Joomla custom field type when editing

how do make it so that when I edit an entry, the correct value for my custom field type is selected? I have this so far:

class JFormFieldCustom extends JFormField {

    protected $type = 'Custom';

    // getLabel() left out

    public function getInput() {

            return '<select id="'.$this->id.'" name="'.$this->name.'">'.
                        '<option value="1" >1</option>'.
                        '<option value="2" >2</option>'.
                    '</select>';
    }

}

How do I pass the selected value to this class so I can do:

<option value="1"SELECTED>1</option> 

or

<option value="2" SELECTED>2</option>

Thanks!

Use $this->value to get selected value.Try this-

 class JFormFieldCustom extends JFormField {

        protected $type = 'Custom';

        // getLabel() left out

        public function getInput() {

                return '<select id="'.$this->id.'" name="'.$this->name.'">'.
                            '<option value="1" <?php echo ($this->value==1)?'selected':''?>>1</option>'.
                            '<option value="2" <?php echo ($this->value==2)?'selected':''?>>2</option>'.
                        '</select>';
        }
    }

Hope this will help.