Creating an XML Gallery with ActionScript 3.0

Paul — Thu, 15 May 2008 02:37:28 +0000

For any dynamic Flash project, XML will be a powerful tool. One of the most common examples (and one of the simplest) is a picture gallery like the one I have here:

Images came from http://www.stockvault.net/

I will be talking about how to use Flash and XML to make a simple, yet superfly, gallery.

So, let us start off by looking at my XML file’s structure:

dir="//url/Photos/">
id=‘0′ file="photo_7030_20070301.jpg" width=‘500′ height=‘375′>
Cute Puppy! Who couldn’t love that face?
>
id=‘1′ file="photo_4095_20070301.jpg" width=‘500′ height=‘375′>
Three Friendly Cats.
>
id=‘2′ file="photo_4281_20070301.jpg" width=‘500′ height=‘375′>
The Terror of the UnderSofa!
>
id=‘3′ file="photo_6257_20070301.jpg" width=‘500′ height=‘375′>
Bored? Let’s play catch!
>
id=‘4′ file="photo_6882_20070301.jpg" width=‘500′ height=‘377′>
It may be natural, but this picture still feels weird to me.
>
id=‘5′ file="photo_7241_20070301.jpg" width=‘500′ height=‘375′>
My cats hate the snow.
>
id=‘6′ file="photo_7538_20070507.jpg" width=‘500′ height=‘622′>
LOOK IT'S HTML!!!]]>
>
id=‘7′ file="photo_7915_20070609.jpg" width=‘500′ height=‘371′>
Skinny cats are OK too.
>
>

XML is very simple to understand if you know anything about HTML’s tag structure. The XML document has a root tag that has an attribute dir=”//url/Photos/”. Every tag has to be closed within it’s own level of the tree. Our gallery tag is closed at the bottom of the document with . This means that all the tags are elements inside the gallery element (both open and close tags combined make up an element).

Our tags have several attributes, such as the images file name and it’s pixel demensions. Inside each element we have a short comment about the image that will be displayed in a TextField in our Flash movie.

One important thing to notice here is that if you want to have HTML in your TextField then you need to tell the code that something is a string containing HTML and not more elements. We do this with a special bracket HTML GOES HERE ]]> Isn’t that GREAT! That right there probably made this whole tutorial worth while (that was a problem that took me a long time to solve).

OK, now that we’ve looked at the XML we need to make it work with ActionScript 3. In Adobe Flash CS3 I created a new AS3 FLA doc and a new AS doc. In the FLA I simply created some very basic MovieClips for my left and right arrows and I placed a TextField at the bottom of my stage (which I set to 600 X 700 with a black background). After naming my instances and setting up the Document Class linkage I was done with the FLA side of thing and the rest is ActionScript.

Our Document Class has to extend MovieClip so we take our first steps thusly:

public class Main extends MovieClip {
public var currentImg:Number;
public var lastImg:Number;
public var xml:XML;
public var loader:Loader;
public var xmlLoader:URLLoader;

public function Main() {
loader = new Loader();
addChild(loader);

xmlLoader = new URLLoader(new URLRequest("//url/gallery.xml"));
xmlLoader.addEventListener(Event.COMPLETE, parseXML);

left_mc.stop(); //Need to stop the arrows from flickering
right_mc.stop();
}
}

In our constructor we are initializing our Loader which will contain the loaded images and we are loading our XML document. When the XML doc is done loading, the function parseXML will handle the content.

protected function parseXML(event:Event):void {
left_mc.addEventListener(MouseEvent.MOUSE_UP, nextImg);
left_mc.addEventListener(MouseEvent.MOUSE_OUT, arrowOut);
left_mc.addEventListener(MouseEvent.MOUSE_OVER, arrowOver);
right_mc.addEventListener(MouseEvent.MOUSE_UP, prevImg);
right_mc.addEventListener(MouseEvent.MOUSE_OUT, arrowOut);
right_mc.addEventListener(MouseEvent.MOUSE_OVER, arrowOver);

xml = new XML(event.currentTarget.data);
lastImg = xml.img.length() – 1;
currentImg = 0;
loadImg();
}

I’ve recently gotten into the habit of using protected functions rather then private functions. There is only one difference between the two and that’s that private anything won’t be inherited by child classes.
In this function I set the MouseEvents for the arrows because if the XML failed to load, there would be no reason for the arrows to work.

Alright, so I saved my XML tree in the var xml for ease of use later. I also saved the number of images in my XML doc using the length() method. Something to know about the length method is it will only tell you how many elements there are of that tag type at that level. For example, if I were to have child elements inside my img elements that would not affect the return value of xml.img.length(); It’s only telling you how many img elements are children of gallery (gallery is accessed with the var xml directly).

protected function loadImg():void {
loader.x = (stage.width – Number(xml.img[currentImg].@width))/2;
loader.y = (stage.height – 50 – Number(xml.img[currentImg].@height))/2;
loader.load(new URLRequest(xml.@dir + xml.img[currentImg].@file));
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadFin);
}
protected function loadFin(event:Event):void {
textDisp_TF.htmlText = xml.img[currentImg];
}

In that first function I’m just going to focus on the one line with the URLRequest. In order to traverse an XML tree you need start with the base. Your XML var (in our case it’s called xml) points to that base (in this case the base is gallery). So when we want to access the attribute dir in the tag gallery, we need to type xml.@dir and this will return “//url/Photos/”. The ‘@’ symbol denotes that it’s an attribute and not an element (tag).

Getting the file name is just one step further. currentImg is a Number variable that stores which image we are on. Thinking of our XML var as something similar to a bunch of nested arrays we can see how you might access a specific file name with xml.img[currentImg].@file This says we want the file attribute in the [currentImg] (first second so forth) img element which is in our base element. There are quite a few ways of finding what you need in an XML doc and you can learn more about them here.

In the second function we are displaying the text from within our XML img element. Here we aren’t accessing any attributes or anything, this is where we get the content between the open and close tags.

Finally we have the arrow MouseEvent handlers:

protected function arrowOut(event:MouseEvent):void {
MovieClip(event.currentTarget).gotoAndStop(1);
}

protected function arrowOver(event:MouseEvent):void {
MovieClip(event.currentTarget).gotoAndStop(2);
}

protected function nextImg(event:MouseEvent):void {
loader.unload();
currentImg = (currentImg < lastImg)? currentImg + 1 : 0;
loadImg();
}

protected function prevImg(event:MouseEvent):void {
loader.unload();
currentImg = (currentImg > 0)? currentImg – 1 : lastImg;
loadImg();
}

Once again I’m using the less obvious form of the if..else statement.

if(num>5) {
num = 5;
}else {
num = 0;
}
//OR, THIS NEXT PART DOES THE SAME THING
num = (num>5)? 5 : 0;

Well that’s about it for this level of a gallery. You can make galleries look really nice with fade transitions between images, small loading animations for larger images, scrollable thumbnail selection menu… etc.

Here is a downloadable source of my example file (images not included… get them here): XMLGallery.zip

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Creating an XML Gallery with ActionScript 3.0