Views - Exposed Filter - Multi Select List Modify into a Autocomplete Text Field

I have the same problem.
Instead of "contact" content type I have "article" one,
instead of "organization" contenet type I have "author".

First step: In views.module I' ve found function views_form_alter and changed it:

if ($form_id == 'profile_field_form')
{
views_invalidate_cache();
}
// I have added this code
if ($form_id == 'views_filters')
{
$form['filter0']['#type']='textfield';
$form['filter0']['#autocomplete_path']='author/autocomplete';
}

And, really, I saw the result - the type of widget was changed to autocomplete text field.

Than I've taken the second step changing the function views_menu in views.module:

function views_menu($may_cache) {
   $items = array();
   if ($may_cache) {
    $items[] = array(
    'path' => 'author/autocomplete',
    'callback' => 'author_autocomplete',   
    'type' => MENU_CALLBACK,
    'access' => TRUE,
    );
  }
/* I've commented this 
if ($may_cache)
{
views_load_cache();
if (arg(0) == 'admin' && arg(2) =='modules')
{
views_invalidate_cache();
}
views_menu_standard_items($items);
}
else
{
views_menu_inline_items($items);
}
*/


  return $items;
}

Now when I am trying to input something in my autocomplete field for authors I get a 404 mistake: http://mysite/author/autocomplete not found.
What should I do to fix it?

subscribe.

So I just had to do the same thing for a Content Taxonomy Field.
Thank you swolynski for posting. I had some 'An illegal choice' errors to work through, on my version, I prefill the field with All, and have it go away when user selects the box. Also if the user puts in an illegal choice, I give them a drupal message saying that they have put in a choice that is not valid, and again prefill the box with All.

<?php

function mymodule_menu() {
  $items = array();
  $items['mymodule/autocomplete'] = array(
    'title' => t('mymodule'),
    'page callback' => 'mymodule_autocomplete',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK
    );
  return $items;
}

//--alter form - change select to textfield & autocomplete
function mymodule_form_alter(&$form, $form_state, $form_id) {
//only change for this view display exposed form.
//drupal_set_message($form['#id']);
  //my exposed view pages to use it on.
  $my_views_ids = array('views-exposed-form-mymodule-page-1', 
                        'views-exposed-form-mymodule-page-2', 
                        'views-exposed-form-mymodule-page-3',
                        'views-exposed-form-mymodule-page-4'
                        ); 

  if (in_array($form['#id'], $my_views_ids)) {  
    //drupal_set_message($form['#id']);
    if (array_key_exists('view', $form_state)) {
      if (array_key_exists('name', $form_state['view'])) {          
          global $send_message_once;
          $options = Array();
          $vocab = (taxonomy_get_tree(13));
          $options["All"] = '';
          foreach ($vocab as $term) {
           $options[$term->name] = $term->tid;
          }
          $exposed_filter_values = ($form_state['view']->get_exposed_input());
          if (!($exposed_filter_values['field_myfield_value'])) {
            $form['field_myfield_value']['#value']='All'; 
            $form['field_myfield_value']['#attributes']= array('onfocus' => 'this.value=""');
          }
          else {
           if (!(array_key_exists(($exposed_filter_values['field_myfield_value']), $options))) {
             if (!($send_message_once)) {
               drupal_set_message('There are no Operators named "'. $exposed_filter_values['field_myfield_value'] .'"');
               $send_message_once=TRUE;
              }
             $form['field_myfield_value']['#value']='All'; 
             $form['field_myfield_value']['#attributes']= array('onfocus' => 'this.value=""');
           }
          }
          $form['field_myfield_value']['#type']='textfield';
          $form['field_myfield_value']['#autocomplete_path']='mymodule/autocomplete';
          $form['field_myfield_value']['#size']='28'; 
          $form['field_myfield_value']['#options'] = $options;
      }
    }
  }
}

