Multiple Select with Explode: only returns the word "Array"

Question

Using Wordpress I have created a multiple select box so that users can select categories to exclude. When the page initially loads I see my default values pre-selected. However when I select new values and save... I only see the word "Array" echoed and nothing selected?

<select class="amultiple" id="<?php echo $value['id']; ?>"  name="<?php echo $value['id']; ?>[]" multiple="multiple" size="8">
      <?php 
       global $options;
        foreach ($options as $value) {
         if (get_settings( $value['id'] ) === FALSE) { $$value['id'] = $value['std']; } else { $$value['id'] = get_settings( $value['id'] ); 
         }
        }
        $categories = &get_categories('type=post&orderby=name&hide_empty=1');
        if ($categories) {
         $ex_cat = implode(',', $tt_cat_exclude);

         foreach ($categories as $category) {
          $selected = (in_array($ex_cat, $category->cat_ID)) ? ' selected="selected"' : '';
          echo '<option value="' . $category->cat_ID . '"' . $selected . '>' . $category->cat_name . '</option>' . "\n";
         }
        }
?>
</select>
<br />For testing purposes, print variables: <?php echo $ex_cat; ?>

http://i48.tinypic.com/k9e3qq.gif

Answer 1

Looks like tt_cat_exclude is missing it's opening $

Answer 2

When you postback, the field tt_cat_exclude is an array of the values that you've set - because you've name it tt_cat_exclude[] with a [] behind.

Example:

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<select class="amultiple" id="tt_cat_exclude"  name="tt_cat_exclude[]" multiple="multiple" size="8">
  <option value="1">TestingA</option>
  <option value="2">TestingB</option>
  <option value="3">TestingC</option>
  <option value="4">TestingD</option>
  <option value="5">TestingE</option>
 </select>
<input type="submit" value="Submit" />
</form>
<br/><br/>For testing purposes: <?php

if(isset($_POST['tt_cat_exclude'])){
  var_dump($_POST['tt_cat_exclude']); // outputs an array of the selected values
}

?>

Answer 3

name="tt_cat_exclude[]" means you're defining an array, so it's normal for the output to be "array"

for testing try print_r (outputs the whole architecture of the variable) or var_dump (outputs the var type too)

Answer 4

You should use implode()

Like so

$ex_cat = implode(',', $tt_cat_exclude);

This will return a comma separated list

This line should be

$selected = (in_array($category->cat_ID, $ex_cat)) ? ' selected="selected"' : '';

Changed to

$selected = (in_array($category->cat_ID, $tt_cat_exclude)) ? ' selected="selected"' : '';

Since the $ex_cat is a string and cannot be used in in_array()

The $ex_cat is now redundant i guess.