ios开发中传值方式一:block传值(支持逆向传值,不支持顺序传值!!!)

传值方式一:block传值 (仅支持逆向传值).

本例子是在firstViewController(firstVC)里面创建 UILabel * lab ,和提交按钮. 在secondViewControlloer(secondVC) 里面创建UITextField * textField; 和返回按钮.实现在secondVC界面的textField里面输入文字点击返回按钮之后在firstVC里面的lab上面显示textFied里面输入的文字.(我是在项目中直接拖得控件)

1,在secondViewController视图控制器的.h文件里面完成block的定义和声明.

　　secondViewController.h

 1 #import <UIKit/UIKit.h>
 2 
 3 
 4 typedef void (^ReturnBlock)(NSString * text);//为声明的block定义一个名字ReturnBlock
 5 
 6 @interface secondViewController : UIViewController
 7 /* @property(weak,nonatomic)NSString * str;//这个没用 */
 8 
 9 @property(copy,nonatomic)ReturnBlock returnBlock;//定义一个block为secondVC的属性
10 
11 -(void)backText:(ReturnBlock)block;//block执行的代码块
12 
13 @end

2,在secondViewController里面实现方法

　　secondViewController.m

 1 #import "secondViewController.h"
 2 
 3 @interface secondViewController ()
 4 
 5 
 6 @property (weak, nonatomic) IBOutlet UITextField *textField;
 7 @end
 8 
 9 @implementation secondViewController
10 
11 - (void)viewDidLoad {
12     [super viewDidLoad];
13     // Do any additional setup after loading the view from its nib.
14     self.view.backgroundColor = [UIColor yellowColor];
15 }
16 - (IBAction)btnClick:(id)sender {
17     [self.navigationController popToRootViewControllerAnimated:YES];
18 }
19 //把传进来的代码块保存到本类的实例变量returnBlock中
20 -(void)backText:(ReturnBlock)block{
21     self.returnBlock = block;
22 }
23 //在视图控制器将要消失的时候调用
24 -(void)viewWillDisappear:(BOOL)animated{
25     if (_textField.text != nil) {
26         self.returnBlock(_textField.text);
27     }
28 }

3,在firstViewController里面的按钮点击方法里面实现 (这里有点疑问为什么必须在第一个视图控制器里面的按钮方法里面实现??? 希望知道的可以跟我留言谢谢!!)

　　firstViewController.m

 1 #import "firstViewController.h"
 2 #import "secondViewController.h"
 3 
 4 @interface firstViewController ()
 5 @property (weak, nonatomic) IBOutlet UILabel *lab;
 6 
 7 @end
 8 
 9 @implementation firstViewController
10 
11 - (void)viewDidLoad {
12     [super viewDidLoad];
13     // Do any additional setup after loading the view from its nib.
14     self.view.backgroundColor= [UIColor greenColor];
15 }
16 - (IBAction)btnClick:(id)sender {
17     secondViewController * secondVC = [[secondViewController alloc]init];
18     [secondVC backText:^(NSString *text) {
19         _lab.text = text;
20     }];
21     [self.navigationController pushViewController:secondVC animated:YES];
22     
23 }

这样就可以实现 block传值了! ^_^