PHP: More Forms and Scripts

Derek Bridge

Department of Computer Science,
University College Cork

PHP: More Forms and Scripts

Aims:

to review what we've learned with a simple example
to learn how to create self-processing pages
to learn how to create sticky forms
to learn how to use a sticky form for data validation

langform.html: an (X)HTML form with checkboxes

<form action="langscript.php" method="get">
  <p>
   Which of these do you know?
  </p>
  <p>
   <input type="checkbox" name="langs[]" value="Groovy" id="groovyBox" />
   <label for="groovyBox">Groovy</label>
   <input type="checkbox" name="langs[]" value="Java" id="javaBox" />
   <label for="javaBox">Java</label>
   <input type="checkbox" name="langs[]" value="PHP" id="phpBox" />
   <label for="phpBox">PHP</label>
  </p>
  <p>
   <input type="submit" value="Submit" />;
  </p>
</form>

Groups of checkboxes

To create a group of checkboxes,
- each checkbox is given the same name attribute
- a name and value will be passed to the server for each box the user checks
- to ensure that PHP handles the multiple values correctly, the name must end with []
<input type="checkbox" name="langs[]" value="Groovy" /> <input type="checkbox" name="langs[]" value="Java" /> <input type="checkbox" name="langs[]" value="PHP" />
In the PHP script, $_GET['langs'] contains an indexed array, not a string (hence $_GET is an array that contains an array!)

`langscript.php`

<?php
  if ( ! isset($_GET['langs']) ) 
  {
     die('No languages! Are you stupid?');
  }
  $length = count($_GET['langs']);
  echo "You know the following {$length} languages:"; 
  echo '<ul>';
  foreach ($_GET['langs'] as $lang) 
  {
    echo "<li>$lang</li>";
  }
  echo '</ul>';
 ?>

Notes on `langscript.php`

We know that $_GET is an associative array
But, as mentioned, $_GET['langs'] is itself an indexed array
We then print it in an (X)HTML list, similar to an earlier lecture:
echo '<ul>'; foreach ($_GET['langs'] as $lang) { echo "<li>$lang</li>"; } echo '</ul>';

Notes on `langscript.php`

The example also shows:
- if the user checked none of the boxes, no data is sent to the server and so $_GET['langs'] has not been set
- we have checked for this using the isset function
- the die function, outputs its argument and ends execution of the script (but look at the source of the output!)
- the count function returns the length of the array
Class exercise: Sometimes this script outputs "You know the following 1 languages". How can you improve this?

Self-processing pages: example

We have been using two files: an (X)HTML form and a PHP script

We can use one file: a PHP script that both generates the form and processes it

<?php
  $output = '';
  if ( isset($_GET['submitted']) ) 
  {
     $celsius = ($_GET['fahr'] - 32) * 5/9;
     $output = "{$_GET['fahr']} Fahrenheit is $celsius Celsius";
 }
?>

<?php echo '<?xml version="1.0" encoding="UTF-8"?>'; ?>
<!DOCTYPE html 
 PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
  <title>Temperature conversion</title>
  <link rel="stylesheet" type="text/css" href="formlayout.css" />
</head>

<body>
<form action="<?php echo $_SERVER['PHP_SELF'] ?>" method="get">
  <p>
   <label for="fahrField">Fahrenheit:</label>
   <input type="text" name="fahr" id="fahrField" />
  </p>
  <p>
   <input type="submit" name="submitted" value="Convert" />
  </p>
  <p>
   <?php echo $output ?>
  </p>
</form>
</body>
</html>

Self-processing pages: observations

Note the trick for putting the name of this file into the action attribute
Early in the script we assign a string into $output showing the results of our temperature conversion
Then, in the form, we echo the value of $output
Problem! The first time we show the form to the user,
- we haven't any user input,
- we don't want to do a conversion, and
- we don't want to show any output
How can we tell whether this is the first time we are showing the form to the user?
One solution.
1. Use a name attribute on the submit button:
  <input type="submit" name="submitted" value="Convert" />
2. Test whether there is an entry with this key in $_GET
  if ( isset($_GET['submitted']) ) ...
  If it is set, the user must have pressed submit, so this is not the first time we are showing the form to the user





Sticky forms: example


 A sticky form displays the values of the previous query
 Here's some changes that don't seem too important...

<?php 
 $fahr = '';
 $output = '';
 if ( isset($_GET['submitted']) ) 
 {
    $fahr = $_GET['fahr'];
    $celsius = ($fahr - 32) * 5/9;
    $output = "{$fahr} Fahrenheit is {$celsius} Celsius";
 }
?>


 But they allow one crucial change to the text-field in the form...

   <input type="text" name="fahr" id="fahrField"
             value="<?php echo $fahr; ?>" />






Sticky forms for user data validation


 We often need to validate the user's data
  
   e.g. to check something has been entered into a field
   e.g. to check that what is entered is numeric
  
 
 If there's an error, we display a message
  
   Sticky forms are good for this because they can preserve what the user
       has already typed so s/he doesn't have to retype everything
  
 






Validation: example

<?php 
 $fahr = '';
 $output = '';
 if ( isset($_GET['submitted']) ) 
 {
    $fahr = $_GET['fahr'];
    if ( ! is_numeric($fahr) ) 
    {
       $output = "You must enter a numeric value";
    }
    else
    {	

       $celsius = ($fahr - 32) * 5/9;
       $output = "{$fahr} Fahrenheit is {$celsius} Celsius";
    }
 }
?>

PHP: More Forms and Scripts

Derek Bridge

Department of Computer Science, University College Cork

PHP: More Forms and Scripts

langform.html: an (X)HTML form with checkboxes

Groups of checkboxes

langscript.php

Notes on langscript.php

Notes on langscript.php

Self-processing pages: example

Self-processing pages: observations

Sticky forms: example

Sticky forms for user data validation

Validation: example

Department of Computer Science,
University College Cork

`langscript.php`

Notes on `langscript.php`

Notes on `langscript.php`