpha:1.000];   
     [self.view addSubview:self.textField];
    
      //取值
      DataHandle *dataHandle = [DataHandle sharedDataHandel];  
      self.label.text = dataHandle.text;
}
- (void)backAC{
          //传值
          DataHandle *dataHandle = [DataHandle sharedDataHandel];    
          dataHandle.text = self.textField.text;      
          [self.navigationController popViewControllerAnimated:YES];
  }

@end```