Using LoadVars for Server-Flash Communications

LoadVars

The LoadVars class, introduced in Flash MX, allows sending of data between Flash and a web server, and provides a callback mechanism for dealing with data returned from the server (asynchronously).

Sending data to the server

The steps for sending data to a serverside script (PHP, ASP, Coldfusion, JSP, etc) are:

Create an instance of the LoadVars class
Assign whatever data you want to send to a property or properties of that instance
Use the send method of the LoadVars instance to send the data

You have the choice of specifying GET (in which case the parameters you pass will be visible in the URL as an appended querystring) or POST for sending the data. Note that if you are testing from within the Flash IDE, eg for testing, you can only issue a GET -- POSTS only work when sent from Flash running in a browser.

Sending data to and receiving data from the server

To send and receive data (the more usual case, as it's good to know whether the operation succeeded or failed even if you don't want any other information from the server), the steps are:

Create two instances of the LoadVars class, one for sending data (dataout) and the other for receiving it (datain)
Assign whatever data you want to send to a property or properties of the 'dataout' instance
Assign a function to the onLoad property of the 'datain' LoadVars instance to deal with returned data
Use the sendAndLoad method of the 'dataout' LoadVars instance to send the data, specifying 'datain' as the instance that will deal with returned data

An example of LoadVars sending data from Flash to PHP

If, for example, you wanted your Flash movie to get a username and password from a site visitor and forward them to another non-Flash page at the site with an appropriate message, you could use something like this Flash form:

which contains two TextInput components named username and password (valid combos, according to the PHP script, are Fred/0001, Jane/2000, or Mary/3333) and a Button component named enterbtn and has this code in frame 1:

// create an instance of LoadVars to send data
var dataOut:LoadVars = new LoadVars();

function checkUser():Void {
   dataOut.username = username.text;
   dataOut.password = password.text;
   dataOut.send("checkuser1.php", "newwin", "POST");
}

enterbtn.addEventListener("click", checkUser);

together with this PHP script, checkuser1.php (though the more likely scenario would be to do a database lookup instead):

checkuser1.php

<?
$users = array(
   'Fred' => '0001',
   'Jane' => '2000',
   'Mary' => '3333');

$d = getdate();
$found = false;

foreach($users as $un => $pw) {
   if ($_POST['username']==$un && $_POST['password']==$pw) {
      echo 'Welcome. The time here in Washington DC is '.$d['hours'].':'.$d['minutes'];
      $found = true;
      break;
   }
}

if (!$found) {
   echo 'Sorry, you are not cleared to know what time it is now in Washington DC';
}
?>

You can see if you try the Flash form above with a username and password from the list in the PHP script, a new window will be opened with a message telling you the time, whereas if you enter anything else, the new window will display a different message. If you want the window contents to display in the same window as the one the Flash movie is embedded in, use "_self" in place of "newwin" in the send method of LoadVars.

An example of LoadVars sending data from Flash to PHP and receiving data back

Data sent from a serverside script to Flash must be sent in a specific format if it is to be read within a LoadVars onLoad routine. It must consist of variable=value pairs separated by ampersands. It's also a good idea to put an ampersand at the beginning and end of the string being sent back, to make sure nothing extraneous is added to the variable name at the beginning of the string, or to the value at the end. If the example above were reworked to display the result within the Flash movie instead of in a separate browser window, the script could return two pieces of data: an indication of whether the username/password was found, and the current time. Thus, a legitimate return string could be

"&valid=1&time=14:30&

Here is the same movie with the result displayed in the Flash movie itself instead of another browser window:

It's the same content as above, plus a TextArea component named msg. This is the code in frame 1:

// hide the message box til there is something to display
msg.setStyle("backgroundColor", 0x003399);
msg.setStyle("borderStyle", "none");
msg.setStyle("color", 0xffffff);

// create two new instances of LoadVars, one to send and one to receive data
var dataOut:LoadVars = new LoadVars();
var dataIn:LoadVars = new LoadVars();

// define what should happen when the response is received,
// using 'this' to refer to dataIn and get data from it
dataIn.onLoad = function() {
   if (this.valid=="1") {
      msg.text = 'Welcome. The time here in Washington DC is ' + this.time;
   } else {
      msg.text = 'Sorry, you are not cleared to know what time it is now in Washington DC';
   }
}

// the function that will be called by the Enter button 
function checkUser():Void {
   dataOut.username = username.text;
   dataOut.password = password.text;
   dataOut.sendAndLoad("checkuser2.php", dataIn, "POST");
}

// define the behavior of the Enter button
enterbtn.addEventListener("click", checkUser);

And this is the PHP script (checkuser2.php):

checkuser2.php

<?
$users = array(
      'Fred' => '0001',
      'Jane' => '2000',
      'Mary' => '3333');

$d = getdate();
$found = false;

foreach($users as $un => $pw) {
	if ($_POST['username']==$un && $_POST['password']==$pw) {
		echo '&valid=1&time='.$d['hours'].':'.$d['minutes'].'&';
		$found = true;
		break;
	}
}

if (!$found) echo '&valid=0&';
?>

Notice that the only difference between checkuser2.php and checkuser1.php above is the echo string. In checkuser1.php, where the output is destined for the browser window, the echoed string is formatted for display. In checkuser2.php, where the output is destined for Flash, the echo string is made up of variable=value pairs, surrounded by &s. Flash itself will format this returned data for display, within the LoadVars onLoad routine.