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iOS设计模式之中介者模式

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。

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。