PHP: Sticky Forms

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Sticky Forms

Aims:

• to reinforce understanding of self-processing pages
• to know what a sticky form is, and how to write one

Sticky Forms

• A sticky form is one that displays the values of the previous request
• In other words, if you submit some data using the form and the form is then re-displayed, the text fields are re-displayed with your data still in them
• This idea is often combined with self-processing pages
• We will modify head_to_hat.php to make the form sticky

Sticky forms

• One of the attributes of a text field is particularly useful for sticky forms
  Class exercise: Which one?
• It's all made even easier by the output_textfield function, whose prototype is as follows:
  void output_textfield( $id, $label, $name, $size, $maxlength,
    $value, $is_disabled )
  Class exercise: Which parameter makes life easier for us?
• All we need to do is modify the output_form_page function

Sticky forms

function output_form_page( $hat_size )
{
    output_header('Hat Trick!', 'stylesheet.css');
    echo "<form action=\"{$_SERVER['PHP_SELF']}\" method=\"get\">";
    if ( isset($_GET['circumference']) )
    {
        output_textfield('circumference', 'Circumference: ', 'circumference', 2, 2, 
            $_GET['circumference'], false);
    }
    else
    {
        output_textfield('circumference', 'Circumference: ', 'circumference', 2, 2, 
            '', false);
    }
    output_textfield('hat_size', 'Hat size: ', 'hat_size', 4, 4, $hat_size, true);
    output_submit_button('Submit');        
    echo "</form>";
    output_footer('University College Cork');    
}

Shorter version using the conditional operator

function output_form_page( $hat_size )
{
    output_header('Hat Trick!', 'stylesheet.css');
    echo "<form action=\"{$_SERVER['PHP_SELF']}\" method=\"get\">";
    output_textfield('circumference', 'Circumference: ', 'circumference', 2, 2, 
            isset($_GET['circumference']) ? $_GET['circumference'] : '', false);
    output_textfield('hat_size', 'Hat size: ', 'hat_size', 4, 4, $hat_size, true);
    output_submit_button('Submit'); 
    echo "</form>";
    output_footer('University College Cork');    
}

Class exercise

• Rewrite our latest version of head_to_hat.php:
  • include validation of user data
  • put error messages, if any, onto the sticky form
  • assume there is a validation function with the following prototype:
    float get_required_float( &$user_data, $name, $label, $maxlength,
    &$errors, $min, $max )

Final obervations

• Password fields are usually not sticky
• Making radio buttons sticky is a little harder
• Making checkboxes sticky is harder still
• These are left to advanced students as optional activities