SQLite 项目未添加到数据库

Question

我正在为我的 Android 应用设置 SQLite 数据库，并希望支持添加和删除 RecyclerView 项目。我怎样才能修复我的代码，以便添加项目？

当我添加项目时，它们会出现在 RecyclerView 中，但不会出现在 SQLite 数据库中。我知道会发生这种情况，因为当我重新启动应用程序或导航到另一个 Fragment 时，RecyclerView 变为空。我也检查了SQLite数据库文件，它是空的。

我在 YouTube 上学习了一些关于在 SQLite 中添加和删除项目的教程，但它们似乎都使用了 "ID" 系统，而我的类没有。

我试图通过 "name" 属性引用 SQLite 数据库中的每个项目，您可以在 COLUMN_NAME 中看到它。这将包含一个城市名称，它是一个字符串。

我添加到我的 RecyclerView 的项目是从 JSON 生成的 POJO。

DatabaseHelper.java

public class DatabaseHelper extends SQLiteOpenHelper {

public static final String DATABASE_NAME = "stations.db";
private static final int DATABASE_VERSION = 3;
public static final String TABLE_NAME = "Station";
public static final String COLUMN_NAME = "_name";
public static final String COLUMN_JSON = "json";


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

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(" CREATE TABLE " + TABLE_NAME + " (" +
            COLUMN_NAME + " BLOB NOT NULL, " +
            COLUMN_JSON + " BLOB NOT NULL);"
    );
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // you can implement here migration process
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
    this.onCreate(db);
}

/**
 * Returns all the data from database
 * @return
 */
public Cursor getData(){
    SQLiteDatabase db = this.getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_NAME;
    Cursor data = db.rawQuery(query, null);
    return data;
}

/**
 * create record
 **/
public void saveStationRecord(String stationJSON) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(COLUMN_JSON, stationJSON);
    db.insert(TABLE_NAME, null, values);
    db.close();
}

/**
 * delete record
 **/
public void deleteStationRecord(String name, Context context) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.execSQL("DELETE FROM " + TABLE_NAME + " WHERE _name='" + name + "'");
}

ListAdapter.java（RecyclerView 适配器）

public void removeItem(int position) {
    Station station = stationList.get(position);
    DatabaseHelper dbHelper = new DatabaseHelper(context);
    dbHelper.deleteStationRecord(station.getData().getCity(), context);
    stationList.remove(position);
    // notify item added by position
    notifyItemRemoved(position);
    //notifyItemRangeChanged(position, stationList.size());
}

ListFragment.java（显示 RecyclerView 的位置）

@Override
public void onStart() {
    super.onStart();
    //loadDataFromFirebase();
    loadDataFromSQLiteDatabase();
}

public void addData(String data) {
    databaseHelper = new DatabaseHelper(getActivity());
    databaseHelper.saveStationRecord(data);
}

private void loadDataFromSQLiteDatabase() {
    //Get the JSON data with the DatabaseHelper class
    Cursor data = databaseHelper.getData();
    //Using Gson to turn JSON to Java object of Station
    //Create new GsonBuilder and Gson objects
    GsonBuilder gsonBuilder = new GsonBuilder();
    Gson gson = gsonBuilder.create();
    while (data.moveToNext()) {
        //Get the next JSON from the database
        String jsonResponse = data.getString(1);
        //Create a new Station object and use Gson to deserialize JSON data
        //into the Station object
        Station station = gson.fromJson(jsonResponse, Station.class);
        //Add the new Station object to the ArrayList of Station objects
        //This is to create another entry in the RecyclerView
        //Tell the RecyclerView listAdapter that our data is updated
        //because Station was just to the ArrayList
        stationList.add(station);
    }
}

private void loadSelectedDataToRecyclerView(String selectedStation) {
    RequestQueue requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());
    StringRequest stringRequest = new StringRequest(Request.Method.GET, generateRequestURL(selectedStation),
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    GsonBuilder gsonBuilder = new GsonBuilder();
                    Gson gson = gsonBuilder.create();
                    Station station = gson.fromJson(response, Station.class);
                    stationList.add(station);
                    listAdapter.notifyDataSetChanged();
                    //Add the new Station object to SQLite database
                    addData(response);
                    Log.d("API RESPONSE", response);
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Log.d("VOLLEY ERROR", error.toString());
        }
    });
    requestQueue.add(stringRequest);
}

我希望添加到 RecyclerView 的项目也能添加到 SQLite 数据库，这样当我重新启动应用程序或导航到另一个 Fragment 时，该项目将保留在 RecyclerView 中。

Answer 1

我已经解决了我的问题。

再次查看我的代码后，在 saveStationRecord 中我未能指定 COLUMN_NAME。

这是更新后的代码。

public void saveStationRecord(String stationJSON) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    GsonBuilder gsonBuilder = new GsonBuilder();
    Gson gson = gsonBuilder.create();
    //Create a new Station object and use Gson to deserialize JSON data
    //into the Station object
    Station station = gson.fromJson(stationJSON, Station.class);
    values.put(COLUMN_NAME, station.getData().getCity());
    values.put(COLUMN_JSON, stationJSON);
    db.insert(TABLE_NAME, null, values);
    db.close();
}

我用 Gson 将 JSON 变回 POJO，然后我将城市名称放入 COLUMN_NAME。

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