无法将数据插入片段内的数据库

Question

I'm using fragment to create tabs, and I'm trying to insert information from the fragment to my database.

So I've 3 RadioGroup and I'm adding to the database the 'Checked' radio button that the user has marked, and I'm not able to add into the database the data because the following error:

Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference

There are DatabaseHandler functions (which works) that I use such as

db.checkSetting() - Check if the database table is empty, if empty return false, if not return true.

db.updateSetting() - Update the data inside the table.

db.addSetting() - Create new table with new data.

public class DatabaseHandler extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "database.db";

    //table name
    private static final String TABLE_DETAILS = "details";
    private static final String TABLE_FOOD = "food";
    private static final String TABLE_OLDDETAILS = "oldDetails";
    private static final String TABLE_SETTING = "setting";

    //Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_HEIGHT = "height";
    private static final String KEY_WEIGHT = "weight";
    private static final String KEY_CALORIES = "calories";
    private static final String KEY_DATE = "date";
    private static final String KEY_LEVEL = "level";
    private static final String KEY_DURATION = "duration";
    private static final String KEY_DAYS = "days";


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

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_DETAILS_TABLE = "CREATE TABLE " + TABLE_DETAILS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," +  KEY_HEIGHT + " REAL," + KEY_WEIGHT + " REAL " + ")";
        String CREATE_FOOD_TABLE = "CREATE TABLE " + TABLE_FOOD + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," + KEY_CALORIES + " INTEGER " + ")";
        String CREATE_OLDDETAILS_TABLE = "CREATE TABLE " + TABLE_OLDDETAILS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_DATE + " TEXT," +  KEY_HEIGHT + " REAL," + KEY_WEIGHT + " REAL " + ")";
        String CREATE_SETTING_TABLE = "CREATE TABLE " + TABLE_SETTING + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_LEVEL + " INTEGER," +  KEY_DURATION + " INTEGER," + KEY_DAYS + " INTEGER " + ")";

        db.execSQL(CREATE_OLDDETAILS_TABLE);
        db.execSQL(CREATE_DETAILS_TABLE);
        db.execSQL(CREATE_FOOD_TABLE);
        db.execSQL(CREATE_SETTING_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_DETAILS);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_OLDDETAILS);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_FOOD);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_SETTING);

        // Create tables again
        onCreate(db);
    }
public boolean addSetting(int level, int duration, int days) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_ID, 1);
        values.put(KEY_LEVEL, level);
        values.put(KEY_DURATION, duration);
        values.put(KEY_DAYS, days);

        // Inserting Row
        long result = db.insert(TABLE_SETTING, null, values);
        if(result == -1){
            return false;
        }
        else{
            return true;
        }
    }
   public boolean checkSetting(){
        SQLiteDatabase db = this.getWritableDatabase();
        String selectQuery = "SELECT  * FROM " + TABLE_SETTING;
        Cursor cursor = db.rawQuery(selectQuery, null);
        Boolean rowExists;

        if (cursor.moveToFirst())
        {
            // DO SOMETHING WITH CURSOR
            rowExists = true;

        } else
        {
            // I AM EMPTY
            rowExists = false;
        }
        return rowExists;
    }
    public setting getSetting() {
        String selectQuery = "SELECT  * FROM " + TABLE_SETTING;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        if (cursor != null)
            cursor.moveToFirst();
        setting set = new setting(cursor.getInt(1), cursor.getInt(2), cursor.getInt(3));

        return set;
    }
   public int updateSetting(setting set) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(KEY_LEVEL, set.getLevel());
        values.put(KEY_DURATION, set.getDuration());
        values.put(KEY_DAYS, set.getDays());
        Log.d("UPDATE: ", "updated all");

        // updating row
        return db.update(TABLE_SETTING, values, KEY_ID + " = ?", new String[] { String.valueOf(1) });
    }

Fragment:

public class PageFragment extends Fragment {
    DatabaseHandler db = new DatabaseHandler(getActivity()); //DATABASE
    private int group1;
    private int group2;
    private int group3;
    public static final String ARG_PAGE = "ARG_PAGE";

    private int mPage;

    public static PageFragment newInstance(int page) {
        Bundle args = new Bundle();
        args.putInt(ARG_PAGE, page);
        PageFragment fragment = new PageFragment();
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPage = getArguments().getInt(ARG_PAGE);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_training, container, false);
        ViewStub stub = (ViewStub) view.findViewById(R.id.stub);
        if(mPage == 1) { // mPage represents the ID of the tab/page/fragment that in use.
            stub.setLayoutResource(R.layout.fragment_trainingone); // Sets resource for each fragment
            View inflated = stub.inflate();
            return inflated;
        }
        else{
            stub.setLayoutResource(R.layout.fragment_trainingtwo);
            View inflated = stub.inflate();
            RadioGroup rg1 = (RadioGroup) inflated.findViewById(R.id.group1);
            RadioGroup rg2 = (RadioGroup) inflated.findViewById(R.id.group2);
            RadioGroup rg3 = (RadioGroup) inflated.findViewById(R.id.group3);
            Button update = (Button) inflated.findViewById(R.id.update);
            rg1.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
            {
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    switch(checkedId){
                        case R.id.radio1:
                            group1 = 1;
                            break;
                        case R.id.radio2:
                            group1 = 2;
                            break;
                        case R.id.radio3:
                            group1 = 3;
                            break;
                    }
                }
            });
            rg2.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
            {
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    switch(checkedId){
                        case R.id.radio11:
                            group2 = 1;
                            break;
                        case R.id.radio22:
                            group2 = 2;
                            break;
                        case R.id.radio33:
                            group2 = 3;
                            break;
                    }
                }
            });
            rg3.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
            {
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    switch(checkedId){
                        case R.id.radio111:
                            group3 = 1;
                            break;
                        case R.id.radio222:
                            group3 = 2;
                            break;
                        case R.id.radio333:
                            group3 = 3;
                            break;
                    }
                }
            });
            update.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(android.view.View v) {
                    setting set = new setting(group1, group2, group3);
                    if (db.checkSetting()) {
                        db.updateSetting(set);
                    } else {
                        db.addSetting(group1, group2, group3);
                    }
                }
            });
            return inflated;
        }
    }
}

How can I insert data into database within fragment and avoiding NullPointerException?

Answer 1

You're calling

DatabaseHandler db = new DatabaseHandler(getActivity());

before the Activity is even attached to the Fragment. Initialise it in the onCreate() , or onAttach() method, so getActivity() doesn't return null.

Answer 2

Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference

According to Exception You Have to open database before querying from it follow the below linked post

public void openDataBase() throws SQLException
    {
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);  
    }

SQLite database status on app uninstall