iOS利用Block逆向传值的方式详解

//.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;

  if (self.returnValueBlock) {
    //将自己的值传出去，完成传值
    self.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