如何在视图持有者中从sqlite中获取值

import android.arch.lifecycle.ViewModel;
import android.arch.lifecycle.LiveData;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "my_database";
    private static final int DATABASE_VERSION = 1;

    public MyDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // 在此处创建数据库表格
        db.execSQL("CREATE TABLE IF NOT EXISTS my_table (id INTEGER PRIMARY KEY AUTOINCREMENT, value TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 在此处更新数据库表格
        db.execSQL("DROP TABLE IF EXISTS my_table");
        onCreate(db);
    }
}

public class MyViewModel extends ViewModel {
    private LiveData<String> value;

    public LiveData<String> getValue(Context context) {
        if (value == null) {
            value = new MutableLiveData<>();
            loadValue(context);
        }
        return value;
    }

    private void loadValue(Context context) {
        MyDatabaseHelper dbHelper = new MyDatabaseHelper(context);
        SQLiteDatabase db = dbHelper.getReadableDatabase();

        Cursor cursor = db.query("my_table", new String[]{"value"}, null, null, null, null, null);
        if (cursor != null && cursor.moveToFirst()) {
            String retrievedValue = cursor.getString(cursor.getColumnIndex("value"));
            value.setValue(retrievedValue);
            cursor.close();
        }

        db.close();
    }
}

public class MyActivity extends AppCompatActivity {
    private MyViewModel viewModel;

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

        viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
        viewModel.getValue(this).observe(this, new Observer<String>() {
            @Override
            public void onChanged(String value) {
                // 在此处处理从SQLite中获取的值
            }
        });
    }
}