How can the values selected in one selection box be retained when selecting values in another box in PHP?

To retain the values selected in one selection box when selecting values in another box in PHP, you can use sessions to store the selected values. When a value is selected in the first selection box, store it in a session variable. Then, when the second selection box is loaded, check if the session variable exists and pre-select the value accordingly. 

<?php
session_start();

$selectedValue1 = isset($_SESSION['selectedValue1']) ? $_SESSION['selectedValue1'] : '';
$selectedValue2 = isset($_POST['selection2']) ? $_POST['selection2'] : '';

// Store selected value from selection box 1 in session
if(isset($_POST['selection1'])){
    $_SESSION['selectedValue1'] = $_POST['selection1'];
}

?>

<form method="post">
    <select name="selection1">
        <option value="value1" <?php if($selectedValue1 == 'value1') echo 'selected'; ?>>Value 1</option>
        <option value="value2" <?php if($selectedValue1 == 'value2') echo 'selected'; ?>>Value 2</option>
    </select>
    
    <select name="selection2">
        <option value="value3" <?php if($selectedValue2 == 'value3') echo 'selected'; ?>>Value 3</option>
        <option value="value4" <?php if($selectedValue2 == 'value4') echo 'selected'; ?>>Value 4</option>
    </select>
    
    <input type="submit" value="Submit">
</form>

Keywords

PHP form handling session variables AJAX dynamic web development

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