MVC，MVP，MVVM的理解和区别

MVC

MVC ，早期的开发架构，在安卓里，用res代表V，activity代表Controller层，Model层完成数据请求，更新操作，activity完成view的绑定，以及业务逻辑的编写，更新view，这种模式是单向的，虽然代码存在分层，但是之间的耦合性还是很高，并且C层做的事情很多，久而久之会变得臃肿。

代码实现：

ViewModel

   static class  StudentModel{private String name;private int age;public StudentModel(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

View层

    static class  StudentView{public  void PrintStudentData(String name ,int age){System.out.println("Student name:"+name+"   age:"+age);}}

Controller

static class StudentController{StudentModel model;StudentView view;public StudentController(StudentModel model, StudentView view) {this.model = model;this.view = view;}public void setStudentName(String name){model.setName(name);}public String getStudentName(){return model.getName();}public void setStudentAge(int age){model.setAge(age);}public  Integer getStudentAge(){return model.getAge();}public  void updateView(StudentView view){view.PrintStudentData(model.getName(),model.getAge());}}

完整代码

package com.example.lib;public class MvcTest {public static void main(String[] args) {StudentModel student = getStudentDataBase();StudentView view = new StudentView();StudentController controller = new StudentController(student,view);controller.updateView(view);controller.setStudentName("lisi");controller.updateView(view);}public static StudentModel getStudentDataBase(){return new StudentModel("zhangsan",18);}static class  StudentModel{private String name;private int age;public StudentModel(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}static class  StudentView{public  void PrintStudentData(String name ,int age){System.out.println("Student name:"+name+"   age:"+age);}}static class StudentController{StudentModel model;StudentView view;public StudentController(StudentModel model, StudentView view) {this.model = model;this.view = view;}public void setStudentName(String name){model.setName(name);}public String getStudentName(){return model.getName();}public void setStudentAge(int age){model.setAge(age);}public  Integer getStudentAge(){return model.getAge();}public  void updateView(StudentView view){view.PrintStudentData(model.getName(),model.getAge());}}}

MVP

于是，出现了MVP模式，这个架构模式在安卓移动端开发中比较常见，将Activity和res统一作为V层，Model层还是完成数据的请求和更新，新建了一个类Presenter，用来作为P层，这样的好处是，方便管理每一个Activity的业务逻辑，拿到数据后，通过接口回调的方式，更新View层，实现了双向通信。缺点是需要实现Presenter类，并且需要开发接口，对简单的业务逻辑比较繁琐，且P层的事情还是比较臃肿

代码实现（以登录事务为例）：

ViewModel层

相比与MVC的ViewModel,MVP的不同在于ViewModle多实现了一个IUser接口，从而实现双向通信

    interface IUser{void login(String name,String password,OnLoginListener listener);}interface OnLoginListener{void loginFail();void loginSuccess(User user);}static class UserModel implements IUser{@Overridepublic void login(String name, String password, OnLoginListener listener) {//模拟一下登录if(name.equals("admin")&&password.equals("123456")){User user = new User();user.setUsername(name);user.setPassword(password);listener.loginSuccess(user);}else{listener.loginFail();}}}

View层：

在Android开发中，MVP架构模式里，View层指的是Activity和res。同理，也实现了一个IUserLogin接口，从而和P层实现双向通信

 static class UserView implements IUserLogin{@Overridepublic void showLoading() {System.out.println("正在登录...");}@Overridepublic void hideLoading() {System.out.println("登录完成,获取结果");}@Overridepublic void loginFail() {System.out.println("登录失败");}@Overridepublic void loginSuccess(User user) {System.out.println("username:"+ user.getUsername()+" 登陆成功");}}interface IUserLogin{void showLoading();void hideLoading();void loginFail();void loginSuccess(User user);}

Presenter层

 static class UserPresenter {private final UserModel userModel;private final UserView userView;private final User user;public UserPresenter(UserView userView) {this.userModel = new UserModel();this.userView = userView;user = new User("admin","123456");}void login(){userView.showLoading();userModel.login(user.getUsername(), user.getPassword(), new OnLoginListener() {@Overridepublic void loginFail() {userView.hideLoading();userView.loginFail();}@Overridepublic void loginSuccess(User user) {userView.hideLoading();userView.loginSuccess(user);}});}}

完整代码如下：

package com.example.lib;public class MvpTest {public static void main(String[] args) {UserView loginView  = new UserView();UserPresenter presenter = new UserPresenter(loginView);presenter.login();}static class User{String username;String password;public User() {}public User(String username, String password) {this.username = username;this.password = password;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}interface IUser{void login(String name,String password,OnLoginListener listener);}interface OnLoginListener{void loginFail();void loginSuccess(User user);}static class UserModel implements IUser{@Overridepublic void login(String name, String password, OnLoginListener listener) {//模拟一下登录if(name.equals("admin")&&password.equals("123456")){User user = new User();user.setUsername(name);user.setPassword(password);listener.loginSuccess(user);}else{listener.loginFail();}}}static class UserView implements IUserLogin{@Overridepublic void showLoading() {System.out.println("正在登录...");}@Overridepublic void hideLoading() {System.out.println("登录完成,获取结果");}@Overridepublic void loginFail() {System.out.println("登录失败");}@Overridepublic void loginSuccess(User user) {System.out.println("username:"+ user.getUsername()+" 登陆成功");}}interface IUserLogin{void showLoading();void hideLoading();void loginFail();void loginSuccess(User user);}static class UserPresenter {private final UserModel userModel;private final UserView userView;private final User user;public UserPresenter(UserView userView) {this.userModel = new UserModel();this.userView = userView;user = new User("admin","123456");}void login(){userView.showLoading();userModel.login(user.getUsername(), user.getPassword(), new OnLoginListener() {@Overridepublic void loginFail() {userView.hideLoading();userView.loginFail();}@Overridepublic void loginSuccess(User user) {userView.hideLoading();userView.loginSuccess(user);}});}}}

MVVM

再后面，就是MVVM，同理，Activity和res还是作为V层，Model层请求数据和更新，出现了一个ViewModel的层，这个类的职责在于，对数据进行绑定，以数据驱动View层，同样，当视图层改变后，Model层也能更新，从而实现了M和V之间的双向绑定。最常用的是谷歌2015年推出的jetpack的组件DataBinding，无须进行view绑定，避免了空指针等很多繁琐的业务逻辑。

代码实现：略，用JetPack提供的databinding即可

总结
MVC,MVP,MVVM的出现，都是为了视图分层，使代码结构，逻辑变得清晰，同时，实现类的单一职责，降低耦合度。但是同时选用架构设计模式的时候，也要根据业务类型来考虑，避免出现大多繁琐的设计，总之，一切为了开发效率。