//--process autocomplete - query db for matches and send back to form for display
function mymodule_autocomplete($string = '') {
  $matches = array();
  if ($string) {
    $string = trim($string);
    {
      //matches from the beginning of the title - use '%%%s%%' to match from anywhere in the title
      $query = "
        SELECT term_data.tid AS tid,
        term_data.name AS term_data_name,
        term_data.vid AS term_data_vid
        FROM term_data term_data 
        LEFT JOIN vocabulary vocabulary ON term_data.vid = vocabulary.vid
        WHERE vocabulary.vid = '13' and term_data.name like '%s%%'
      ";
      
      $result = db_query_range($query,$string,0,10);
      if ($result != false) {
        while ($mytermname = db_fetch_object($result)) {
          $matches[$mytermname->term_data_name] = check_plain($mytermname->term_data_name);
        }
      }
    }
  }
  print drupal_to_js($matches);
  exit();
}

//--change term names to tids.
function mymodule_views_query_alter(&$view, &$query) {
  if (is_array($query->where)){
    if (count($query->where) >= 1) {
      $index_value = array_search("node_data_field_myfield.field_myfield_value = '%s'", $query->where[0][clauses]);
      if ($index_value) {
        $mynodename_title = $query->where[0][args][$index_value];
        if ($mynodename_title != '' && $mynodename_title != "**All**" && $mynodename_title != "OR") {
          $mynodename_nid = db_result(db_query("SELECT term_data.tid AS tid FROM term_data term_data WHERE (term_data.vid in ('13')) AND (term_data.name = '%s')",$mynodename_title));
         $query->where[0][args][$index_value] = $mynodename_nid;
        }
      }
    }
  }
}


?>

I think I figured out an easier way to avoid the 'An illegal choice has been detected. Please contact the site administrator.' error message. Instead of generating the allowed options, remove #options using unset(). Without #options, the validation doesn't require that the user selected a valid option.

If they entered text that will not match a node id, I set the node id to 0 in the query. This makes it work properly, returning no results without throwing errors.

Here's my .module code for Drupal 6.x:

// $Id: MODULE_NAME.module

/**
*@file
* Module Name
* Turns a select into an autocomplete textfield.
*
* Specific for 'NODE_NAME' nodes and the 'VIEW_NAME' view 
* 
*/

/**
* Implementation of hook_menu().
*/
function MODULE_NAME_menu(){
	
//Initialize the $items array.
    $items = array();
	
//Add menu for the node autocomplete textfield's #autocomplete_path.
    $items['NODE_NAME/autocomplete'] = array(
//Required. The untranslated title of the menu item.
        'title' => t('Node Title'),
//The function to call to display a web page when the user visits the path. If omitted, the parent menu item's callback will be used instead.
        'page callback' => 'NODE_NAME_autocomplete',
//An array of arguments to pass to the access callback function. Integer values pass the corresponding URL component.
        'access arguments' => array('access content'),
//Callbacks simply register a path so that the correct function is fired when the URL is accessed.
        'type' => MENU_CALLBACK
    );
	
//Return the $items array with the new menu item.
    return $items;
}

/**
* Implementation of hook_form_alter().
*/
function MODULE_NAME_form_alter(&$form, $form_state, $form_id){

//Only affect a views exposed form.
    if($form_id == 'views_exposed_form'){
		
//If a view exists, retreive form_state information.
        if (array_key_exists('view', $form_state)){
			
//If the view has a name,
            if (array_key_exists('name', $form_state['view'])){
				
//Only affect the specified view.
                if ($form_state['view']->name == 'VIEW_NAME'){
					
//Turn the node select into a textfield.
                    $form['SELECT_FIELD']['#type'] ='textfield';
//Turns the node textfield into an autocomplete textfield.					
                    $form['SELECT_FIELD']['#autocomplete_path'] ='NODE_NAME/autocomplete';
//Remove options from the node autocomplete textfield so errors aren't thrown if the user enters something that doesn't exist.
					unset($form['SELECT_FIELD']['#options']);
                }
            }
        }
    }
}

/**
* Autocomplete Function for nodes.
*/
function NODE_NAME_autocomplete($string = ''){
	
//Initialize the $matches array.
    $matches = array();
	
