iOS通过代理逆向传值的方式详解

//.h 文件

//被代理对象 做以下几件事
//1、创建一个协议，用于传值
//2、声明一个遵守上述协议的delegate属性
/**
 * 创建协议，里面有一个方法，带一个参数，该参数就是我想传出去的值
 */
@protocol passValue <NSObject>
-(void)passedValue:(NSString *)inputValue;
@end

@interface NextViewController : UIViewController
/**
 * 声明一个delegate属性
 */
@property(nonatomic, weak) id<passValue> delegate;
@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 <#sender description#>
 */
- (IBAction)back:(id)sender {
 NSString *inputString = self.inputText.text;
 //3、调用代理对象完成传值
 if(self.delegate && [self.delegate respondsToSelector:@selector(passedValue:)]){
  [self.delegate passedValue:inputString];
 }
 [self.navigationController popViewControllerAnimated:YES];
}
@end

//.h 文件

#import <UIKit/UIKit.h>
#import "NextViewController.h"
//代理对象
//实现被代理对象创建的协议，实现其中的方法，捕获传过来的值
@interface ViewController : UIViewController <passValue>
@end
=================================================================

//.m 文件
#import "ViewController.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UILabel *nextPassedValue;
- (IBAction)next:(id)sender;
@end

@implementation ViewController
- (void)viewDidLoad {
 [super viewDidLoad]; 
}

/**
 * 实现被代理对象的方法，将捕获的值设置到UILabel中
 *
 * @param inputValue 传过来的值
 */
-(void)passedValue:(NSString *)inputValue{
 self.nextPassedValue.text = inputValue;
}

//点击返回按钮跳转到第二个界面
- (IBAction)next:(id)sender { 
 NextViewController *nvc = [[NextViewController alloc]init];
 //设置被代理对象的delegate属性为代理对象即self
 nvc.delegate = self;
 [self.navigationController pushViewController:nvc animated:YES];
}
@end