使用sqlite数据填充微调器

Question

Hi I have created following code to populate spinner with list of data in column 1 of table stored in SQLite database. When I ran the program nothing appears on the spinner. I have pasted the code below. If someone could help me with the issue that would be highly appreciated.

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemSelectedListener {
    DatabaseHelper myDb;
    Spinner group;
    Spinner volt1;
    Spinner sf;
    Spinner energy;
    String group_text;
    String sf_text;
    String energy_text;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDb = new DatabaseHelper(this);

        volt1 = (Spinner) findViewById(R.id.spinner_voltage);

        List<String>names = myDb.getAllNames();
        ArrayAdapter<String> adaptervolt = new ArrayAdapter<String>(this, R.layout.spinner_layout, R.id.txt, names);
        adaptervolt.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        volt1.setAdapter(adaptervolt);
    }

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String TABLE_NAME2 = "Spark Energy Table";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public List<String> getAllNames() {
        List<String> names = new ArrayList<String>();
        SQLiteDatabase db = this.getReadableDatabase();
        String selectQuery = "SELECT * FROM"+ TABLE_NAME2;

        db.beginTransaction();
        try {
            Cursor cursor_volt = db.rawQuery(selectQuery, null);
            if (cursor_volt.moveToFirst()) { 
                do {
                    names.add(cursor_volt.getString(0));
                } while (cursor_volt.moveToNext());
                cursor_volt.close();
            }

            db.setTransactionSuccessful();
        } catch (SQLiteException e) {
            e.printStackTrace();
        } finally {
            db.endTransaction();
            db.close();
        }
        return names;
    }
}

Xml file 1:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="1">

    <TextView
        android:id="@+id/txt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

Xml file 2:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"    
    android:layout_width="match_parent"
    android:layout_height="match_parent"   
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"  
    tools:context=".MainActivity"
    android:id="@+id/id1">

    <Spinner
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:id="@+id/spinner_voltage"      
        android:layout_alignTop="@+id/textView2"
        android:layout_toRightOf="@+id/textView2"
        android:layout_toEndOf="@+id/textView2" />
</RelativeLayout>

Answer 1

you have not created your database in your helper class. first create your database inside your oncreate method of you're helper class.

you need to execute your create statement to create table and columns.

try this tutorial for help sqlite tutorial