用java代码举例MVP和MVVM的具体区别

以下是使用 Java 代码举例 MVP 和 MVVM 的具体区别：

MVP 示例代码：

Model.java:

public class Model {
    private String data;

    public void setData(String data) {
        this.data = data;
    }

    public String getData() {
        return data;
    }
}

View.java:

public interface View {
    void showData(String data);
}

public class MainActivity implements View {
    private Presenter presenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        presenter = new Presenter(this);
        presenter.loadData();
    }

    @Override
    public void showData(String data) {
        // 在视图中显示数据
        textView.setText(data);
    }
}

Presenter.java:

public class Presenter {
    private Model model;
    private View view;

    public Presenter(View view) {
        this.view = view;
        this.model = new Model();
    }

    public void loadData() {
        // 从模型获取数据
        String data = model.getData();
        // 通过视图显示数据
        view.showData(data);
    }
}

MVVM 示例代码：

Model.java:

public class Model {
    private MutableLiveData<String> data;

    public LiveData<String> getData() {
        if (data == null) {
            data = new MutableLiveData<>();
            // 模拟异步获取数据
            fetchData();
        }
        return data;
    }

    private void fetchData() {
        // 异步获取数据
        // ...
        // 数据获取成功后更新 LiveData
        data.setValue("Hello MVVM");
    }
}

ViewModel.java:

public class ViewModel extends AndroidViewModel {
    private Model model;

    public ViewModel(Application application) {
        super(application);
        model = new Model();
    }

    public LiveData<String> getData() {
        return model.getData();
    }
}

View.java:

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private ViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        textView = findViewById(R.id.text_view);
        
        viewModel = new ViewModelProvider(this).get(ViewModel.class);
        viewModel.getData().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String data) {
                // 在视图中显示数据
                textView.setText(data);
            }
        });
    }
}

在 MVP 中，Presenter 负责协调 Model 和 View，通过接口将 View 注入到 Presenter 中，Presenter 通过调用 View 的方法来更新视图。而在 MVVM 中，ViewModel 负责协调 Model 和 View，ViewModel 使用 LiveData 来观察数据的变化，一旦数据发生变化，ViewModel 就会通知 View 更新视图。这样，View 不再直接与 Model 交互，而是通过 ViewModel 来获取和展示数据。