Objective-C

这里演示反向传值

SecondVC.h
@protocol sendValueDelegate <NSObject>
- (void)sendValueString:(NSString *)str;
@end
@interface OC_SecController : UIViewController
@property (nonatomic,assign) id<sendValueDelegate> delegate;

SecondVC.m
// 跳转方法中
- (void)clickBack:(UIButton *)button
{
    if (self.delegate && [self.delegate respondsToSelector:@selector(sendValueString:)]) {
        // i am a String 是传过去的字符串
        [self.delegate sendValueString:@"i am a String"];
    }
    [self dismissModalViewControllerAnimated:YES];
}

RootVC.m

- (void)click:(UIButton *)button
{
    OC_SecController *sec = [[OC_SecController alloc] init];
    // 指定代理人
    sec.delegate = self;
    [self presentViewController:sec animated:YES completion:^{

    }];
}
// 实现代理方法
- (void)sendValueString:(NSString *)str
{
    // str 就是传过来的值
    NSLog(@"string : %@",str);
}

Swift

Swift 版本 我单独创建了一份协议
commond+ n

Protrol.swift
// 定义一个协议
protocol ModeViewControlDelegate{
    // 协议方法
    func changeLabelString(newString: String)

}

SecondVC.swift
var delegate : ModeViewControlDelegate?
// 跳转返回的点击事件
func click()->Void{
        let str = textField.text
        self.delegate?.changeLabelString(str!)
        self.dismissViewControllerAnimated(true) { () -> Void in

        }
    }

RootVc.swift
// 实现协议中的方法
    func changeLabelString(newString: String) {

        label.text = "labeltext:\(newString)"
        print(newString) // newString 从secondVC.swift 传过来的值
    }
    // 跳转的点击方法
    func click()->Void
    {
        print("-------")
        let sec = SecViewController();
        sec.delegate = self
        self.presentViewController(sec,animated: true) { () -> Void in

        }
    }

demo: https://github.com/Zhangjingwang1993/SwiftProtocol Swift / OC 进阶群: 498143780