使用php和javascript验证html中的多选输入字段

Let's say you have an HTML code like this:

<select multiple="multiple" name="frm_supply[]">
  <option value="s1v1">A</option>
  <option value="s1v2">B</option>
  <option value="s1v3">C</option>
</select>
<select multiple="multiple" name="frm_supply[]">
  <option value="s2v1">1</option>
  <option value="s2v2">2</option>
  <option value="s2v3">3</option>
</select>

When submitting the form, if A, B and 1 are checked, $_POST array will be like this:

Array (
  [frm_supply] => Array (
    [0] => s1v1
    [1] => s1v2
    [2] => s2v1
    )
  )

So, check trough a loop if any <select/> is empty. The following code walks through two <select/>s and displays for each either "List N has values" or "List N is empty".

$countValuesPerList = array();
foreach ($_POST['frm_supply'] as $key => $value)
{
  $index = substr($value, 1, strpos($value, 'v') - 1);
  $countValuesPerList[$index] = true;
}

for ($i = 1; $i <= 2; $i++)
{
  echo isset($countValuesPerList[$i]) && $countValuesPerList[$i] ? 'List ' . $i . ' has values' : 'List ' . $i . ' is empty';
}

Now, to check selections on client side, proceed the same way and check what is selected in each <select/>.

multiple selection values are stored in a array . so check the length of the array and according to ur validation rule, for example for atleast 2 selection ,the length of the array should be greater than 2 and so on

<select name="name">
   <?php
   for ($i = 0; $i < $count; $i++) {
      echo '<option value='$i'>$i</option>';
   }   
   ?>
</select>