Drupal custom form remembering textfield data - php

Question

I am setting up a configuration page for a new module and I am having trouble getting my textfield to remember data I previously entered.
I am setting #default_value by calling variable_get but the value never gets reset in the textfield. It is however correctly stored as a variable and visible on the variable editor page.
Below is a code fragment:
$form = array();
$form['username'] = array(
'#type' => 'textfield',
'#title' => t('Username'),
'#default_value' => variable_get('username', '' ),
'#description' => t('supply the username'),
'#maxlength' => 30,
'#required' => TRUE,
'#weight' => -1,
);
return system_settings_form($form);
How can I fix this?
Updated code
The submit function is as follows:
function mymodule_settings_submit($form, &$form_state){
drupal_set_message('form submit responding : ' . $form_state['values']['username'] );
variable_set( 'username', $form_state['values']['username'] );
}
Updated code #2
The full code:
function my_module_init(){
}
function my_module_menu(){
$items = array();
$items['admin/settings/helper'] = array(
'title' => 'helper',
'page callback' => 'drupal_get_form',
'page arguments' => array('helper_setup'),
'access arguments' => array('access administration pages'),
'type' => MENU_NORMAL_ITEM,
);
return $items;
}
function helper_setup(){
$node_types = node_get_types('names');
$form = array();
$form['username'] = array(
'#type' => 'textfield',
'#title' => t('Username'),
'#default_value' => variable_get('username', '' ),
'#description' => t('supply the username'),
'#maxlength' => 30,
'#required' => TRUE,
'#weight' => -1,
);
$form['#submit'][] = 'my_module_settings_submit';
return system_settings_form($form);
}
function my_module_validate($form, &$form_state){
die('validation area responding!');
}
function my_module_settings_submit($form, &$form_state){
drupal_set_message('form submit responding : ' . $form_state['values']['username'] );
variable_set( 'username', $form_state['values']['username'] );
}

Answer 1

in your form submit function you should insert variable_set('variableName' , 'value') variables is not inserted automatically..
UPDATE:
$form['username'] = array(
'#type' => 'textfield',
'#title' => t('Username'),
'#default_value' => variable_get('username', '' ),
'#description' => t('supply the username'),
'#maxlength' => 30,
'#required' => TRUE,
'#weight' => -1,
);
$form['#submit'][] = '_myform_submit_function' ;
return system_settings_form($form);
now lets build your submit function
function _myform_submit_function($form,&$form_state ) {
variable_set('username', $form_state['values']['username']) ;
drupal_set_message('form submit responding : ' . $form_state['values']['username'] );
}
now clear the cache and tell me if its working or not