1. 概述

MVP,即是Model,View,Presenter架构模式.看起来类似MVC,其实不然.从上图能看到Model层和View层没有相连接,完全解耦.

2. 分层

• M层:模型层(Model),此层和MVC中的M层作用类似.主要是实体类,数据库,网络等存在的层面
• V层:视图层(View),在MVC中V层只包含XML文件,而MVP中V层包含XML,Activity和Fragment三者.理论上V层不涉及任何逻辑,只负责界面的改变,尽量把逻辑处理放到M层.
• P层:通知层(Presenter),P层的主要作用就是连接V层和M层,起到一个通知传递数据的作用.

3. 原理

用户触碰界面触发事件,View层把事件通知Presenter层,Presenter层通知Model层处理这个事件,Model层处理后把结果发送到Presenter层,Presenter层再通知View层,最后View层做出改变.这是一整套流程.

4. MVP架构优缺点

• 缺点

MVP中接口过多.
每一个功能,相比于MVC要多写好几个文件.
如果某一个界面中需要请求多个服务器接口,这个界面文件中会实现很多的回调接口,导致代码繁杂.
如果更改了数据源和请求中参数,会导致更多的代码修改.
额外的代码复杂度及学习成本.

• 优点

模块职责划分明显,层次清晰,接口功能清晰.
Model层和View层分离,解耦.修改View而不影响Model.
功能复用度高,方便.一个Presenter可以复用于多个View,而不用更改Presenter的逻辑.
有利于测试驱动开发,以前的Android开发是难以进行单元测试.
如果后台接口还未写好,但已知返回数据类型的情况下,完全可以写出此接口完整的功能.

5. MVP简单案例

①.布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <EditText
        android:id="@+id/tv_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入账号"
        app:layout_constraintTop_toTopOf="parent" />
    <EditText
        android:id="@+id/tv_pass"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入密码"
        app:layout_constraintTop_toBottomOf="@id/tv_name" />

    <Button
        android:id="@+id/btn_login"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@+id/tv_pass"
        android:text="登录" />

</androidx.constraintlayout.widget.ConstraintLayout>

②. 页面

public class MainActivity extends AppCompatActivity {

    private Button btn;
    private TextView tv_item;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
        btn = (Button) findViewById(R.id.btn);
        tv_item = (TextView) findViewById(R.id.tv_item);

        btn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn:

                break;
        }
    }
}

④. Api

public interface ApiService {
    String baseUrl="https://www.wanandroid.com/user/";

    @POST("login")
    @FormUrlEncoded
    Observable<MyBean> post(@Field("username") String username, @Field("password") String password);
}

⑤. Model

public interface LoginModel {
    void login(LoginCallback loginCallback,String name,String pass);
}

public class ImpLoginModel implements LoginModel{
    @Override
    public void login(final LoginCallback loginCallback, String name, String pass) {
        final Retrofit retrofit= new Retrofit.Builder()
                .baseUrl(ApiService.baseUrl)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        ApiService apiService = retrofit.create(ApiService.class);

        Observable<MyBean> post = apiService.post(name, pass);

        post.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<MyBean>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onNext(MyBean myBean) {
                        int errorCode = myBean.getErrorCode();
                        if(errorCode==0){
                            loginCallback.onSuccess(myBean);
                        }else {
                            loginCallback.onFail(myBean.getErrorMsg());
                        }
                    }

                    @Override
                    public void onError(Throwable e) {
                        loginCallback.onFail("网络错误");
                    }

                    @Override
                    public void onComplete() {

                    }
                });
    }
}

⑥. CallBack

public interface LoginCallback  {
    void onSuccess(MyBean myBean);
    void onFail(String error);
}

⑥. Presenter

public interface LoginPresenter {
    void loge(String name,String pass);
}


public class ImpLoginPresenter implements LoginPresenter, LoginCallback {
    private LoginView loginView;
    private ImpLoginModel impLoginModel;

    public ImpLoginPresenter(LoginView loginView) {
        this.loginView = loginView;
        impLoginModel=new ImpLoginModel();
    }

    @Override
    public void loge(String name, String pass) {
        if(TextUtils.isEmpty(name)){
            loginView.onFail("输入账号");
        }
        if(TextUtils.isEmpty(pass)){
            loginView.onFail("输入密码");
        }

        impLoginModel.login(this,name,pass);

    }

    @Override
    public void onSuccess(MyBean myBean) {
        loginView.onSuccess(myBean);
    }

    @Override
    public void onFail(String error) {
        loginView.onFail(error);
    }
}

⑦. IView

public interface LoginView {
    void onSuccess(MyBean myBean);
    void onFail(String error);
}


public class MainActivity extends AppCompatActivity implements View.OnClickListener, LoginView {

    private EditText tv_name;
    private EditText tv_pass;
    private Button btn_login;
    private ImpLoginPresenter impLoginPresenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        impLoginPresenter = new ImpLoginPresenter(this);
        initView();
    }

    private void initView() {
        tv_name = (EditText) findViewById(R.id.tv_name);
        tv_pass = (EditText) findViewById(R.id.tv_pass);
        btn_login = (Button) findViewById(R.id.btn_login);

        btn_login.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_login:
                login();
                break;
        }
    }

    private void login() {
        String name = tv_name.getText().toString();
        String pass = tv_pass.getText().toString();

        impLoginPresenter.loge(name,pass);
    }



    @Override
    public void onSuccess(MyBean myBean) {
        Toast.makeText(this,"登陆成功",Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onFail(String error) {
        Toast.makeText(this,error,Toast.LENGTH_SHORT).show();
    }
}