前言

MVP模式是MVC模式在Android上的一种变体，要介绍MVP就得先介绍MVC。在MVC模式中，Activity应该是属于View这一层。而实质上，它既承担了View，同时也包含一些Controller的东西在里面。这对于开发与维护来说不太友好，耦合度大高了。把Activity的View和Controller抽离出来就变成了View和Presenter，这就是MVP模式。

让我们来用mvp写一个登录界面

一、Model层

1.定义Model接口

public interface ILoginModel {
    void login(String account, String pwd, LoginListener listener);
}

2.实现ILoginModel ,用子线程睡眠3秒来模拟网络的请求过程

public class LoginModelImpl implements ILoginModel {
    private final Handler handler = new Handler(Looper.getMainLooper());

    @Override
    public void login(String account, String pwd, LoginListener listener) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(3_000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (TextUtils.equals(account, "lbj") && TextUtils.equals(pwd, "123")) {
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            listener.onSuccess();
                        }
                    });
                } else {
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            listener.onFailed();
                        }
                    });
                }
            }
        }).start();
    }
}

3.补充：Listener的定义

public interface LoginListener {
    void onSuccess();

    void onFailed();
}

二、Present 层

1.Presenter接口

代码如下（示例）：

public interface ILoginPresenter {
    void doLogin(String account,String pwd);
}

2.实现Presenter接口

public class LoginPresenterImpl implements ILoginPresenter {

    private ILoginModel model;//持有model，请求数据
    private ILoginView view;//持有view，操控界面的行为

    public LoginPresenterImpl(ILoginView loginView) {
        model = new LoginModelImpl();
        view = loginView;
    }

    @Override
    public void doLogin(String account, String pwd) {
        view.showPb();
        model.login(account, pwd, new LoginListener() {
            @Override
            public void onSuccess() {
                view.hidePb();
                view.toast("登录成功！！！");
            }

            @Override
            public void onFailed() {
                view.hidePb();
                view.toast("登录失败！！！");
            }
        });
    }
}

三、View 层

1、IView接口，抽象view的行为

public interface ILoginView {
    void showPb();//展示进度条

    void hidePb();//隐藏进度条

    void toast(String content);
}

2、Activity 去实现IView接口

public class MainActivity extends AppCompatActivity implements ILoginView {

    private EditText etAccount;
    private Button btnLogin;
    private ProgressBar pbLogin;
    private EditText etPwd;
    private LoginPresenterImpl presenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        presenter = new LoginPresenterImpl(this);
        pbLogin = findViewById(R.id.pb_login);
        btnLogin = findViewById(R.id.btn_login);
        etAccount = findViewById(R.id.et_account);
        etPwd = findViewById(R.id.et_pwd);
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                presenter.doLogin(etAccount.getText().toString(), etPwd.getText().toString());
            }
        });
    }

    @Override
    public void showPb() {
        pbLogin.setVisibility(View.VISIBLE);
    }

    @Override
    public void hidePb() {
        pbLogin.setVisibility(View.INVISIBLE);
    }

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

补充：xml

<?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=".view.MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="账号"
        android:textSize="34sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/et_account"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/textView"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="36dp"
        android:text="密码"
        android:textSize="34sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <EditText
        android:id="@+id/et_pwd"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="39dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/textView2"
        app:layout_constraintTop_toBottomOf="@+id/et_account" />

    <Button
        android:id="@+id/btn_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="59dp"
        android:text="登录"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/et_pwd" />

    <ProgressBar
        android:id="@+id/pb_login"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:visibility="invisible"
        app:layout_constraintBottom_toTopOf="@+id/btn_login"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/et_pwd" />
</androidx.constraintlayout.widget.ConstraintLayout>