//Ensure that a string has been passed.	
    if ($string){
		
//Remove any extra spaces before or after the meaningful string.		
        $string = trim($string);
		
//Set the query to select all nodes that are published and match what the user entered. - use '%%%s%%' to match from anywhere in the title
		$query = "SELECT title FROM {node} WHERE type='NODE_NAME' and title like '%s%'";
//Run the query and restrict the results to the first 10.
		$result = db_query_range($query,$string,0,10);
		
//Ensure there are results returned from the query.		
		if ($result != false){
			
//Loop through the all of the results.
			while ($NODE_NAME = db_fetch_object($result)){
				
//Add the plain text select field to the $matches array with the $key set as the same.			
				$matches[$NODE_NAME->title] = check_plain($NODE_NAME->title);
			}
		}
    }

//Converts the $matches array into its Javascript equivalent and prints it to the page output.		
    print drupal_to_js($matches);
//Exit the function.	
    exit;
}

/**
* Implementation of hook_views_query_alter().
*/
function MODULE_NAME_views_query_alter(&$view, &$query){
	
//Ensure that the WHERE information exists as an array in the query which is not empty.
    if (is_array($query->where) && !empty($query->where)){

//Search the where clauses for the select field clause.
		$index_value = array_search("node_data_SELECT_FIELD.SELECT_FIELD = '%s'", $query->where[0][clauses]);

//If the select field clause was found,		
		if ($index_value != '' && $index_value != false){

//If the cooresponding argument is not blank or all,
			if($query->where[0][args][$index_value] == '' || strtolower($NODE_NAME_title) == "all"){

//remove the clause and argument because the user isn't searching by the select field.
				unset($query->where[0][clauses][$index_value]);	
				unset($query->where[0][args][$index_value]);	
			}
			else{
//Get the argument that cooresponds to the select field where clause.
				$NODE_NAME_title = strtoupper($query->where[0][args][$index_value]);
				
//Select the node id of the select field argument.
				$NODE_NAME_nid = db_result(db_query("SELECT nid FROM {node} WHERE title = '%s'",$NODE_NAME_title));
				
//If a node id was found for the select field argument,
				if($NODE_NAME_nid){

//replace the select field with the cooresponding node id in the argument.
					$query->where[0][args][$index_value] = $NODE_NAME_nid;
				}
				else{
//If the node id wasn't found, replace the select field with 0 as a nonexistent node id that will not return results.				
					$query->where[0][args][$index_value] = 0;
				}
			}
		}
	}
}

I have done this recently by using taxonomy code example. Mine was for Node Title Auto complete, but I think you'll be able to get it from here.

function _node_title_autocomplete($string) {
  // The user enters a comma-separated list of Titles. We only autocomplete the last title.
  // This code was altered from core taxonomy autocomplete.
  $array = drupal_explode_tags($string);
  // Fetch last Title
  $last_string = trim(array_pop($array));
  $matches = array();
  if ($last_string != '') {
    $result = db_query_range("SELECT node.nid, node.title FROM {node} WHERE LOWER(node.title) LIKE LOWER('%s%%') AND node.type in ('competitor')", $last_string, 0, 10);
    $prefix = count($array) ? implode(', ', $array) .', ' : '';
    while ($node = db_fetch_object($result)) {
      $n = $node->title;
      // Commas and quotes in terms are special cases, so encode 'em.
      if (strpos($node->title, ',') !== FALSE || strpos($node->title, '"') !== FALSE) {
        $n = '"'. str_replace('"', '""', $node->title) .'"';
      }
      $matches[$prefix . $n] = check_plain($node->title);
    }
  }
  drupal_json($matches);
}

i'm hoping to implement this for a Views 3.x exposed filter allowed values (or not?) select list (transformed to autocomplete textfield of course). I've been researching and there are lots of bits of code around for how to do this with Views 2.x as well as Views Autocomplete Filters module... but i cannot find anything related to how to do adjust the code like the above example in Views 3.x for a cck field. Could anyone help me out? Am i missing something?

I'd also be more than happy to pay someone $$ to help me get a working Views exposed filter cck autocomplete widget for views 3.x