iOS传值方式：属性，代理，block，单例，通知

正向传值均可，反向传值除属性传值不可，其余均可。下面简单介绍：

（一）属性传值

第二个界面中的lable显示第一个界面textField中的文本

首先我们建立一个RootViewControllers和一个DetailViewControllers，在DetailViewControllers中声明一个textString属性，用于接收传过来的字符串，

同时创建一个Lable用来显示传过的字符串

在RootViewControllers上引入DetailViewControllers同时声明一个textField属性用来输入字符串

然后在RootViewControllers上我们创建并添加一个button，当点击button时响应相应方法进行视图间的切换完成视图间的传值

（二）Block传值

block传值也是从第一个界面给第二个界面传值

首先我们在DetailViewcontrollers的.h文件中，属性

在RootViewControllers的.m文件中，其他不变，在button的响应方法里我们为block属性赋值完成block传值

（三）代理传值

RootViewControllers页面push到DetailViewControllers页面，如果DetailViewControllers页面的信息想回传（回调）到RootViewControllers页面，用代理传值，其中DetailViewControllers定义协议和声明代理，RootViewControllers确认并实现代理，RootViewControllers作为DetailViewControllers的代理

首先在DetailViewControllers.h文件中我们创建协议方法

在DetailViewControllers的.m中我们判定代理对象存在时，为其绑定相应方法

RootViewControllers的.m文件中我们指定代理并让其执行代理的方法

（四）单例传值

单例传值（实现共享）

AppStatus.h  创建一个单例类 AppStatus

 1 #import <Foundation/Foundation.h>
 2
 3 @interface AppStatus : NSObject
 4 {
 5     NSString *_contextStr;
 6 }
 7
 8 @property(nonatomic,retain)NSString *contextStr;
 9
10 +(AppStatus *)shareInstance;
11
12 @end

AppStatus.m

 1 #import "AppStatus.h"
 2
 3 @implementation AppStatus
 4
 5 @synthesize contextStr = _contextStr;
 6
 7 static AppStatus *_instance = nil;
 8
 9 +(AppStatus *)shareInstance
10 {
11     if (_instance == nil)
12     {
13         _instance = [[super alloc]init];
14     }
15     return _instance;
16 }
17
18 -(id)init
19 {
20     if (self = [super init])
21     {
22
23     }
24     return self;
25 }
26
27 -(void)dealloc
28 {
29     [super dealloc];
30 }
31
32 @end

RootViewController.h

 1 #import "RootViewController.h"
 2 #import "DetailViewController.h"
 3 #import "AppStatus.h"
 4
 5 @interface RootViewController ()
 6
 7 @end
 8
 9 @implementation RootViewController
10
11 -(void)loadView
12 {
13     //核心代码
14     UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
15     btn.frame = CGRectMake(0, 0, 100, 30);
16     [btn setTitle:@"Push" forState:0];
17     [btn addTarget:self action:@selector(pushAction:) forControlEvents:UIControlEventTouchUpInside];
18     [self.view addSubview:btn];
19 }
20
21 -(void)pushAction:(id)sender
22 {
23     tf = (UITextField *)[self.view viewWithTag:1000];
24
25  //单例传值  将要传递的信息存入单例中（共享中）
26   //  [[AppStatus shareInstance]setContextStr:tf.text]; 跟下面这种写法是等价的
27     [AppStatus shareInstance].contextStr = tf.text;
28     //导航push到下一个页面
29     //pushViewController 入栈引用计数+1，且控制权归系统
30     DetailViewController *detailViewController = [[DetailViewController alloc]init];
31
32     //导航push到下一个页面
33     [self.navigationController pushViewController:detailViewController animated:YES];
34     [detailViewController release];
35 }
36
37 @end

DetailViewController.h

1 #import <UIKit/UIKit.h>
2 @protocol ChangeDelegate;//通知编译器有此代理
3
4 @interface DetailViewController : UIViewController
5 {
6     UITextField *textField;
7 }
8
9 @end

