iOS开发——block传值

淡淡的烟草味﹌ 2022-08-21 06:51 173阅读 0赞

要实现界面之间值得传递，有两种方法，一种是利用代理传值，另一种是利用block传值。  
Apple 官方文档中是这样介绍block的，A block is an anonymous inline collection of code，and sometimes also called a “closure”.block是个代码块，但可以将他当做一个对象处理。下面就举个利用block实现界面间的传值。

本例说明：（firstView 的lablel文本初始值是first，当点击按钮进行页面跳转之后进入secondView的时候，此时block改变firstView中label的文本值为second）

firstView.m

- (void)viewDidLoad {
        [super viewDidLoad];
        self.view.backgroundColor = [UIColor yellowColor];
    
        //创建一个Label，用于观察block调用前后label.text的变化
        UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(50, 50, 300, 100)];
        label.text = @"first";
        self.label = label;
        [self.view addSubview:self.label];
    
    
        //创建一个button实现界面间的跳转
        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
        button.frame = CGRectMake(50, 150, 150, 100);
    
        [button setTitle:@"To secondView" forState:UIControlStateNormal];
    
        [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];
    
        [self.view addSubview:button];
    }
    
    -(void)buttonPressed
    {
        SecondViewController *secondView = [[SecondViewController alloc] init];
    
        //block声明的同时赋值
        secondView.myBlock = ^(NSString *color){
            self.label.text = color;
        };
    
        //跳转到secondView的实现方法
        [self presentViewController:secondView animated:YES completion:nil];
    }

secondView.h

#import <UIKit/UIKit.h>
    
    @interface SecondViewController : UIViewController
    
    //block属性
    @property(nonatomic,strong)void(^myBlock)(NSString *color);
    
    @end

secondView.m

- (void)viewDidLoad {
        [super viewDidLoad];
        // Do any additional setup after loading the view.
    
        self.view.backgroundColor = [UIColor greenColor];
    
        //创建一个按钮，用于返回firstView
        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
        button.frame = CGRectMake(50, 150, 150, 100);
    
        [button setTitle:@"cancle" forState:UIControlStateNormal];
    
        [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];
    
        [self.view addSubview:button];
    
        //调用myBlock，传入second参数
        self.myBlock(@"second");
    }
    
    
    -(void)buttonPressed
    {
        //返回之前的控制器
        [self dismissViewControllerAnimated:YES completion:nil];
    }

运行代码，结果如下：

开始的firstView界面  
![开始的界面][20160421222523613]  
点击按钮后跳转到secondView  
![跳转之后][20160421222605100]  
点击按钮返回firstView，可看到label文本从first改变成了second  
![返回之后][20160421222618629]

[20160421222523613]: /images/20220724/04ec6f27fb9d4280b1671b47251a0398.png
[20160421222605100]: /images/20220724/3325bd03b4e546568fa6b8da5b6396c7.png
[20160421222618629]: /images/20220724/cd5bd60bce0640f0b82f7c44b5c73344.png