ReactiveCocoa初探

前一段项目中用到了ReactiveCocoa.今天做一下简单的总结,当然项目还在不断尝试ReactiveCocoa的最佳实践,希望自己还会有后续的文章 :)

MVC

一切要从我们熟悉的MVC架构开始,这个被戏称为Massive View Controller(臃肿的视图控制器)的软件架构如下:

MVC架构

• Model:Encapsulate the data specific to an application and define the logic and computation that manipulate and process that data.
• View:Is an object in an application that users can see.
• Controller: Acts as an intermediary between one or more of an application’s view objects and one or more of its model objects.
  From:Cocoa Core Competencies

简单来说Model用于程序的基本数据对象,View用于UI控件展示,Controller用于粘合View和Model,将Model里的数据内容展示到UI上.
CS193p上有幅图来表示MVC之间的关系及如何来进行通讯:

MVC

• Model层无法与View层进行通信的.
• Controller能直接读写调用Model,Model通过Notification&KVO来和Controller进行通信
• Controller可以直接和View层通信,通过outlet控制View上的控件,View可以通过action来射向Controller里的target来告诉Controller View中某个控件被点击等的操作.Controller还可以通过Protocol(delegate,datasource等)来对View进行控制.

MVC在iOS开发中被广泛应用,然而慢慢你会发现他有些弊端,那就是大量的处理逻辑都塞进了ViewController里面，会使其代码行数变得不可控,于是就有人引入了MVVM.

MVVM

引用ReactiveCocoa and MVVM,an Introduction中的一幅图来说明MVVM与MVC之间的联系:

MVVM & MVC

简单来说ViewModel是将Controller里面的逻辑代码分离出来,使Controller只用于将处理好的数据与View对应起来.这就会产生一个问题:ViewModel如何与Controller进行通信呢？想到的最简单的就是delegate.然而笨重写法会使代码变得难看,而拯救我们的super man就是ReactiveCocoa.

ReactiveCocoa的简单使用

• 对值的监听

    [self.usernameTextField.rac_textSignal subscribeNext:^(id x) {
        NSLog(@"username = %@", x);
    }];

• 对值的过滤

    [[self.usernameTextField.rac_textSignal
      filter:^BOOL(NSString *text) {
          return text.length > 5;
    }]
     subscribeNext:^(id x) {
         NSLog(@"filter x = %@", x);
    }];

• 对值的处理转换

    [[[self.usernameTextField.rac_textSignal map:^id(NSString *text) {
        return @(text.length);
    }]
     filter:^BOOL(NSNumber *length) {
         return [length integerValue] > 5;
     }]
     subscribeNext:^(id x) {
         NSLog(@"username x = %@", x);
     }];
 
 RACSignal *validUsernameSignal = [self.usernameTextField.rac_textSignal
                                      map:^id(NSString *text) {
                                          return @([self isValidUsername:text]);
                                      }];
  - (BOOL)isValidUsername:(NSString *)username {
         return username.length > 5;
    }

• 对值的监听

    RAC(self.passwordTextfield, backgroundColor) = [validPasswordSignal map:^id(NSNumber *passwordValid) {
        return [passwordValid boolValue] ? [UIColor clearColor] : [UIColor yellowColor];
    }];

• 信号的融合

    RACSignal *validUsernameSignal = [self.usernameTextField.rac_textSignal
                                      map:^id(NSString *text) {
                                          return @([self isValidUsername:text]);
                                      }];
    
    RACSignal *validPasswordSignal = [self.passwordTextfield.rac_textSignal
                                      map:^id(NSString *text) {
                                          return @([self isValidPassword:text]);
                                      }];
    RACSignal *signUpActiveSignal = [RACSignal combineLatest:@[validUsernameSignal,  validPasswordSignal]
                                                      reduce:^id(NSNumber *usernameValid, NSNumber *passwordValid){
                                                          return @([usernameValid boolValue] && [passwordValid boolValue]);
                                                      }];
    
    [signUpActiveSignal subscribeNext:^(NSNumber *signupActive) {
        self.loginButton.enabled = [signupActive boolValue];
    }];

• 对事件的监听

    [[[self.loginButton rac_signalForControlEvents:UIControlEventTouchUpInside]
     map:^id(id value) {
         return [self loginSignal];
     }]
     subscribeNext:^(id x) {
         NSLog(@"login result: %@", x);
     }];
- (RACSignal *)loginSignal {
    return [RACSignal createSignal:^RACDisposable *(id subscriber) {
        [self.loginService loginWithUsername:self.usernameTextField.text password:self.passwordTextfield.text complete:^(BOOL success) {
            [subscriber sendNext:@(success)];
            [subscriber sendCompleted];
        }];
        return nil;
    }];
}

Demo地址

参考

• ReactiveCocoa and MVVM,an Introduction 中文版
• Introduction to MVVM
• ReactiveCocoa Tutorial