Question

I’ve created a SQLite db and I want to insert a column data in a Spinner. I wrote this code below but it doesn’t work.. What is the problem?

Here is the code:

public class RemoveWorkflow2 extends Activity {

private EditText nameEditText;
private EditText classEditText;
//private EditText idEditText;
//private int mSpinnerWF;
Spinner spin;
WorkflowChoice wf = new WorkflowChoice();

MyDatabase mDB;

//MyDatabase mDB = wf.getDb();


@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.remove_wf2);

    mDB = new MyDatabase(getApplicationContext()); 
    spin = (Spinner)findViewById(R.id.wf_spinner);

    fillSpinner(spin);

    Button btn = (Button)findViewById(R.id.button11);
    btn.setText("Rimuovi");
    btn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {


        }
    });
    /*
    Spinner spin = (Spinner)findViewById(R.id.wf_spinner);
    Cursor cur = mDB.fetchWfs();
    startManagingCursor(cur);

    String[] from = new String[] { WfMetaData.WF_NAME_KEY };
    int[] to = new int[] { android.R.id.text1 };
    SimpleCursorAdapter spinAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_spinner_item, cur, from, to);
    spinAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spin.setAdapter(spinAdapter);

    spin.setOnItemSelectedListener(new OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
            Cursor c = (Cursor)parent.getItemAtPosition(pos);
            mSpinnerWF = c.getInt(c.getColumnIndexOrThrow(WfMetaData.WF_NAME_KEY));
        }
        @Override
            public void onNothingSelected(AdapterView<?> parent) {
        }
    });*/

}

private void fillSpinner(Spinner s){

    Cursor c = mDB.fetchWfs();
    startManagingCursor(c);

    // create an array to specify which fields we want to display
    String[] from = new String[]{WfMetaData.WF_NAME_KEY};
    // create an array of the display item we want to bind our data to
    int[] to = new int[]{android.R.id.text1};
    // create simple cursor adapter
    SimpleCursorAdapter adapter =
      new SimpleCursorAdapter(this, android.R.layout.simple_spinner_item, c, from, to );
    adapter.setDropDownViewResource( android.R.layout.simple_spinner_dropdown_item );
    // get reference to our spinner
    s.setAdapter(adapter);
    }

and here is the other MyDatabase:

    public class MyDatabase {  

    SQLiteDatabase mDb;
    DbHelper mDbHelper;
    Context mContext;
    private static final String DEBUG_TAG = "WFListDatabase";
    private static final String DB_NAME="WFListdb";//nome del db
    private static final int DB_VERSION=1; //numero di versione del nostro db

    public MyDatabase(Context ctx){
        mContext = ctx;
        mDbHelper = new DbHelper(ctx, DB_NAME, null, DB_VERSION);   //quando istanziamo questa classe, istanziamo anche l'helper (vedi sotto)     
    }

   public void open(){  //il database su cui agiamo è leggibile/scrivibile
            mDb=mDbHelper.getWritableDatabase();

    }

    public void close(){ //chiudiamo il database su cui agiamo
            mDb.close();
    }


    public void insertWf(String name,String cls){ //metodo per inserire i dati
            ContentValues cv=new ContentValues();
            cv.put(WfMetaData.WF_NAME_KEY, name);
            cv.put(WfMetaData.WF_CLASS_KEY, cls);
            mDb.insert(WfMetaData.WF_TABLE, null, cv);
    }



    public Cursor fetchAllWfs(){ //metodo per fare la query di tutti i dati
        return mDb.query(WfMetaData.WF_TABLE, new String[]{WfMetaData.WF_NAME_KEY, WfMetaData.WF_CLASS_KEY},null,null,null,null,null);               
    }

    static class WfMetaData {  // i metadati della tabella, accessibili ovunque
    static final String WF_TABLE = "wfs";
    static final String ID = "_id";
    static final String WF_NAME_KEY = "name";
    static final String WF_CLASS_KEY = "class";
    }


    private static final String WF_TABLE_CREATE = "CREATE TABLE IF NOT EXISTS "  //codice sql di creazione della tabella
                    + WfMetaData.WF_TABLE + " (" 
                    + WfMetaData.ID+ " integer primary key autoincrement, "
                    + WfMetaData.WF_NAME_KEY + " text not null, "
                    + WfMetaData.WF_CLASS_KEY + " text not null);";

    public Cursor fetchWfs(){ //metodo per fare la query di tutti i dati
        return mDb.query(WfMetaData.WF_TABLE, null,null,null,null,null,null);               
}

    public void delete_byName(String n){
     mDb.delete(WfMetaData.WF_TABLE, WfMetaData.WF_NAME_KEY + "='" +n + "'", null);
     //mDb.delete(WfMetaData.WF_TABLE, WfMetaData.WF_NAME_KEY + "=?", new String[] { n });

    CharSequence text = "Il Workflow "+ n +" è stato rimosso con successo!";
    int duration = Toast.LENGTH_SHORT;

    Toast toast = Toast.makeText(mContext, text, duration);
    toast.show();
    }

    private class DbHelper extends SQLiteOpenHelper { //classe che ci aiuta nella creazione del db

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

        @Override
        public void onCreate(SQLiteDatabase _db) { //solo quando il db viene creato, creiamo la tabella
            _db.execSQL(WF_TABLE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
            Log.w(DEBUG_TAG, "Upgrading database. Existing contents will be lost. ["
                    + oldVersion + "]->[" + newVersion + "]");
            _db.execSQL("DROP TABLE IF EXISTS " + WF_TABLE_CREATE);
            onCreate(_db);
        }       

    }


    public boolean isEmpty(){
        boolean isEmpty = true;
        Cursor cursor = mDb.query(WfMetaData.WF_TABLE, new String[] { WfMetaData.WF_NAME_KEY }, null, null, null, null, null);
        if (cursor != null && cursor.getCount() > 0)
        {
           isEmpty = false;
        }
        return isEmpty;
    }
}

and here is xml file:

    <?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" >

    <TextView
        android:id="@+id/textView10"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Scegli il workflow da eliminare: "
        android:gravity="center" />


    <Spinner
        android:id="@+id/wf_spinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button11"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="Button" />

</LinearLayout>

And the LoGcat with the NullPointerException..

05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1696)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1721)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread.access$1500(ActivityThread.java:124)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:968)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.os.Looper.loop(Looper.java:130)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread.main(ActivityThread.java:3844)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at java.lang.reflect.Method.invokeNative(Native Method)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at java.lang.reflect.Method.invoke(Method.java:507)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at dalvik.system.NativeStart.main(Native Method)
05-10 11:48:04.475: E/AndroidRuntime(24650): Caused by: java.lang.NullPointerException
05-10 11:48:04.475: E/AndroidRuntime(24650):    at com.tilab.wade.interactivity.android.client.RemoveWorkflow2.fillSpinner(RemoveWorkflow2.java:82)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at com.tilab.wade.interactivity.android.client.RemoveWorkflow2.onCreate(RemoveWorkflow2.java:44)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-10 11:48:04.475: E/AndroidRuntime(24650):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1660)
05-10 11:48:04.475: E/AndroidRuntime(24650):    ... 11 more
05-10 11:48:04.485: W/ActivityManager(1610):   Force finishing activity com.tilab.wade.interactivity.android.client/.RemoveWorkflow2

Answer 1

MyDatabase mDB = new MyDatabase(getApplicationContext());

you instantiate a local variable who hides the global var, so global mDB is null.

mDB = new MyDatabase(getApplicationContext());