前言

• iOS传值方法多种多样，之前学习了-属性传值- KVO传值—协议传值
• 今天了解了Block传值

Block传值

案例分析

• 设置2个View界面，View Second向ViewFrist传值

VIew Second要写的

• SecondViewController.h

自定义一个Block属性

• 设置按钮和函数

// 自定义Block属性
typedef void(^block) (NSString* secondString);

@interface SecondViewController : UIViewController
// 要传过去的字符串
@property (nonatomic, strong)NSString* string;
// 点击到第一界面
@property (nonatomic, strong)UIButton* nextButton;

// 定义block属性
@property (nonatomic, copy)block myBlock;
@end
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• ** "SecondViewController.m"**
• • 点击函数里面传入我们要传过去的字符串string- _myBlock(_string);

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor orangeColor];
    self.title = @"有代码块的界面";
    
    // 需要传过去的字符串
    _string = [NSString stringWithFormat:@"被传过去的字符串"];
    
    _nextButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [_nextButton setTitle:@"到达一级界面" forState:UIControlStateNormal];
    _nextButton.frame = CGRectMake(0, 0, 200, 200);
    [_nextButton addTarget:self action:@selector(pressButton) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:_nextButton];
    
}
// 点击按钮事件的时候返回第一界面，并传值给代码块
- (void)pressButton {
    _myBlock(_string);
    [self dismissViewControllerAnimated:YES completion:nil];
    
}
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ViewController写的

• ViewController.h

@interface ViewController : UIViewController
@property (nonatomic ,strong) UILabel* label;
@property (nonatomic, strong) UIButton* lastButton;

@end


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• ViewController.m
• • • 点击界面获取上一个界面传过来的string，赋值给该界面的label.text

#import "ViewController.h"
#import "SecondViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    _label = [[UILabel alloc] init];
    _label.font = [UIFont systemFontOfSize:21];
    _label.frame = CGRectMake(100, 300, 200, 30);
    [self.view addSubview:_label];
    
    _lastButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [_lastButton setTitle:@"跳转到第二界面" forState:UIControlStateNormal];
    [_lastButton addTarget:self action:@selector(pressButton) forControlEvents:UIControlEventTouchUpInside];
    _lastButton.frame = CGRectMake(100, 400, 200, 30);
    [self.view addSubview:_lastButton];
}

- (void)pressButton {
    SecondViewController* View = [[SecondViewController alloc] init];
    // 获取上一个界面的block 传给label
    View.myBlock = ^(NSString* str) {
        self.label.text = str;
    };
    [self presentViewController:View animated:YES completion:nil];
    
    
}
@end

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效果图

• 点击跳转到第二界面点击跳回然后传入string在第一界面显示即意味着完成了传值

总结

我认为Block传值和协议传值的目的都是底下向外传，block是在二级界面自定义代码块，然后在二级界面的点击函数里传入需要的东西，一级界面在跳转的时候接受传值即可完成。
协议传值详解