Web Programming Step by Step, 2nd Edition

Lecture 9: Forms

Reading: 6.1 - 6.2, 6.4

Except where otherwise noted, the contents of this document are Copyright 2012 Marty Stepp, Jessica Miller, and Victoria Kirst. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the author's expressed written permission.

Web data

• most interesting web pages revolve around data
  • examples: Google, IMDB, Digg, Facebook, YouTube, Rotten Tomatoes
  • can take many formats: text, HTML, XML, multimedia
• many of them allow us to access their data
• some even allow us to submit our own new data
• most server-side web programs accept parameters that guide their execution

Query strings and parameters

URL?name=value&name=value...

http://www.google.com/search?q=Romney
http://example.com/student_login.php?username=stepp&id=1234567

• query string: a set of parameters passed from a browser to a web server
  • often passed by placing name/value pairs at the end of a URL
  • above, parameter username has value stepp, and sid has value 1234567
• PHP code on the server can examine and utilize the value of parameters
• a way for PHP code to produce different output based on values passed by the user

Query parameters: $_GET, $_POST

$user_name = $_GET["username"];
$id_number = (int) $_GET["id"];
$eats_meat = FALSE;
if (isset($_GET["meat"])) {
	$eats_meat = TRUE;
}

• $_GET["parameter name"] or $_POST["parameter name"] returns a GET/POST parameter's value as a string
• parameters specified as http://....?name=value&name=value are GET parameters
• test whether a given parameter was passed with isset

Example: Exponents

$base = $_GET["base"];
$exp = $_GET["exponent"];
$result = pow($base, $exp);
print "$base ^ $exp = $result";

exponent.php?base=3&exponent=4

Example: Print all parameters

<?php foreach ($_GET as $param => $value) { ?>
	<p>Parameter <?= $param ?> has value <?= $value ?></p>
<?php } ?>

print_params.php?name=Marty+Stepp&sid=1234567

• or call print_r or var_dump on $_GET for debugging

HTML forms

• form: a group of UI controls that accepts information from the user and sends the information to a web server
• the information is sent to the server as a query string
• JavaScript can be used to create interactive controls (seen later)

HTML form: <form>

<form action="destination URL">
	form controls
</form>

• required action attribute gives the URL of the page that will process this form's data
• when form has been filled out and submitted, its data will be sent to the action's URL
• one page may contain many forms if so desired

Form example

<form action="http://www.google.com/search">
	<div>
		Let's search Google:
		<input name="q" />
		<input type="submit" />
	</div>
</form>

• must wrap the form's controls in a block element such as div

Form controls: <input>

<!-- 'q' happens to be the name of Google's required parameter -->
<input type="text" name="q" value="Colbert Report" />
<input type="submit" value="Booyah!" />

• input element is used to create many UI controls
  • an inline element that MUST be self-closed
• name attribute specifies name of query parameter to pass to server
• type can be button, checkbox, file, hidden, password, radio, reset, submit, text, ...
• value attribute specifies control's initial text

Text fields: <input>

<input type="text" size="10" maxlength="8" /> NetID <br />
<input type="password" size="16" /> Password
<input type="submit" value="Log In" />

• input attributes: disabled, maxlength, readonly, size, value
• size attribute controls onscreen width of text field
• maxlength limits how many characters user is able to type into field

Text boxes: <textarea>

a multi-line text input area (inline)

<textarea rows="4" cols="20">
Type your comments here.
</textarea>

• initial text is placed inside textarea tag (optional)
• required rows and cols attributes specify height/width in characters
• optional readonly attribute means text cannot be modified

Checkboxes: <input>

yes/no choices that can be checked and unchecked (inline)

<input type="checkbox" name="lettuce" /> Lettuce
<input type="checkbox" name="tomato" checked="checked" /> Tomato
<input type="checkbox" name="pickles" checked="checked" /> Pickles

• none, 1, or many checkboxes can be checked at same time
• when sent to server, any checked boxes will be sent with value on:

  • http://webster.cs.washington.edu/params.php?tomato=on&pickles=on
    

• use checked="checked" attribute in HTML to initially check the box

Radio buttons: <input>

sets of mutually exclusive choices (inline)

<input type="radio" name="cc" value="visa" checked="checked" /> Visa
<input type="radio" name="cc" value="mastercard" /> MasterCard
<input type="radio" name="cc" value="amex" /> American Express

• grouped by name attribute (only one can be checked at a time)
• must specify a value for each one or else it will be sent as value on

Text labels: <label>

<label><input type="radio" name="cc" value="visa" checked="checked" /> Visa</label>
<label><input type="radio" name="cc" value="mastercard" /> MasterCard</label>
<label><input type="radio" name="cc" value="amex" /> American Express</label>

• associates nearby text with control, so you can click text to activate control
• can be used with checkboxes or radio buttons
• label element can be targeted by CSS style rules

Reset buttons

Name: <input type="text" name="name" /> <br />
Food: <input type="text" name="meal" value="pizza" /> <br />
<label>Meat? <input type="checkbox" name="meat" /></label> <br />
<input type="reset" />

• when clicked, returns all form controls to their initial values
• specify custom text on the button by setting its value attribute

Hidden input parameters

<input type="text" name="username" /> Name <br />
<input type="text" name="sid" /> SID <br />
<input type="hidden" name="school" value="UW" />
<input type="hidden" name="year" value="2048" />

• an invisible parameter that is still passed to the server when form is submitted
• useful for passing on additional state that isn't modified by the user

Styling form controls

element[attribute="value"] {
	property : value;
	property : value;
	...
	property : value;
}

input[type="text"] {
	background-color: yellow;
	font-weight: bold;
}

• attribute selector: matches only elements that have a particular attribute value
• useful for controls because many share the same element (input)