许多 ViewModel 实例，如何解决？

Question

创建了 ViewModelFactory

public class ViewModelFactory extends ViewModelProvider.NewInstanceFactory {
    @SuppressLint("StaticFieldLeak")
    private static volatile ViewModelFactory INSTANCE;

    private final Application application;

    public static ViewModelFactory getInstance(Application application) {
        if (INSTANCE == null) {
            synchronized (ViewModelFactory.class) {
                if (INSTANCE == null) {
                    INSTANCE = new ViewModelFactory(application);
                }
            }
        }
        return INSTANCE;
    }

    private ViewModelFactory(Application application) {
        this.application = application;
    }

    @Override
    public <T extends ViewModel> T create(Class<T> modelClass) {

        if (modelClass.isAssignableFrom(MyViewModel.class)) {
            //noinspection unchecked
            return (T) new MyViewModel(
                    Repository.getInstance(
                            RemoteDataSource.getInstance(WebService.getInstance().getWebServiceApi()),
                            LocalDataSource.getInstance(new AppExecutors(), MyDatabase.getInstance(application).myDao())
                    )
            );
        }

        throw new IllegalArgumentException("Unknown ViewModel class: " + modelClass.getName());
    }
}

在 Activity 中，我创建了一个 ViewModel 实例：

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

    Log.d(TAG, "onCreate");

    if (savedInstanceState == null) {
        myViewModel = ViewModelProviders.of(this, ViewModelFactory.getInstance(this.getApplication())).get(MyViewModel.class);
    }
}

然后我想在片段中使用 MyViewModel 并按照 this example:

public class Fragment1 extends Fragment {
...

    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        myViewModel = ViewModelProviders.of(this, ViewModelFactory.getInstance(getActivity().getApplication())).get(MyViewModel.class);

        ...
    }
}

和

public class Fragment2 extends Fragment {
...

    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        myViewModel = ViewModelProviders.of(this, ViewModelFactory.getInstance(getActivity().getApplication())).get(MyViewModel.class);

        ...
    }
}

问题是在创建片段时，创建了一个新的 MyViewModel 实例（我在日志中看到这个，在 MyViewModel 构造函数中，我显示 "New MyViewModel Instance Created"）。随着每个新片段的打开，我在日志中看到 "New MyViewModel Instance Created".

请帮我了解如何解决这个问题？

Answer 1

您正在使用 ViewModelProviders.of(this, ...)。这意味着您需要一个与该特定 Fragment 关联的 ViewModel 实例。

如果您希望 ViewModel 实例与 Activity 关联，您应该在片段中使用 ViewModelProviders.of(requireActivity(), ...)。

许多 ViewModel 实例，如何解决？

Many instances of ViewModel, how to fix it?

android

mvvm

viewmodel