ios代理的使用，正向传值，逆向传值

#import <UIKit/UIKit.h>
#import "SubViewController.h"
@interface ViewController : UIViewController<SubViewControllerDelegate>

@end

#import "ViewController.h"

@interface ViewController ()
{
    SubViewController *_subViewController;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    _subViewController = [[SubViewController alloc]init];

    self.view.backgroundColor = [UIColor orangeColor];
    _subViewController.delegate = self;
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(10, 30,200 , 30);
    [btn setTitle:@"跳转到SubViewController" forState:UIControlStateNormal];
    [btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];

    UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeSystem];
    btn1.frame = CGRectMake(10, 100, 200, 30);
    [btn1 setTitle:@"让SubViewController 变色" forState:UIControlStateNormal];
    [btn1 setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [btn1 addTarget:self action:@selector(btn1Click) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn1];
    // Do any additional setup after loading the view, typically from a nib.
}

-(void)btn1Click
{
    _subViewController.view.backgroundColor = [UIColor redColor];
}
-(void)btnClick
{
    [self presentViewController:_subViewController animated:YES
    completion:^{

    }];
}

-(void)changeColoer
{
    self.view.backgroundColor = [UIColor purpleColor];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

#import <UIKit/UIKit.h>

@protocol SubViewControllerDelegate <NSObject>

-(void)changeColoer;

@end

@interface SubViewController : UIViewController
@property(nonatomic,weak)__weak id<SubViewControllerDelegate>delegate;

@end

#import <UIKit/UIKit.h>

@protocol SubViewControllerDelegate <NSObject>

-(void)changeColoer;

@end

@interface SubViewController : UIViewController
@property(nonatomic,weak)__weak id<SubViewControllerDelegate>delegate;

@end

这个小demo中我建立了两个视图控制器，一个是ViewController还有一个是SubViewController

两个页面能够进行相互跳转

点击SubViewController 中的变色button能够将ViewController中的颜色改变

点击ViewController中的变色button也能够将SubView中的颜色改变

代理实质就是指针的传递