iOS 页面传值知多少？你真的了解吗？

iOS开发中，页面传值是很常见的，但是页面传值你究竟知道多少呢？笔者这篇文章就是给大家介绍一下页面传值的具体方式，有不足之处，欢迎大家指正，希望能和大家共同进步。说明一下：这里所说的正向、反向传值是指相关联的两个页面间的传值。

目前我所了解和掌握的传值方式有：属性传值、代理传值、Block传值、KVO传值、通知传值、单例传值、KVC传值。

下面我们来一一看下它们究竟是怎样进行操作和传值的呢？

假设我们现在有控制器（页面）A和控制器（页面）B，A->push->B，即A是B的上一个页面（控制器）。

属性传值
用法：正向传值
需求：当A-push到B时，B中有一个Label需要显示从A中的一个TextField输入的内容，这时我们需要用到正向传值。

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic, strong) UITextField *aTextField;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
    
     self.aTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.aTextField.layer.borderWidth = 1;
     [self.view addSubview:self.aTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 - (void)buttonAction:(UIButton *)sender {
 
     /**
      什么时候可以用 属性 传值
      
      A 传到 B，正向传值
      
      B 在 A页面 提前初始化
      
      **/
     
     B_ViewController *bViewController = [[B_ViewController alloc] init];
     bViewController.string = self.aTextField.text;
     [self.navigationController pushViewController:bViewController animated:YES];
     
 }

 @end

B控制器.h文件：

 #import <UIKit/UIKit.h>
 
 @interface B_ViewController : UIViewController
 
 @property (nonatomic, copy) NSString *string;
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"

 @interface B_ViewController ()
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     UILabel *bLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     bLabel.layer.borderColor = [UIColor grayColor].CGColor;
     bLabel.layer.borderWidth = 1;
     [self.view addSubview:bLabel];
     
     bLabel.text = self.string;
 }

 @end

代理传值
用法：反向传值：
需求：A-push到B，当B消失的时候，A中有一个Label需要显示从B中的一个TextField输入的内容，这时我们需要用到反向传值。

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController () <BToADelegate>
 
 @property (nonatomic, strong) UILabel *aLabel;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.aLabel.layer.borderColor = [UIColor grayColor].CGColor;
     self.aLabel.layer.borderWidth = 1;
     [self.view addSubview:self.aLabel];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"push到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 -(void)buttonAction:(UIButton *)sender {
    
     B_ViewController *bViewController = [[B_ViewController alloc] init];
     //设置代理
     bViewController.delegate = self;
     [self.navigationController pushViewController:bViewController animated:YES];
 }
 
 /**
  什么时候可以用 代理 传值
  
  B 传到 A，反向传值
  
  B 在 A页面 初始化
  
  设置A为B的代理
  
  执行代理方法
  
  **/
 - (void)transferString:(NSString *)string {
     
     self.aLabel.text = string;
 }
 
 @end

B控制器.h文件：

 #import <UIKit/UIKit.h>
 
 // 声明代理
 @protocol BToADelegate <NSObject>
 
 // 代理方法
 - (void)transferString:(NSString *)string;
 
 @end
 
 @interface B_ViewController : UIViewController
 
 // 代理属性
 @property (nonatomic, weak) id<BToADelegate> delegate;
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"
 
 @interface B_ViewController ()
 
 @property (nonatomic, strong) UITextField *bTextField;;
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     self.bTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.bTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.bTextField.layer.borderWidth = 1;
     [self.view addSubview:self.bTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 - (void)buttonAction:(UIButton *)sender {
     
     // 判断有没有代理以及代理是否响应代理方法
     if (self.delegate && [self.delegate respondsToSelector:@selector(transferString:)]) {
         [self.delegate transferString:self.bTextField.text];
     }
     
     [self.navigationController popToRootViewControllerAnimated:YES];
 }
 
 @end

Block传值
用法：反向传值：
需求：A-push到B，当B消失的时候，A中有一个Label需要显示从B中的一个TextField输入的内容，这时我们需要用到反向传值。

