Web Programming Step by Step

Lecture 9
HTML Forms

Reading: 6.1 - 6.2, 6.4

Except where otherwise noted, the contents of this presentation are Copyright 2010 Marty Stepp and Jessica Miller.

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 (6.1.1)

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

http://www.google.com/search?q=Obama
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: $_REQUEST (6.4.2)

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

• $_REQUEST["parameter name"] returns a parameter's value as a string
• test whether a given parameter was passed with isset

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> (6.1.2)

<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> (6.2.1)

<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> (6.2.2)

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> (6.2.3)

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> (6.2.4)

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> (6.2.5)

<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

Drop-down list: <select>, <option> (6.2.6)

menus of choices that collapse and expand (inline)

<select name="favoritecharacter">
	<option>Jerry</option>
	<option>George</option>
	<option selected="selected">Kramer</option>
	<option>Elaine</option>
</select>

• option element represents each choice
• select optional attributes: disabled, multiple, size
• optional selected attribute sets which one is initially chosen

Using <select> for lists

<select name="favoritecharacter[]" size="3" multiple="multiple">
	<option>Jerry</option>
	<option>George</option>
	<option>Kramer</option>
	<option>Elaine</option>
	<option selected="selected">Newman</option>
</select>

• optional multiple attribute allows selecting multiple items with shift- or ctrl-click
  • must declare parameter's name with [] if you allow multiple selections
• option tags can be set to be initially selected

Option groups: <optgroup>

<select name="favoritecharacter">
	<optgroup label="Major Characters">
		<option>Jerry</option>
		<option>George</option>
		<option>Kramer</option>
		<option>Elaine</option>
	</optgroup>
	<optgroup label="Minor Characters">
		<option>Newman</option>
		<option>Susan</option>
	</optgroup>
</select>

• What should we do if we don't like the bold italic?

Reset buttons (6.2.7)

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

Common UI control errors

• I changed the form's HTML code ... but when I refresh, the page doesn't update!
  • By default, when you refresh a page, it leaves the previous values in all form controls
  • it does this in case you were filling out a long form and needed to refresh/return to it
  • if you want it to clear out all UI controls' state and values, you must do a full refresh
    • Firefox: Shift-Ctrl-R
    • Mac: Shift-Command-R

Hidden input parameters (6.3.2)

<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

Example: Exponents

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

http://example.com/exponent.php?base=3&exponent=4

Example: Print all parameters

<?php
foreach ($_REQUEST as $param => $value) {
	?>

	<p>Parameter <?= $param ?> has value <?= $value ?></p>

	<?php
}
?>

http://example.com/print_params.php?name=Marty+Stepp&sid=1234567

• or call print_r or var_dump on $_REQUEST for debugging