User Interaction and Forms

User Interaction and Forms

For many applications of PHP, the ability to interact with users who view the

Web page is essential. Veterans of JavaScript tend to think in terms of event

handlers, which let you react directly to the actions of the user — for example,

the movement of the mouse over a link on the page. Server-side scripting languages

such as PHP have a more limited scope when it comes to user interaction. As

PHP code is activated when a page is requested from the server, user interaction

can occur only in a back-and-forth fashion: the user sends requests to the server,

and the server replies with dynamically generated pages.

The key to creating interactivity with PHP is to understand the techniques we

can use to send information about a user's interaction along with his or her request

for a new Web page. PHP makes this fairly easy, as we'll now see.

The simplest method we can use to send information along with a page request

uses the URL query string. If you've ever seen a URL with a question mark following

the file name, you've witnessed this technique in use. Let's look at an easy

example. Create a regular HTML file called welcome1.html (no .php file extension

is required, since there will be no PHP code in this file) and insert this link:

<a href="welcome1.php?name=Kevin">Hi, I'm Kevin!</a>

This is a link to a file called welcome1.php, but as well as linking to the file, we're

also passing a variable along with the page request. The variable is passed as part

of the query string, which is the portion of the URL that follows the question

mark. The variable is called name and its value is Kevin. To restate, we have created

a link that loads welcome1.php, and informs the PHP code contained in the

file that name equals Kevin.

User Interaction and Forms

To really understand the results of this process, we need to look at welcome1.php.

Create it as a new HTML file, but this time note the .php extension — this tells

the Web server that it can expect to interpret some PHP code in the file. In the

body of this new file, type:

<?php

$name = $_GET['name'];

echo( "Welcome to our Website, $name!" );

Now, if you use the link in the first file to load this second file, you'll see that

the page says "Welcome to our Website, Kevin!"

PHP automatically creates an array variable called $_GET1 that contains any values

passed in the query string. $_GET is an associative array, so the value of the name

variable passed in the query string can be accessed as $_GET['name']. Our script

assigns this value to an ordinary PHP variable ($name) and then displays it as

part of a text string using the echo function.