Retaining selected value of drop down list box in post back form data in PHP

Retain a selected option safely

Use an allow-list for accepted option values. The same validated value can then be used to mark the matching option as selected.

$allowed = ['one', 'two', 'three'];
$selected = $_POST['class'] ?? '';

if (!in_array($selected, $allowed, true)) {
    $selected = '';
}

echo '<option value="two"' . ($selected === 'two' ? ' selected' : '') . '>Two</option>';

This is the recommended starting pattern. The detailed examples below are retained for explanation, comparison and related variations.

From a drop down list box or combo box visitor selects one option and submits the form. If the form validation fails then we have to show again the same form asking for changes in input data and submit again. In this process we have to keep our drop down box selected to the option previously selected by the user. For example in a travel information form, visitor select the week day of travel from a drop down list box having all days of the week and submits the form, then due to any reason the form validation fails and we ask the visitor to again fill the form, we must keep the previously selected day of the week of the visitor as selected only. So if the visitor has selected Monday then the form has to show day Monday as selected day of the week.

There are different ways to do this and one method where the data (or the option) are populated from table is already discussed in double drop down list box tutorial. There all options are matched with an if condition and accordingly the selected attribute is added. Note that there are many ways to achieve this and we will try to explore one way here.

We will use the switch function here to assign the selected attribute to one option. We are using header redirection to post back the date entered by the user to the form. Here is the demo of the drop down list box.

Here is the code of the form with decode script.

$t1=$_GET['t1'];
switch ($t1)
{
 case "Mon":
$Mon="selected";
break;
 case "Tue":
$Tue="selected";
break;
 case "Wed":
$Wed="selected";
break;
 case "Thu":
$Thu="selected";
break;
 case "Fri":
$Fri="selected";
break;
 case "Sat":
$Sat="selected";
break;
 case "Sun":
$Sun="selected";
break;
}

echo "
<form method=post action=pb-dropck.php>
<select name=t1>
<option value=Mon $Mon>Mon</option>
<option value=Tue $Tue>Tue</option>
<option value=Wed $Wed>Wed</option>
<option value=Thu $Thu>Thu</option>
<option value=Fri $Fri>Fri</option>
<option value=Sat $Sat>Sat</option>
<option value=Sun $Sun>Sun</option>
</select>
<input type=submit value=Submit>
";

Here is the code for pb-dropck.php file

$t1=$_POST[t1];
header ("Location: pb-drop.php?t1=$t1");

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Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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