Question

OK, I’ve read around and see that Java only passes by value, not by reference so I don’t know how to accomplish this.

• I’ve 6 Spinners in an Android Activity that are populated with different SQLite queries.
• The code to populate each Spinner and set the OnItemSelectedListener is very similiar so I was hoping to refactor to one method and call it 6 times with each Spinner ID and Sqlite query.

• How do I get the Spinner onItemSelectedListener to change the right instance member on each different Spinner?

  public void fillSpinner(String spinner_name, final String field_name) {
  // This finds the Spinner ID passed into the method with spinner_name
  // from the Resources file. e.g. spinner1
  int resID = getResources().getIdentifier(spinner_name, "id",
          getPackageName());
  Spinner s = (Spinner) findViewById(resID);
  final Cursor cMonth;
  // This gets the data to populate the spinner, e.g. if field_name was
  // strength = SELECT _id, strength FROM cigars GROUP BY strength
  cMonth = dbHelper.fetchSpinnerFilters(field_name);
  startManagingCursor(cMonth);
  String[] from = new String[] { field_name };
  int[] to = new int[] { android.R.id.text1 };
  SimpleCursorAdapter months = new SimpleCursorAdapter(this,
          android.R.layout.simple_spinner_item, cMonth, from, to);
  months.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
  s.setAdapter(months);
  // This is setting the Spinner Item Selected Listener Callback, where
  // all the problems happen
  s.setOnItemSelectedListener(new OnItemSelectedListener() {
      public void onItemSelected(AdapterView<?> parent, View view,
              int position, long id) {
          Cursor theCursor = (Cursor) parent.getSelectedItem();
          // This is the problem area.
          object_reference_to_clas_member_of_field_name = theCursor
                  .getString(theCursor.getColumnIndex(field_name));
      }
  
      public void onNothingSelected(AdapterView<?> parent) {
          // showToast("Spinner1: unselected");
      }
  });
  

  }

You call this method like this fillSpinner("spinner1","strength");.

It finds the spinner with id spinner1 and queries the database for the strength field. field_name, which is strength in this example had to be declared a final variable to be used in the onItemSelectedListener or I’d get the error Cannot refer to a non-final variable field_name inside an inner class defined in a different method.

But how do I get the onItemSelectedListener to change the value of a different instance member when each different Spinner is used? This is the all important line of code:
object_reference_to_clas_member_of_field_name = theCursor .getString(theCursor.getColumnIndex(field_name));

I can’t use a final String as the variable will obviously change when the user selects a different value. I’ve read around a good bit and am stumped to a solution. I can just copy and paste this code 6 times and forget about refactoring but I’d really like to know the elegant solution. Post a comment if you don’t understand my question, I’m not sure if I explaned myself well.

Answer 1

You can do it, by passing additional class as parameter of fillSpinner method:

A. Create interface

public interface OnSpinnerValueSelected {
    void onValueSelected(String selectedValue);
}

B. Change your method a bit:

public void fillSpinner(String spinner_name, final String field_name,
                    final OnSpinnerValueSelected valueChangeListener) {

    // Prepare spinner

    s.setOnItemSelectedListener(new OnItemSelectedListener() {

        public void onItemSelected(AdapterView<?> parent, View view,
                     int position, long id) {
            Cursor theCursor = (Cursor) parent.getSelectedItem();

            valueChangeListener.onValueSelected(theCursor
                           .getString(theCursor.getColumnIndex(field_name)));
        }

        public void onNothingSelected(AdapterView<?> parent) {

        }
    });
}

C. provide listener:

fillSpinner("spinner1","strength", new OnSpinnerValueSelected() {
    public void onValueSelected(String selectedValue) {
        yourObject.setField(selectedValue);
    }
});