MVVM

public class NumModel {
    private int num = 0;

    public void add(ModelCallback callback) {
        callback.onSuccess(++num);//通知Presenter结果
    }

    public interface ModelCallback {//数据回调接口
        void onSuccess(int num);

        void onFailed(String text);
    }

}

public class VmActivity extends Activity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        NumViewModel numViewModel = new NumViewModel();
        VmActivityBinding binding = DataBindingUtil.setContentView(this, R.layout.vm_activity);
        binding.setNumVM(numViewModel);//View与ViewModel绑定
    }
}

public class NumViewModel extends BaseObservable {
    private String num;

    private final NumModel mNumModel;

    public NumViewModel() {
        mNumModel = new NumModel();
    }

    @Bindable
    public String getNum() {
        return num;
    }

    public void setNum(String num) {
        this.num = num;
        notifyPropertyChanged(BR.num);//更新UI
    }

    public void onClickAdd(View view) {//点击事件处理
        mNumModel.add(new NumModel.ModelCallback() {//相关逻辑处理，这里直接交给Model层
            @Override
            public void onSuccess(int num) {
                setNum(num + "");//成功，更新数据
            }

            @Override
            public void onFailed(String text) {
                setNum(text);//失败，更新数据
            }
        });
    }
}

// 数据模型：用户信息
public class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    // getter
    public String getUsername() { return username; }
    public String getPassword() { return password; }
}

// 业务逻辑：登录处理（Model 核心）
public class LoginModel {
    // 模拟登录验证（网络请求/数据库查询）
    public void login(User user, LoginCallback callback) {
        new Thread(() -> { // 异步操作
            try {
                Thread.sleep(1000); // 模拟网络延迟
                // 验证逻辑：用户名密码为 admin/123456
                if ("admin".equals(user.getUsername()) && "123456".equals(user.getPassword())) {
                    callback.onSuccess("登录成功");
                } else {
                    callback.onFailure("用户名或密码错误");
                }
            } catch (InterruptedException e) {
                callback.onFailure("网络异常");
            }
        }).start();
    }

    // 回调接口：通知 Presenter 处理结果
    public interface LoginCallback {
        void onSuccess(String message);
        void onFailure(String error);
    }
}

// View 接口：定义 View 需实现的功能（更新 UI、展示加载等）
public interface LoginView {
    // 显示加载中
    void showLoading();
    // 隐藏加载中
    void hideLoading();
    // 显示登录结果
    void showResult(String message);
    // 获取用户输入的用户名
    String getUsername();
    // 获取用户输入的密码
    String getPassword();
}

// View 实现类：Activity（仅处理 UI 逻辑）
public class LoginActivity extends AppCompatActivity implements LoginView {
    private EditText etUsername;
    private EditText etPassword;
    private Button btnLogin;
    private ProgressBar progressBar;
    private TextView tvResult;
    private LoginPresenter presenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        initView();
        // 初始化 Presenter（传入 View 接口）
        presenter = new LoginPresenter(this, new LoginModel());
        // 绑定登录按钮点击事件
        btnLogin.setOnClickListener(v -> presenter.login());
    }

    private void initView() {
        etUsername = findViewById(R.id.et_username);
        etPassword = findViewById(R.id.et_password);
        btnLogin = findViewById(R.id.btn_login);
        progressBar = findViewById(R.id.progress_bar);
        tvResult = findViewById(R.id.tv_result);
    }

    // 实现 LoginView 接口方法
    @Override
    public void showLoading() {
        progressBar.setVisibility(View.VISIBLE);
    }

    @Override
    public void hideLoading() {
        progressBar.setVisibility(View.GONE);
    }

    @Override
    public void showResult(String message) {
        tvResult.setText(message);
    }

    @Override
    public String getUsername() {
        return etUsername.getText().toString();
    }

    @Override
    public String getPassword() {
        return etPassword.getText().toString();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // 解除 Presenter 与 View 的关联（避免内存泄漏）
        presenter.detachView();
    }
}

public class LoginPresenter {
    // 持有 View 接口（弱引用避免内存泄漏）
    private WeakReference<LoginView> viewRef;
    // 持有 Model 实例
    private LoginModel model;

    // 构造函数：注入 View 和 Model
    public LoginPresenter(LoginView view, LoginModel model) {
        this.viewRef = new WeakReference<>(view);
        this.model = model;
    }

