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{
@Override
public 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{
@Override
public void showLoading() {
System.out.println("正在登录...");
}
@Override
public void hideLoading() {
System.out.println("登录完成,获取结果");
}
@Override
public void loginFail() {
System.out.println("登录失败");
}
@Override
public 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() {
@Override
public void loginFail() {
userView.hideLoading();
userView.loginFail();
}
@Override
public 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{
@Override
public 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{
@Override
public void showLoading() {
System.out.println("正在登录...");
}
@Override
public void hideLoading() {
System.out.println("登录完成,获取结果");
}
@Override
public void loginFail() {
System.out.println("登录失败");
}
@Override
public 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() {
@Override
public void loginFail() {
userView.hideLoading();
userView.loginFail();
}
@Override
public 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。