iOS开发——block传值

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

点击按钮后跳转到secondView

点击按钮返回firstView，可看到label文本从first改变成了second