我所理解的MVVM

不确定，MVVM是不是为了解决MVC中臃肿的C，
但是，它的确完美解决掉了MVC中臃肿的C。

1. MVC
   C同时拥有M和V，作为两者之间的桥梁，注定要导致它的臃肿。

   
   mvc

2. MVVM
   单向拥有，完全解耦，自然简单、便于维护、容易理解

   
   mvvm
3. 参考文献
   巧哥的观点有点老，但是辩证的看，还是能有收获
   我对MVC的理解个人观点，欢迎讨论
   喵神翻译的一本书上面的两张图也出自这里
4. 介绍两者的文章、博客、书籍很多，这里不多说，直接上代码

介绍一下这个小需求:对，就这么简单

1. 从服务端返回User数据（包括：id(int)、name(string)、age(int)、university(string)、sex(int)）
2. 在界面上展示User数据（包括：姓名(string)、大学(string)、性别(string)）
3. 要求性别转换（1->男；2->女），大学最长显示三个字符

• User

  #import <Foundation/Foundation.h>
     
  @interface User : NSObject
     
  @property (nonatomic, assign) NSInteger identifier;
  @property (nonatomic, copy) NSString *name;
  @property (nonatomic, assign) NSInteger age;
  @property (nonatomic, copy) NSString *university;
  @property (nonatomic, assign) NSInteger sex;
     
  @end
  

  #import "User.h"
     
  @implementation User
     
  @end
  

• Model

  #import <Foundation/Foundation.h>
  #import "User.h"
  
  @interface Model : NSObject
  
  @property (nonatomic, assign, readonly, getter=isLoading) BOOL load;
  @property (nonatomic, strong, readonly) User *user;
  
  - (void)fetchUser;
  
  @end
  

  #import "Model.h"
  
  @interface Model ()
  
  @property (nonatomic, strong) User *user;
  @property (nonatomic, assign, getter=isLoading) BOOL load;
  
  @end
  
  @implementation Model
  
  - (void)fetchUser
  {
      // 模拟网络请求，或者数据库访问
      self.load = YES;
      dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
          User *user = [[User alloc] init];
          user.identifier = 1;
          user.name = @"李远超";
          user.age = 28;
          user.university = @"山东工商学院";
          user.sex = 1;
          self.load = NO;
          self.user = user;
      });
  }
  
  @end
  

• ViewModel

  #import <Foundation/Foundation.h>
  
  @interface ViewModel : NSObject
  
  @property (nonatomic, copy, readonly) NSString *name;
  @property (nonatomic, copy, readonly) NSString *university;
  @property (nonatomic, copy, readonly) NSString *sex;
  @property (nonatomic, assign, readonly, getter=isLoading) BOOL load;
  
  - (void)fetchUser;
  
  @end
  

  #import "ViewModel.h"
  #import "Model.h"
  #import <ReactiveObjC.h>
  
  @interface ViewModel ()
  
  @property (nonatomic, copy) NSString *name;
  @property (nonatomic, copy) NSString *university;
  @property (nonatomic, copy) NSString *sex;
  @property (nonatomic, assign, getter=isLoading) BOOL load;
  
  @property (nonatomic, strong) Model *model;
  
  @end
  
  @implementation ViewModel
  
  - (instancetype)init
  {
      self = [super init];
      if (self) {
          _model = [[Model alloc] init];
  
          RAC(self, name) = [[RACObserve(_model, user) skip:1] map:^id _Nullable(User *user) {
              return user.name;
          }];
          RAC(self, university) = [[RACObserve(_model, user) skip:1] map:^id _Nullable(User *user) {
              NSString *university = user.university;
              if (user.university.length > 3) {
                  university = [university substringToIndex:3];
              }
              return university;
          }];
          RAC(self, sex) = [[RACObserve(_model, user) skip:1] map:^id _Nullable(User *user) {
              return user.sex == 1 ? @"男" : @"女";
          }];
          RAC(self, load) = [RACObserve(_model, load) skip:1];
      }
      return self;
  }
  
  - (void)fetchUser
  {
      [self.model fetchUser];
  }
  
  @end
  

• ViewController

  #import <UIKit/UIKit.h>
  
  @interface ViewController : UIViewController
  
  @end
  

  #import "ViewController.h"
  #import "ViewModel.h"
  #import <ReactiveObjC.h>
  
  @interface ViewController ()
  
  @property (nonatomic, strong) ViewModel *viewModel;
  @property (weak, nonatomic) IBOutlet UILabel *nameLabel;
  @property (weak, nonatomic) IBOutlet UILabel *universityLabel;
  @property (weak, nonatomic) IBOutlet UILabel *sexLabel;
  @property (weak, nonatomic) IBOutlet UILabel *loadLabel;
  
  @end
  
  @implementation ViewController
  
  - (void)viewDidLoad {
      [super viewDidLoad];
      self.viewModel = [[ViewModel alloc] init];
  
      RAC(self.nameLabel, text) = RACObserve(self.viewModel, name);
      RAC(self.universityLabel, text) = RACObserve(self.viewModel, university);
      RAC(self.sexLabel, text) = RACObserve(self.viewModel, sex);
      RAC(self.loadLabel, text) = [RACObserve(self.viewModel, load) map:^id _Nullable(NSNumber *value) {
          return [value boolValue] ? @"loading" : @"normal";
      }];
  }
  
  - (IBAction)fetchDataAction:(UIButton *)sender
  {
      [self.viewModel fetchUser];
  }
  
  @end