iOS Block界面反向传值小demo

1、在第二个视图控制器的.h文件中定义声明Block属性：

// 定义block
@property (nonatomic, copy) void (^NextViewControllerBlock)(NSString *tfText);
@interface NextViewController ()

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

@end

- (IBAction)BtnAction:(id)sender {

    // 判断block是否为空
    if (self.NextViewControllerBlock) {

        self.NextViewControllerBlock(self.inputTF.text);
}

    [self.navigationController popViewControllerAnimated:YES];
}

2、在第一个视图中获得第二个视图控制器，并且用第二个视图控制器来调用定义的属性：

@interface AViewController ()

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

@end

- (IBAction)btnClicked:(id)sender { 

    NextViewController*nextVC = [[NextViewController alloc]init]; nextVC.NextViewControllerBlock= ^(NSString *tfText) {
    self.nextVCInfoLabel.text = tfText;
}; 

    [self.navigationController pushViewController:nextVC animated:YES];
}