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic ,strong) UILabel *aLabel;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.aLabel.layer.borderColor = [UIColor grayColor].CGColor;
     self.aLabel.layer.borderWidth = 1;
     [self.view addSubview:self.aLabel];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"push到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 - (void)buttonAction:(UIButton *)sender {
 
     B_ViewController *bViewController = [[B_ViewController alloc] init];
 
     __weak __typeof(self) weakSelf = self;
     // block 回调接收
     [bViewController setBlock:^(NSString *string){
         weakSelf.aLabel.text = string;
     }];
     
     [self.navigationController pushViewController:bViewController animated:YES];
 }

B控制器.h文件：

 #import <UIKit/UIKit.h>
 
 // 定义一个block
 typedef void(^BToAblock)(NSString *string);
 
 @interface B_ViewController : UIViewController
 
 // block 属性
 @property (nonatomic, copy)BToAblock block;
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"
 
 @interface B_ViewController ()
 
 @property (nonatomic, strong) UITextField *bTextField;
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     self.bTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.bTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.bTextField.layer.borderWidth = 1;
     [self.view addSubview:self.bTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
 
 }
 
 - (void)buttonAction:(UIButton *)sender {
     /**
      Blcok 传值
         
      反向传值
      
      B 传到 A
      */
     _block(self.bTextField.text);
     [self.navigationController popToRootViewControllerAnimated:YES];
 }
 
 @end

KVO传值
用法：反向传值：
需求：A-push到B，当B消失的时候，A中有一个Label需要显示从B中的一个TextField输入的内容，这时我们需要用到反向传值。

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic, strong) UILabel *aLabel;
 @property (nonatomic, strong) B_ViewController *bViewController;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.aLabel.layer.borderColor = [UIColor grayColor].CGColor;
     self.aLabel.layer.borderWidth = 1;
     [self.view addSubview:self.aLabel];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"push到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
     /**
      KVO 创建 三步一定要写
         1. 注册观察者
         2. KVO的回调
         3. 移除观察者
      
      */
     
     // B 传到 A ，反向传值
     //注册观察者，注意：观察者的注册和移除要对应，如果移除时发现没有注册观察者，程序会crash
      self.bViewController = [[B_ViewController alloc] init];
     [self.bViewController addObserver:self forKeyPath:@"string" options:NSKeyValueObservingOptionNew context:nil];
 }
 
 - (void)buttonAction:(UIButton *)sender {
     
     [self.navigationController pushViewController:self.bViewController animated:YES];
     
 }
 
 // KVO的回调
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
     
     if ([keyPath isEqualToString:@"string"]) {
         self.aLabel.text = self.bViewController.string;
     }
     
 }
 // KVO 的移除方式  （和通知一样要移除）
 - (void)dealloc {
     
     [self.bViewController removeObserver:self forKeyPath:@"string"];
 }
 
 @end

B控制器.h文件：

 #import <UIKit/UIKit.h>
 
 @interface B_ViewController : UIViewController
 
 @property (nonatomic, copy) NSString *string;
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"
 
 @interface B_ViewController ()
 
 @property (nonatomic, strong) UITextField *bTextField;
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     self.bTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.bTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.bTextField.layer.borderWidth = 1;
     [self.view addSubview:self.bTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 - (void)buttonAction:(UIButton *)sender {
     // KVO
     // 把self.bTextfield.text 赋值给当前属性
     // 在A中 监听 当前属性
     self.string = self.bTextField.text;
     
     [self.navigationController popToRootViewControllerAnimated:YES];
 }
 
 @end

通知传值
用法：正向传值
需求：当A-push到B时，B中有一个Label需要显示从A中的一个TextField输入的内容，这时我们需要用到正向传值。

用法：反向传值：
需求：A-push到B，当B消失的时候，A中有一个Label需要显示从B中的一个TextField输入的内容，这时我们需要用到反向传值。

我们在此将两种传值情况写到一个Demo中，所以将上述Label换为Textfield即可，如下：

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic, strong) UITextField *aTextField;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];

     self.aTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.aTextField.layer.borderWidth = 1;
     [self.view addSubview:self.aTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
     // 接收通知
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(tzAction:) name:@"B2A" object:nil];
 }
 
