现在的工作中在使用MVVM（学习中），今天突然意识到之前对MVC理解错了。

现在的理解

应用就是与用户操作，处理一系列的数据后再呈现给用户。
model是处理这些数据用的，比如请求、映射、过滤、排序……
view是用来显示数据、与用户交互的。
controller是用来协调V与M的。

比如，举个例子，下面是部分代码。具体的请移步这里

Model.h

#import <Foundation/Foundation.h>

@interface Model : NSObject

@property (nonatomic, strong) NSArray *personArray;

- (void)fetchPersonArray;

@end

Model.m

#import "Model.h"
#import "Person.h"

@implementation Model

- (void)fetchPersonArray {
    // 请求网络
    // 或者
    // 访问数据库

    Person *person1 = [Person personWithName:@"aaaaa" age:1];
    Person *person2 = [Person personWithName:@"bbbbb" age:2];
    Person *person3 = [Person personWithName:@"ccccc" age:3];
    Person *person4 = [Person personWithName:@"ddddd" age:4];

    self.personArray = @[person1, person2, person3, person4];
}

@end

Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger age;

+ (instancetype)personWithName:(NSString *)name age:(NSInteger)age;

@end

ViewController.m

#import "ViewController.h"
#import "Model.h"
#import "Person.h"
#import "View.h"

@interface ViewController ()

@property (nonatomic, strong) Model *model;
@property (nonatomic, strong) View *customView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.model = [[Model alloc] init];
    [self.model addObserver:self forKeyPath:@"personArray" options:NSKeyValueObservingOptionNew context:nil];

    self.customView = [[View alloc] init];
    self.customView.frame = self.view.bounds;
    [self.view addSubview:self.customView];

    [self.model fetchPersonArray];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"personArray"]) {
        [self updateUI];
    }
}

- (void)updateUI {
    self.customView.personName1.text = [self.model.personArray[0] name];
    self.customView.personName2.text = [self.model.personArray[1] name];
    self.customView.personName3.text = [self.model.personArray[2] name];
    self.customView.personName4.text = [self.model.personArray[3] name];
}

@end

当然以上的理解还不敢说正确，但是可以肯定的是我之前是错了。
感觉挺惭愧的，错了这么久，谨记！！！

之前的理解（错误）

model是数据模型，比如上面中Person的角色
view是用来显示数据、与用户交互的。
controller是用来处理逻辑，协调V与M的。

将上面的例子用错误的方式实现如下，具体代码请移步这里

Model.h

#import <Foundation/Foundation.h>

@interface Model : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger age;

+ (instancetype)personWithName:(NSString *)name age:(NSInteger)age;

@end

ViewController.m

#import "ViewController.h"
#import "Model.h"
#import "View.h"

@interface ViewController ()

@property (nonatomic, strong) NSArray *personArray;
@property (nonatomic, strong) View *customView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.customView = [[View alloc] init];
    self.customView.frame = self.view.bounds;
    [self.view addSubview:self.customView];

    __weak ViewController *weakSelf = self;
    [self fetchPersonArray:^{
        [weakSelf updateUI];
    }];
}

- (void)fetchPersonArray:(void (^)(void))completion {
    Model *person1 = [Model personWithName:@"aaaaa" age:1];
    Model *person2 = [Model personWithName:@"bbbbb" age:2];
    Model *person3 = [Model personWithName:@"ccccc" age:3];
    Model *person4 = [Model personWithName:@"ddddd" age:4];

    self.personArray = @[person1, person2, person3, person4];

    if (completion) {
        completion();
    }
}

- (void)updateUI {
    self.customView.personName1.text = [self.personArray[0] name];
    self.customView.personName2.text = [self.personArray[1] name];
    self.customView.personName3.text = [self.personArray[2] name];
    self.customView.personName4.text = [self.personArray[3] name];
}

@end