When there’s a problem with data entered in a form, you want to print out error messages alongside the problem fields, instead of a generic error message at the top of the form.
You also want to preserve the values the user entered in the form, so they don’t have to redo the entire thing.
As you validate, keep track of form errors in an array keyed by element name. Then, when it’s time to display the form, print the appropriate error message next to each element.
To preserve user input, use the appropriate HTML idiom: a value attribute (with entity encoding) for most <input/> elements, a checked=’checked’ attribute for radio buttons and checkboxes, and a selected=’selected’ attribute on <option/> elements in drop-down menus.
Example 9-22 displays and validates a form with a text box, a checkbox, and a drop-down menu.
Example 9-22. Redisplaying a form with error messages and preserved input
The main logic and validation function:
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// Set up some options for the drop-down menu $flavors = array('Vanilla','Chocolate','Rhinoceros'); // Set up empty defaults when nothing is chosen. $defaults = array('name' => '', 'age' => '', 'flavor' => array()); foreach ($flavors as $flavor) { $defaults['flavor'][$flavor] = ''; } if ($_SERVER['REQUEST_METHOD'] == 'GET') { $errors = array(); include __DIR__ . '/show-form.php'; } else { // The request is a POST, so validate the form $errors = validate_form(); if (count($errors)) { // If there were errors, redisplay the form with the errors, // preserving defaults if (isset($_POST['name'])) { $defaults['name'] = $_POST['name']; } if (isset($_POST['age'])) { $defaults['age'] = "checked='checked'"; } foreach ($flavors as $flavor) { if (isset($_POST['flavor']) && ($_POST['flavor'] == $flavor)) { $defaults['flavor'][$flavor] = "selected='selected'"; } } include __DIR__ . '/show-form.php'; } else { // The form data was valid, so congratulate the user. In "real life" // perhaps here you'd redirect somewhere else or include another // file to display print 'The form is submitted!'; } } function validate_form() { global $flavors; // Start out with no errors $errors = array(); // name is required and must be at least 3 characters if (! (isset($_POST['name']) && (strlen($_POST['name']) > 3))) { $errors['name'] = 'Enter a name of at least 3 letters'; } if (isset($_POST['age']) && ($_POST['age'] != '1')) { $errors['age'] = 'Invalid age checkbox value.'; } // flavor is optional but if submitted must be in $flavors if (isset($_POST['flavor']) && (! in_array($_POST['flavor'], $flavors))) { $errors['flavor'] = 'Choose a valid flavor.'; } return $errors; } |
The form (show-form.php):
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<form action='<?= htmlentities($_SERVER['SCRIPT_NAME']) ?>' method='post'> <dl> <dt>Your Name:</dt> <?php if (isset($errors['name'])) { ?> <dd class="error"><?= htmlentities($errors['name']) ?></dd> <?php } ?> <dd><input type='text' name='name' value='<?= htmlentities($defaults['name']) ?>'/></dd> <dt>Are you over 18 years old?</dt> <?php if (isset($errors['age'])) { ?> <dd class="error"><?= htmlentities($errors['age']) ?></dd> <?php } ?> <dd><input type='checkbox' name='age' value='1' <?= $defaults['age'] ?>/> Yes</dd> <dt>Your favorite ice cream flavor:</dt> <?php if (isset($errors['flavor'])) { ?> <dd class="error"><?= htmlentities($errors['flavor']) ?></dd> <?php } ?> <dd><select name='flavor'> <?php foreach ($flavors as $flavor) { ?> <option <?= isset($defaults['flavor'][$flavor]) ? $defaults['flavor'][$flavor] : "" ?>><?= htmlentities($flavor) ?></option> <?php } ?> </select></dd> </dl> <input type='submit' value='Send Info'/> </form> |
When a form is submitted with invalid data, it’s more pleasant for the user if the form is redisplayed with error messages in appropriate places rather than a generic the form is invalid message at the top of the form.
The validate_form() function in Example 9-22 builds up an array of error messages that the form display code uses to print the messages in the right places.
Extending Example 9-22 is a matter of expanding the checks in validate_form() to handle the appropriate validation needs of your form and including the correct HTML generation in show-form.php so that the form includes the input elements you want.