 - (void)buttonAction:(UIButton *)sender {
 
     // 通知传值 一般是用于回传
     
     // 现在是 A传到B，正向传值
     
     // 发送通知的方法 要写在执行方法里面
     
     B_ViewController *bViewController = [[B_ViewController alloc] init];
     
     [[NSNotificationCenter defaultCenter] postNotificationName:@"A2B" object:nil userInfo:@{@"key":self.aTextField.text}];
     
     [self.navigationController pushViewController:bViewController animated:YES];
     
 }
 
 // 回调通知
 - (void)tzAction:(NSNotification *)sender {
     
     self.aTextField.text = sender.userInfo[@"key"];
 }
 
 // 移除通知
 - (void)dealloc {
     
     [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"
 
 @interface B_ViewController ()
 
 @property (nonatomic, strong) UITextField *bTextField;
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
 }
 
 //如果是从A传到B的话,B.m里要创建一个init方法,在里面写监听并在里面创建接收容器才能成功(因为程序先执行init方法再到viewDidLoad方法,当传值过去时在init就开始监听,如果这里没有创建textField接收,那就传不过去了,所以要在init里同时创建接收器(生命周期的问题));
 -(instancetype)init
 {
     if (self = [super init]) {

         [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(tzAction:) name:@"A2B" object:nil];
         
         self.bTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
        
         self.bTextField.layer.borderColor = [UIColor grayColor].CGColor;
         self.bTextField.layer.borderWidth = 1;
         [self.view addSubview:self.bTextField];
 
     }
 
     return self;
 }
 
 //接收通知
 - (void)tzAction:(NSNotification *)sender {
     
     self.bTextField.text = sender.userInfo[@"key"];
     
 }
 
 // 移除通知
 - (void)dealloc  {
     
     // 移除所有
     [[NSNotificationCenter defaultCenter] removeObserver:self];
     
     // 移除某个
     // [[NSNotificationCenter defaultCenter] removeObserver:self name:@"tz" object:nil];
 }
 
 //发送通知
 - (void)buttonAction:(UIButton *)sender {
     // B传到A，反向传值
     [[NSNotificationCenter defaultCenter] postNotificationName:@"B2A" object:nil userInfo:@{@"key":self.bTextField.text}];
     
     [self.navigationController popToRootViewControllerAnimated:YES];
     
 }
 
 @end

单例传值
用法：正向传值
需求：当A-push到B时，B中有一个Label需要显示从A中的一个TextField输入的内容，这时我们需要用到正向传值。

用法：反向传值：
需求：A-push到B，当B消失的时候，A中有一个Label需要显示从B中的一个TextField输入的内容，这时我们需要用到反向传值。

我们在此将两种传值情况写到一个Demo中，所以将上述Label换为Textfield即可，如下：

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 #import "DanLi.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic, strong) UITextField *aTextField;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     // Do any additional setup after loading the view.
     
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.aTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.aTextField.layer.borderWidth = 1;
     [self.view addSubview:self.aTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
 }
 
 - (void)viewWillAppear:(BOOL)animated
 {
     // 单例 传值 B传到A （可以双向传值）
     DanLi *danli = [[DanLi alloc] init];
     
     self.aTextField.text = danli.value;
 }
 
 - (void)buttonAction:(UIButton *)sender {
     
     // 单例 传值 A传到B （可以双向传值）
     DanLi *danli = [DanLi sharedDanLi];
     danli.value = self.aTextField.text;
  
     B_ViewController *bViewController = [[B_ViewController alloc] init];
 
     [self.navigationController pushViewController:bViewController animated:YES];
     
 }

B控制器.m文件：

 #import "B_ViewController.h"
 #import "DanLi.h"
 
 @interface B_ViewController ()
 
 @property (nonatomic, strong) UITextField *bTextField;
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     self.bTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.bTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.bTextField.layer.borderWidth = 1;
     [self.view addSubview:self.bTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
     self.bTextField.text = [DanLi sharedDanLi].value;
 }
 
