Controller之间传递数据：协议传值

http://itjoy.org/?p=416

      前边介绍过从第一个页面传递数据到第二个页面，那么反过来呢我们该如何操作？还是同一个例子，将第二个页面的字符串传递到第一个页面显示出来，这中形式就可以使用协议来传值，协议我们可以理解成双方规定好一组标准，都满足这个标准我们之间就可以通信，一方通过协议发送数据，另一方通过协议来接受数据。

代码如下：从Second传递数据到First

 

 

 

 

 

Objective-C

 

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///////////////////////// /////////FirstViewController.h//////////// #import <UIKit/UIKit.h> #import "SecondViewController.h"   @interface FirstViewController : UIViewController<UITextFieldDelegate,SendMessage>  //遵守SendMessage协议 @property (nonatomic, retain) UILabel *nameLable; @end   ///////////FirstViewController.m - (void)viewDidLoad {     [super viewDidLoad];          self.nameLable = [[[UILabel alloc]initWithFrame:CGRectMake(10, 10, 300, 60)]autorelease];     self.nameLable.textAlignment = UITextAlignmentCenter;     self.nameLable.font = [UIFont systemFontOfSize:50];     self.nameLable.textColor = [UIColor blueColor];     [self.view addSubview:self.nameLable];            UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];     button.frame = CGRectMake(130, 170, 60, 40);     [button setTitle:@"下一个" forState:UIControlStateNormal];     [button addTarget:self action:@selector(pushNext:) forControlEvents:UIControlEventTouchUpInside];     [self.view addSubview:button]; }   - (void)pushNext:(id)sender {     //初始化second     SecondViewController *second = [[SecondViewController alloc]init];     //设置代理，由谁去执行     second.delegate = self;     //推过去     [self.navigationController pushViewController:second animated:YES];     [second release]; } //实现协议的方法 - (void)sendValue:(NSString *)str {     //赋值操作     self.nameLable.text = str; }

 

 

 

 

 

Objective-C

 

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//////////////////////// //////////////////SecondViewController.h #import <UIKit/UIKit.h> @protocol SendMessage;   @interface SecondViewController : UIViewController<UITextFieldDelegate> @property(nonatomic, assign)id<SendMessage> delegate; @end   ///协议的定义，包含一个方法。 @protocol SendMessage <NSObject>   - (void)sendValue:(NSString *)str;   @end /////////////SecondViewController.m - (void)viewDidLoad {     [super viewDidLoad];          UITextField *textFd = [[UITextField alloc]initWithFrame:CGRectMake(10, 10, 300, 150)];     textFd.borderStyle = UITextBorderStyleRoundedRect;     textFd.delegate = self;     textFd.tag = 100;     [self.view addSubview:textFd];     [textFd release]; }   - (BOOL)textFieldShouldReturn:(UITextField *)textField {     [textField resignFirstResponder];     //如果delegate 是这个类型的就调用这个方法，类似于java中的接口，子类实现接口，可以调用接口中的方法     if ([self.delegate conformsToProtocol:@protocol(SendMessage) ]) {         [self.delegate sendValue:textField.text];     }     return YES; }