DetailViewController.m

 1 #import "DetailViewController.h"
 2 #import "AppStatus.h"
 3
 4 @interface DetailViewController ()
 5
 6 @end
 7
 8 @implementation DetailViewController
 9
10 @synthesize naviTitle = _naviTitle;
11
12 -(void)loadView
13 {
14     self.view = [[[UIView alloc]initWithFrame:CGRectMake(0, 0, 320, 480)]autorelease];
15
16     //单例
17     self.title = [AppStatus shareInstance].contextStr;
18     textField = [[UITextField alloc]initWithFrame:CGRectMake(100, 100, 150, 30)];
19     textField.borderStyle = UITextBorderStyleLine;
20     [self.view addSubview:textField];
21     [textField release];
22
23     UIBarButtonItem *doneItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDonetarget:self action:@selector(doneAction:)];
24     self.navigationItem.rightBarButtonItem = doneItem;
25     [doneItem release];
26 }
27
28 //这个方法是执行多遍的  相当于刷新view
29 -(void)viewWillAppear:(BOOL)animated
30 {
31     [super viewWillAppear:animated];
32     tf = (UITextField *)[self.view viewWithTag:1000];
33     tf.text = [AppStatus shareInstance].contextStr;
34 }
35
36 //pop回前一个页面
37 -(void)doneAction:(id)sender
38 {
39     //单例传值
40     [AppStatus shareInstance].contextStr = textField.text;
41     [self.navigationController popToRootViewControllerAnimated:YES];
42 } 

（五）通知传值

谁要监听值的变化，谁就注册通知  特别要注意，通知的接受者必须存在这一先决条件

A页面RootViewController.h

1 #import <UIKit/UIKit.h>
2 #import "DetailViewController.h"
3 @interface RootViewController : UIViewController<ChangeDelegate>
4 {
5     UITextField *tf;
6 }
7 @end 

A页面RootViewController.m

 1 #import "IndexViewController.h"
 2 #import "DetailViewController.h"
 3 #import "AppStatus.h"
 4
 5 @implementation IndexViewController
 6
 7 -(void)dealloc
 8 {
 9     [[NSNotificationCenter defaultCenter] removeObserver:self
10                                                     name:@"CHANGE_TITLE" object:nil];
11     [super dealloc];
12 }
13
14 -(id)init
15 {
16     if (self = [super init])
17     {
18         [[NSNotificationCenter defaultCenter] addObserver:self
19                                                  selector:@selector(change:)
20                                                      name:@"CHANGE_TITLE"
21                                                    object:nil];
22     }
23     return self;
24 }
25
26 -(void)change:(NSNotification *)aNoti
27 {
28     // 通知传值
29     NSDictionary *dic = [aNoti userInfo];
30     NSString *str = [dic valueForKey:@"Info"];
31
32     UITextField *tf =  (UITextField *)[self.view viewWithTag:1000];
33     tf.text = str;
34 }
35
36 -(void)viewWillAppear:(BOOL)animated
37 {
38     [super viewWillAppear:animated];
39     /*
40     // 单例传值
41     UITextField *tf =  (UITextField *)[self.view viewWithTag:1000];
42     tf.text = [AppStatus shareInstance].contextStr;
43     */
44 }
45
46 @end

DetailViewController.h

1 #import <UIKit/UIKit.h>
2 @protocol ChangeDelegate;//通知编译器有此代理
3
4 @interface DetailViewController : UIViewController
5 {
6     UITextField *textField;
7 }
8 @end

DetailViewController.m

 1 #import "DetailViewController.h"
 2 #import "AppStatus.h"
 3
 4 @implementation DetailViewController
 5 @synthesize naviTitle = _naviTitle;
 6
 7 -(void)loadView
 8 {
 9     UIBarButtonItem *doneItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDonetarget:self action:@selector(doneAction:)];
10     self.navigationItem.rightBarButtonItem = doneItem;
11     [doneItem release];
12 }
13
14 // pop回前一个页面
15 -(void)doneAction:(id)sender
16 {
17 NSDictionary *dic = [NSDictionary dictionaryWithObject:textField.text forKey:@"Info"];
18
19 [[NSNotificationCenter defaultCenter] postNotificationName:@"CHANGE_TITLE" object:nil userInfo:dic];
20
21 [self.navigationController popViewControllerAnimated:YES];
22
23 }