 - (void)buttonAction:(UIButton *)sender {
     //B传给A
     [DanLi sharedDanLi].value = self.bTextField.text;
     [self.navigationController popToRootViewControllerAnimated:YES];
 }
 
 @end

单例类.h文件：

 #import <Foundation/Foundation.h>
 
 @interface DanLi : NSObject
 
 //创建一个单例//如果在单线程里可以用nonatomic,如果在多线程里一定要用atomic,保证是只有一个在调用,不然在多线程里面如果多个方法调用修改单例类里的属性时会冲突
 @property (atomic, copy) NSString *value;
 
 + (DanLi *)sharedDanLi;
 
 @end

单例类.m文件：

 #import "DanLi.h"
 
 static DanLi *danli = nil;
 
 @implementation DanLi
 
 //实现方法,判断是否为空,是就创建一个全局实例给它
 + (DanLi *)sharedDanLi {
     
     if (danli == nil) {
         danli = [[DanLi alloc] init];
     }
     return danli;
 }
 
 //避免alloc/new创建新的实例变量--->增加一个互斥锁
 + (id)allocWithZone:(struct _NSZone *)zone {
     
     @synchronized(self) {
         if (danli == nil) {
             danli = [super allocWithZone:zone];
         }
     }
     return danli;
 }
 
 //避免copy,需要实现NSCopying协议
 - (id)copyWithZone:(NSZone *)zone {
     return self;
 }
 
 @end

KVC传值
用法：正向传值
需求：当A-push到B时，B中有一个Label需要显示从A中的一个TextField输入的内容，这时我们需要用到正向传值。

A控制器.m文件：

 #import "A_ViewController.h"
 #import "B_ViewController.h"
 
 @interface A_ViewController ()
 
 @property (nonatomic, strong) UITextField *aTextField;
 
 @end
 
 @implementation A_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     // Do any additional setup after loading the view.
     self.title = @"A";
     self.view.backgroundColor = [UIColor whiteColor];
     self.aTextField = [[UITextField alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     self.aTextField.layer.borderColor = [UIColor grayColor].CGColor;
     self.aTextField.layer.borderWidth = 1;
     [self.view addSubview:self.aTextField];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传到B" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
 }

 - (void)buttonAction:(UIButton *)sender {
 
     B_ViewController *bViewController = [[B_ViewController alloc] init];
 
     /**
         KVC 传值：这里只能传A传到B （因为 B在A页面提前初始化）
         B 有个属性 string
         用B对象 给B属性赋值（回顾下OC中KVC赋值 就理解了）
      
         这里forkey 一定要和B 属性名字一致 （也可以用@"_string"）因为是属性
      */
     
     // 给B属性string  赋值
     [bViewController setValue:self.aTextField.text forKey:@"string"];
     
     [self.navigationController pushViewController:bViewController animated:YES];
 }
 
 @end

B控制器.h文件：

 #import <UIKit/UIKit.h>
 
 @interface B_ViewController : UIViewController
 
 @property (nonatomic, copy) NSString *string;
 
 @end

B控制器.m文件：

 #import "B_ViewController.h"
 
 @interface B_ViewController ()
 
 @end
 
 @implementation B_ViewController
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     
     self.title = @"B";
     self.view.backgroundColor = [UIColor whiteColor];
     
     self.view.backgroundColor = [UIColor whiteColor];
     UILabel *bLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 200, 100, 30)];
     
     bLabel.layer.borderColor = [UIColor grayColor].CGColor;
     bLabel.layer.borderWidth = 1;
     [self.view addSubview:bLabel];
     
     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
     button.frame = CGRectMake([UIScreen mainScreen].bounds.size.width/2-50, 280, 100, 30);
     [button setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
     [button setTitle:@"传值A" forState:UIControlStateNormal];
     [button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
     [self.view addSubview:button];
     
     // KVC 接收值
     bLabel.text = self.string;
 }
 
 - (void)buttonAction:(UIButton *)sender {
     
     [self.navigationController popToRootViewControllerAnimated:YES];
 }
 
 @end

好了，到此已经基本上介绍完页面传值了，相信你对页面传值已经有一定理解了吧，快去实践吧！

最后编辑于：2017.12.03 04:39:08

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