ios代理模式-(ViewControler之间传值)

#import <UIKit/UIKit.h>

@protocol secondViewControllerDelegate <NSObject>
- (NSString *)value;
@end

@interface SecondViewController : UIViewController

@property (nonatomic,assign) id <secondViewControllerDelegate> delegate;

@end

#import "ViewController.h"
#import "SecondViewController.h"

@interface ViewController () <secondViewControllerDelegate>{
    UITextField *_textField;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //添加按钮
    UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(20, 200, 300, 40)];
    btn.backgroundColor = [UIColor grayColor];
    [btn setTitle:@"ToSecondViewController" forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(toSecondViewController) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];
    
    //添加textField
    _textField = [[UITextField alloc] initWithFrame:CGRectMake(20, 100, 300, 40)];
    _textField.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:_textField];

}
- (void)toSecondViewController {
    SecondViewController *second = [[SecondViewController alloc] init];
    //设置SecondViewController的代理为ViewController自己
    second.delegate = self;
    [self presentViewController:second animated:YES completion:nil];
}

 //实现代理方法

-(NSString *)value {
    return _textField.text;
}

@end

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    // 添加label用于显示传递的值
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(20, 100, 300, 40)];
    label.text = [_delegate value];
    label.backgroundColor = [UIColor greenColor];
    [self.view addSubview:label];
    
    //添加按钮
    UIButton *btn = [[UIButton alloc] initWithFrame:CGRectMake(20, 200, 300, 40)];
    btn.backgroundColor = [UIColor blueColor];
    [btn setTitle:@"ToViewController" forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(backFirstViewController) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];
}

- (void)backFirstViewController {
    [self dismissViewControllerAnimated:YES completion:nil];
}

@end