SQLite无法从android片段插入数据

Question

我试图通过SQLite从片段中保存数据，但我不能。 实际上，save和read方法运行良好，但如果片段被更改并重新加载，那么任何数据都不存在。

这是我的代码。

DB

public class ToDoItemsDB {

private static final String dbName = "ToDoItemsDB.db";
private static final String tableName = "todo_items";

private DBHelper dbHelper;
private SQLiteDatabase db;
private Context context;

public ToDoItemsDB(Context context) {
    this.context = context;
    this.dbHelper = new DBHelper(context, null, null, 1);
    db = dbHelper.getWritableDatabase();
}

public void getAllItems() {
    String sql = "select * from " + tableName;
    Cursor cursor = db.rawQuery(sql, null);
    while(cursor.moveToNext()) {
        System.out.println("result");
        System.out.println(cursor.getInt(1));
    }

    cursor.close();
}


public void addItems(int categoryID, String itemName, int itemID, String subItemName, int subItemID) {
    String sql = "insert into "
            + tableName
            + " values("
            + null
            + ","
            + categoryID
            + "," + "'"
            + itemName + "'"
            + ","
            + itemID
            + "," + "'"
            + subItemName + "'" 
            + ","
            + subItemID
            +")";
    db.execSQL(sql);
}

private class DBHelper extends SQLiteOpenHelper {

    public DBHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "create table "
                + tableName
                + "(_id integer primary key autoincrement,"
                + "category_id integer,"
                + "item_name text,"
                + "item_id integer,"
                + "sub_item_name text,"
                + "sub_item_id integer"
                + ")";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exist " + tableName);
        onCreate(db);
    }

}

MainActivity

public class MainActivity extends Activity
    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

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

    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    Fragment fragment;
    FragmentManager fragmentManager = getFragmentManager();
    switch(position) {
    case 0:
        fragment = new ToDoMainActivity();
        break;

    case 1:
        fragment = new SettingActivity();
        break;
    default:
        fragment = new ToDoMainActivity();
    }

    fragmentManager.beginTransaction()
    .replace(R.id.container, fragment)
    .commit();
}

public void onSectionAttached(int number) {
    switch (number) {
        case 1:
            mTitle = getString(R.string.title_section1);
            break;
        case 2:
            mTitle = getString(R.string.title_section2);
            break;
    }
}

public void restoreActionBar() {
    ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setTitle(mTitle);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.to_do_main, menu);
        restoreActionBar();
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_to_do_main, container, false);
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MainActivity) activity).onSectionAttached(
                getArguments().getInt(ARG_SECTION_NUMBER));
    }
}

ToDoMainActivity

public class ToDoMainActivity extends Fragment implements OnClickListener {
    private Context context;
    private ToDoItemsDB DB;
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.activity_to_do_main, container, false);
        Button btn = (Button)view.findViewById(R.id.addCategory);
        Button getBtn = (Button)view.findViewById(R.id.getAllItem);
        btn.setOnClickListener(this);
        getBtn.setOnClickListener(this);
        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        System.out.println("Acitivity Created");
        context = getActivity();
    }

    @Override
    public void onResume() {
        super.onResume();
        System.out.println("On Resume");
        DB = new ToDoItemsDB(context);
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
        case R.id.addCategory:
            Toast.makeText(context, "SET", Toast.LENGTH_SHORT).show();

            DB.addItems(3, "test", 3, null, 3);
            break;

        case R.id.getAllItem:
            Toast.makeText(context, "GET", Toast.LENGTH_SHORT).show();
            DB.getAllItems();
            break;
        }
    }
}