    // 处理登录逻辑
    public void login() {
        LoginView view = viewRef.get();
        if (view == null) return; // View 已销毁，直接返回

        // 1. 显示加载
        view.showLoading();

        // 2. 获取 View 中的用户输入
        String username = view.getUsername();
        String password = view.getPassword();
        User user = new User(username, password);

        // 3. 调用 Model 处理登录
        model.login(user, new LoginModel.LoginCallback() {
            @Override
            public void onSuccess(String message) {
                // 切换到主线程更新 UI
                if (viewRef.get() != null) {
                    viewRef.get().hideLoading();
                    viewRef.get().showResult(message);
                }
            }

            @Override
            public void onFailure(String error) {
                if (viewRef.get() != null) {
                    viewRef.get().hideLoading();
                    viewRef.get().showResult(error);
                }
            }
        });
    }

    // 解除 View 关联（Activity 销毁时调用）
    public void detachView() {
        if (viewRef != null) {
            viewRef.clear();
            viewRef = null;
        }
    }
}

// 数据模型：用户信息
public class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    // getter
    public String getUsername() { return username; }
    public String getPassword() { return password; }
}

// 登录仓库（处理数据请求）
public class LoginRepository {
    // 模拟网络登录
    public void login(User user, LoginCallback callback) {
        new Thread(() -> { // 异步操作
            try {
                Thread.sleep(1000); // 模拟网络延迟
                if ("admin".equals(user.getUsername()) && "123456".equals(user.getPassword())) {
                    callback.onSuccess("登录成功");
                } else {
                    callback.onFailure("用户名或密码错误");
                }
            } catch (InterruptedException e) {
                callback.onFailure("网络异常");
            }
        }).start();
    }

    public interface LoginCallback {
        void onSuccess(String message);
        void onFailure(String error);
    }
}

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class LoginViewModel extends ViewModel {
    // 私有可变数据（仅内部更新）
    private final MutableLiveData<Boolean> _isLoading = new MutableLiveData<>(false);
    private final MutableLiveData<String> _resultMessage = new MutableLiveData<>("");
    private final MutableLiveData<String> _username = new MutableLiveData<>("");
    private final MutableLiveData<String> _password = new MutableLiveData<>("");

    // 暴露不可变的 LiveData 给 View 观察（外部只能观察，不能修改）
    public LiveData<Boolean> isLoading = _isLoading;
    public LiveData<String> resultMessage = _resultMessage;
    public LiveData<String> username = _username;
    public LiveData<String> password = _password;

    private final LoginRepository repository;

    public LoginViewModel() {
        this.repository = new LoginRepository();
    }

    // 处理登录逻辑（供 View 调用）
    public void login() {
        String username = _username.getValue() != null ? _username.getValue() : "";
        String password = _password.getValue() != null ? _password.getValue() : "";

        // 显示加载状态
        _isLoading.setValue(true);
        _resultMessage.setValue("");

        // 调用仓库登录
        repository.login(new User(username, password), new LoginRepository.LoginCallback() {
            @Override
            public void onSuccess(String message) {
                // 切换到主线程更新数据（LiveData.postValue() 自动处理线程）
                _isLoading.postValue(false);
                _resultMessage.postValue(message);
            }

            @Override
            public void onFailure(String error) {
                _isLoading.postValue(false);
                _resultMessage.postValue(error);
            }
        });
    }

    // 更新用户名（供 View 绑定）
    public void setUsername(String username) {
        _username.setValue(username);
    }

    // 更新密码（供 View 绑定）
    public void setPassword(String password) {
        _password.setValue(password);
    }
}

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import com.example.mvvm.databinding.ActivityLoginBinding;

public class LoginActivity extends AppCompatActivity {
    private LoginViewModel viewModel;
    private ActivityLoginBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // 初始化 DataBinding
        binding = DataBindingUtil.setContentView(this, R.layout.activity_login);
        // 初始化 ViewModel
        viewModel = new ViewModelProvider(this).get(LoginViewModel.class);

        // 绑定生命周期所有者（使 LiveData 感知 Activity 生命周期）
        binding.setLifecycleOwner(this);
        // 绑定 ViewModel 到布局
        binding.setViewModel(viewModel);
        // 绑定 Activity 自身（供布局调用 login 方法）
        binding.setActivity(this);
    }

    // 登录按钮点击事件（供布局调用）
    public void login() {
        viewModel.login();
    }
}