中介者模式

基本理解

• 中介者模式又叫做调停者模式，其实就是中间人或者调停者的意思。
  
• 尽管将一个系统分割成许多对象通常可以增加可复用性，但是对象之间的连接又降低了可复用性。
  
• 如果两个类不必彼此直接通信，那么着两个类就不应当发生直接的相互作用。如果其中一个类需要调用另一个类的方法的话，可以用过第三者转发这个调用。而这个第三者就是中介者。
  
• 概念：中介者模式（Mediator）,用一个中介者对象来封装一系列的对象交互。中介者使各个对象不需要显式地相互引用，从而使其耦合松散，而且可 以独立地改变他们之间的交互。
  
• UINavigationViewController就是属于一个中介者。

中介者模式的优缺点

中介者模式很容易在系统中应用，也很容易在系统中误用。当系统出现了多对多交互复杂的对象群时，不要急于使用中介者模式，而要先反思你在系统上设计是否合理。
优点就是集中控制，减少了对象之间的耦合度。缺点就是太过于集中。

应用场景

• 对象间的交互虽定义明确然而非常复杂，导致一组对象彼此相互依赖而且难以理解。
  
• 因为对象引用了许多其他对象并与其通信，导致对象难以复用。
  
• 想要定制一个分布在多个类中的逻辑或者行为，又不想生成太多子类。

例子

CoordinatingViewController.h

//
//  CoordinatingViewController.h
//  CoordinateDemo
//
//  Created by zhanggui on 15/8/6.
//  Copyright (c) 2015年 zhanggui. All rights reserved.
//

#import <UIKit/UIKit.h>
typedef NS_ENUM(NSInteger,ButtonTag) {
    kButtontagOpenThree,
    kButtontagOpenThreeNext,
    kButtontagBackThree
};
@interface CoordinatingViewController : UIViewController


@PRoperty(nonatomic,strong)NSMutableArray *controllersArray;

@property(nonatomic,strong)UIViewController *activeController;

@property(nonatomic,strong)UIViewController *mainViewController;
+(instancetype)shareInstance;

- (void)requestViewChangeByObject:(id)sender;
@end

CoordinationgViewController.m

//
//  CoordinatingViewController.m
//  CoordinateDemo
//
//  Created by zhanggui on 15/8/6.
//  Copyright (c) 2015年 zhanggui. All rights reserved.
//

#import "CoordinatingViewController.h"
#import "ThirdViewController.h"
#import "Third2ViewController.h"

@interface CoordinatingViewController ()
{
//    UIStoryboard *storyboard;
}
@end

@implementation CoordinatingViewController

+(instancetype)shareInstance
{
    static CoordinatingViewController *coorVC;
    if (coorVC==nil) {
        coorVC = [[self alloc] init];
    }
    return coorVC;
}
- (void)viewDidLoad {
    [super viewDidLoad];
//    storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    // Do any additional setup after loading the view.
}
- (void)requestViewChangeByObject:(id)sender {
    UIStoryboard *storyboard =[UIStoryboard storyboardWithName:@"Main" bundle:nil];
    if ([sender isKindOfClass:[UIButton class]]) {
        switch ([sender tag]) {
            case kButtontagOpenThree:
            {
                ThirdViewController *thirdVC = [storyboard instantiateViewControllerWithIdentifier:@"ThirdViewController"];
                self.activeController = thirdVC;
                [self.controllersArray addObject:thirdVC];
//                UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:thirdVC];
                [self.mainViewController presentViewController:thirdVC animated:YES completion:nil];
            }
                
                break;
            case kButtontagOpenThreeNext:
            {
                Third2ViewController *third2VC = [storyboard instantiateViewControllerWithIdentifier:@"Third2ViewController"];
                [self.controllersArray addObject:third2VC];
                UIViewController *cvc = [self.controllersArray objectAtIndex:1];
                [cvc presentViewController:third2VC animated:YES completion:nil];
            }
                break;
            case kButtontagBackThree:
            {
                UIViewController *cvc = [self.controllersArray objectAtIndex:2];
                [cvc dismissViewControllerAnimated:YES completion:nil];
                [self.controllersArray removeObjectAtIndex:2];
            }
                break;
            default:
            {
                UIViewController *cvc = [self.controllersArray objectAtIndex:1];
                [cvc dismissViewControllerAnimated:YES completion:nil];
                [self.controllersArray removeObjectAtIndex:1];
            }
                break;
        }
    }
}
@end

上面这个就是中介类。
在ViewController.m

//
//  ViewController.m
//  CoordinateDemo
//
//  Created by zhanggui on 15/8/6.
//  Copyright (c) 2015年 zhanggui. All rights reserved.
//

#import "ViewController.h"
#import "CoordinatingViewController.h"

@interface ViewController ()
{
    CoordinatingViewController *coorController;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    coorController = [CoordinatingViewController shareInstance];
    coorController.controllersArray = [[NSMutableArray alloc] initWithObjects:self, nil];
    _firstButton.tag = kButtontagOpenThree;
    coorController.activeController = self;
    coorController.mainViewController = self;
    // Do any additional setup after loading the view, typically from a nib.
}


- (IBAction)showAction:(id)sender {
    [coorController requestViewChangeByObject:_firstButton];
}
@end

ThirdViewController.m

//
//  ThirdViewController.m
//  CoordinateDemo
//
//  Created by zhanggui on 15/8/6.
//  Copyright (c) 2015年 zhanggui. All rights reserved.
//

#import "ThirdViewController.h"
#import "CoordinatingViewController.h"
@interface ThirdViewController ()

@end

@implementation ThirdViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)forwardAction:(id)sender {
    if ([sender isKindOfClass:[UIButton class]]) {
        UIButton *btn = (UIButton *)sender;
        btn.tag = kButtontagOpenThreeNext;
        CoordinatingViewController *coor = [CoordinatingViewController shareInstance];
        [coor requestViewChangeByObject:btn];
    }

}
@end

Third2ViewController.m

//
//  Third2ViewController.m
//  CoordinateDemo
//
//  Created by zhanggui on 15/8/6.
//  Copyright (c) 2015年 zhanggui. All rights reserved.
//

#import "Third2ViewController.h"
#import "CoordinatingViewController.h"
@interface Third2ViewController ()

@end

@implementation Third2ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

- (IBAction)backAction:(id)sender {
    if ([sender isKindOfClass:[UIButton class]]) {
        UIButton *btn = (UIButton *)sender;
        btn.tag = kButtontagBackThree;
        CoordinatingViewController *coor = [CoordinatingViewController shareInstance];
        [coor requestViewChangeByObject:btn];
    }

}

- (IBAction)forwardAction:(id)sender {
}
@end

上面的这两个就是视图迁移的中介处理ThirdViewController和Third2ViewController。

附：

• 项目源码：http://pan.baidu.com/s/1gdGWbeV