During custom form submission we would want to remember the previous selection. There are many ways to do that, which includes using Sessions and variable_set to set the default value but this is an overkill if you wanted to simply preserve/remember the selection in the next page or after submission. The best way is to use $form_state['storage'] in your submit handler to hoard values between steps.
Consider an example:
<?php
function custom_form_submit($form, &$form_state) {
$start_date = $form_state['values']['startdate'];
$end_date = $form_state['values']['enddate'];
$batch = $form_state['values']['batch'];
// Store values
$form_state['storage']['update_startdate'] = $form_state['values']['startdate'];
$form_state['storage']['update_enddate'] = $form_state['values']['enddate'];
$form_state['storage']['update_batch'] = $form_state['values']['batch'];
// Rebuild the form
$form_state['rebuild'] = TRUE;
// Do other tasks
}
?>
After form rebuild the form would be changed to:
<?php
function custom_form(&$form_state) {
$form = array();
$form['startdate'] = array(
'#type' => 'date_popup',
'#title' => 'Start Date',
'#date_format' => 'Y-m-d',
'#date_label_position' => 'inline',
'#required' => TRUE,
'#tree' => TRUE,
);
//This gets automatically added in form after rebuild
if (isset($form_state['storage']['update_startdate'])) {
$form['startdate']['#default_value'] = $form_state['storage']['update_startdate'];
}
//... Additional form elements
return $form;
}
--
Source: http://stackoverflow.com/questions/1077806/drupal-formwant-to-show-previous-form-value-as-default-value-on-page
?>