how to make a Listview in a Fragment extend DATA from SQLite DATABASE

hi guys I'm new to android Studio.I just show my data in listview from SQLite database, was stuck and I can not give advice on how to fill list in fragment extend records from SQLite database. Looking and I have tried many tutorials, but no not sat down or failed. The biggest problem i got is null Exception error.

here is my DailyPurchase.java code

public class DailyPurchase extends Fragment {

    private CustomersDbAdapter dbHelper;
    ListView slist;
    private SimpleCursorAdapter dataAdapter;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View view = inflater.inflate(R.layout.dialy_purchase, container, false);

        dbHelper = new CustomersDbAdapter(getActivity());
        dbHelper.open();
        displayListView();
        return view;
    }
    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private void displayListView(){
        Cursor cursor = dbHelper.queueAll();
        slist = (ListView) getActivity().findViewById(R.id.listView21);
        // The desired columns to be bound
        String[] columns = new String[] {
                CustomersDbAdapter.CASH_PURCHASE_AMOUNT,
                CustomersDbAdapter.CASH_PURCHASE_COMPANY};

        // the XML defined views which the data will be bound to
        int[] to = new int[] {
                R.id.scustomer,
                R.id.sstate};
        dataAdapter = new SimpleCursorAdapter(getActivity(), R.layout.dailypurchase_listview, cursor, columns, to,0);
        try {
            slist.setAdapter(dataAdapter);
        } catch (Exception e) {
                  e1.printStackTrace();
       }
    }  
}

Here is my CustomersDbAdapter.java code

public class CustomersDbAdapter {
public static final String TAG = "CustomersDbAdapter";
    public DatabaseHelper mDbHelper;
    public SQLiteDatabase mDb;
public static final String DIALY_PURCHASE_CASH_TABLE = "TableDailyPurchase";
    public static final String CASH_PURCHASE_COMPANY = "companyName";
    public static final String CASH_PURCHASE_AMOUNT = "cashinneramount";

    public static final String CREATE_DIALY_PURCHASE_CASH = "CREATE TABLE "+DIALY_PURCHASE_CASH_TABLE+"" +
            "("+KEY_ROWID+" INTEGER PRIMARY KEY AUTOINCREMENT," +
            ""+CASH_PURCHASE_COMPANY+" VARCHAR2(255)," +
            ""+CASH_PURCHASE_AMOUNT+" INTEGER," +
            ""+CASH_CREATED_AT+" DATETIME DEFAULT CURRENT_TIMESTAMP," +
            "UNIQUE (" + CASH_PURCHASE_COMPANY +"))";
public final Context mCtx;
public static class DatabaseHelper extends SQLiteOpenHelper {

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


        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_DIALY_PURCHASE_CASH);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS " + DIALY_PURCHASE_CASH_TABLE);
            onCreate(db);
        }
    }

    public CustomersDbAdapter(Context ctx) {
        this.mCtx = ctx;
    }

    public CustomersDbAdapter open() throws SQLException {
        mDbHelper = new DatabaseHelper(mCtx);
        mDb = mDbHelper.getWritableDatabase();
        return this;
    }
public void close() {
        if (mDbHelper != null) {
            mDbHelper.close();
        }
    }

public long dialycash(String name, int amount ){

        ContentValues initialValues = new ContentValues();
        initialValues.put(CASH_PURCHASE_COMPANY, name);
        initialValues.put(CASH_PURCHASE_AMOUNT, amount);
        return mDb.insert(DIALY_PURCHASE_CASH_TABLE, null, initialValues);
    }
public Cursor queueAll() {
        String[] col =  new String[] {KEY_ROWID,
                CASH_PURCHASE_AMOUNT, CASH_PURCHASE_COMPANY, CASH_CREATED_AT};
        Cursor mCursor = mDb.query(DIALY_PURCHASE_CASH_TABLE,col,
                null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }
}

Here is my XML file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:selectorandroid="http://ift.tt/GEGVYd"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:orientation="horizontal">

        <Button
            android:id="@+id/newt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="newtransaction"
            android:text="@string/transaction" />
    </LinearLayout>

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/myFilter"
            android:hint="Search ....">
        <requestFocus />
        </EditText>

        <ListView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/listView21" />
    </LinearLayout>


</LinearLayout>

please can anyone help me out to solve this error.And highlight my mistake

Thankyou.