Avoid code re-use when handling form validation - php

Question

I am generating form and handling the submit event in the same file.
If user has not entered the title, I want to display the form again and include an error message (e.g. "You forgot the title.").
That means that I have to duplicate code twice - once to diplay empty form and second to display form with body and ask user to enter title:
<?php if(strlen(strip_tags($_POST['posttitle'])) == 0):
// Display the form with question body that user has entered so far and ask user to enter title.
?>
<label for="title"><b>Title:</label><br/>
<input type="text" name="posttitle" id="posttitle" />
<?php endif;?>
<?php elseif ( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action']) && $_POST['action'] == 'post') : ?>
<!-- Everything ok - insert post to DB -->
<?php else :
// just display form here (again ouch!)
<label for="title"><b>Title:</label><br/>
<input type="text" name="posttitle" id="posttitle" />
?>

Answer 1

I would do it like this:
If REQUEST_METHOD is POST I will validate the input and collect messages in an array ($errors in my code).
Then I would just print the form and if there was an error the code will print it.
<?php
$errors = array();
function print_value_for($attr) {
if (isset($_POST[$attr]))
echo $_POST[$attr];
}
function print_error_for($attr) {
global $errors;
if (isset($errors[$attr]))
echo $errors[$attr];
}
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
// do validation here and add messages to $errors
// like $errors['posttitle'] = "The title you entered is bad bad bad";
if (empty($errors)) {
// update database and redirect user
}
}
?>
<!-- display the form and print errors if needed -->
<form>
<?php print_error_for('posttitle'); ?>
<input name="posttitle" type="text" value="<?php print_value_for('posttitle') ?>">
<?php print_error_for('postauthor'); ?>
<input name="postauthor" type="text" value="<?php print_value_for('posttitle') ?>">
<?php print_error_for('postbody'); ?>
<textarea name="postbody">
<?php print_value_for('posttitle') ?>
</textarea>
<input type="submit">
</form>
PS. Consider using MVC to separate code and templates.

Answer 2

Here is a quick way to do that.
<form>
<input type="text" name="title" value="<?php echo $_REQUEST['title']; ?>"/>
<input type="text" name="field_a" value="<?php echo $_REQUEST['field_a']; ?>"/>
....
</form>
But I can also advise you to display a var called $title which is the result of a check on $_REQUEST['title].

Answer 3

You could use an output buffer to grab the form and then assign it to a variable like so:
<?php
ob_start();
include('path/to/your/form');
$form = ob_get_flush();
// then later you can just go
print $form;
?>
Hope this helps

Answer 4

When you display the form, use the possibly empty $_POST values as default field values for both the title and question body. If either is empty, the form will display the second time with the other already filled in:
<?php
$message = "";
if (empty($_POST['title'])) $message .= " Please enter a title.";
if (empty($_POST['body'])) $message .= " Please enter a body.";
?>
<form action='me.php'>
<input name='title' type='text' value='<?php if (!empty($_POST['title'])) echo htmlentities($_POST['title'], ENT_QUOTES); ?>' />
<textarea name='body'><?php if (!empty($_POST['body'])) echo $_POST['body']; ?></textarea>
</form>

Answer 5

Read this MVC
Your can write form in view, handler in controller, and business logic in model