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另一个是SubViewController

两个页面可以进行相互跳转

点击SubViewController 中的变色按钮可以将ViewController中的颜色改变

点击ViewController中的变色按钮也可以将SubView中的颜色改变

代理实质就是指针的传递