iOS开发之利用Block逆向传值

//.h 文件

/**
 *  类型自定义
 */
typedef void (^ReturnValueBlock) (NSString *strValue);

@interface NextViewController : UIViewController
/**
 *  声明一个ReturnValueBlock属性，这个Block是获取传值的界面传进来的
 */
@property(nonatomic, copy) ReturnValueBlock returnValueBlock;

@end

=================================================================

//.m 文件

#import "NextViewController.h"

@interface NextViewController ()

@property (weak, nonatomic) IBOutlet UITextField *inputText;

- (IBAction)back:(id)sender;

@end

@implementation NextViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.navigationItem.title = @"第二个界面";
}


/**
 *  返回上一个界面
 *
 *  @param sender 按钮
 */
- (IBAction)back:(id)sender {

    NSString *inputString = self.inputText.text;

    __weak typeof(self) weakself = self;

    if (weakself.returnValueBlock) {
        //将自己的值传出去，完成传值
        weakself.returnValueBlock(inputString);
    }

    [self.navigationController popViewControllerAnimated:YES];
    
}

@end

//.m 文件

#import "ViewController.h"
#import "NextViewController.h"

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UILabel *nextPassedValue;

- (IBAction)next:(id)sender;

@end

@implementation ViewController

- (void)viewDidLoad {
    
    [super viewDidLoad];
    
}

//点击按钮跳转到第二个界面
- (IBAction)next:(id)sender {

    NextViewController *nvc = [[NextViewController alloc]init];
    
    //赋值Block，并将捕获的值赋值给UILabel
    nvc.returnValueBlock = ^(NSString *passedValue){
        
        self.nextPassedValue.text = passedValue;
    
    };
    
    [self.navigationController pushViewController:nvc animated:YES];
 
}
@end