How to implement background images on Spark control buttons with scale 9

Hopefully this quick post will be a bit of a time saver for Flex Developers developing Flex 4 SDK projects with Flash Builder or other tools…

Over the last year or 2 I’ve really got comfortable with reskinning Flex 3 applications. For me the quickest, simlest way has usually been to cut up the designer’s photoshop file and implement Scale 9 and syntax in my Flex css files – an example of a recent Flex 3 button skin looked like this:

fontSize    : 44px;
fontWeight    : bold;
paddingLeft    : 15px;
paddingRight: 15px;

upSkin        : Embed(source=”assets/images/new/buttons/answerButtonUp.png”,scaleGridTop=”20″, scaleGridLeft=”19″, scaleGridRight=”145″,  scaleGridBottom=”99″);
overSkin    : Embed(source=”assets/images/new/buttons/answerButtonOver.png”,scaleGridTop=”20″, scaleGridLeft=”19″, scaleGridRight=”145″,  scaleGridBottom=”99″);
downSkin    : Embed(source=”assets/images/new/buttons/answerButtonOver.png”,scaleGridTop=”20″, scaleGridLeft=”19″, scaleGridRight=”145″,  scaleGridBottom=”99″);
disabledSkin: Embed(source=”assets/images/new/buttons/answerButtonUp.png”,scaleGridTop=”20″, scaleGridLeft=”19″, scaleGridRight=”145″,  scaleGridBottom=”99″);
selectedDisabledSkin: Embed(source=”assets/images/new/buttons/answerButtonUp.png”,scaleGridTop=”20″, scaleGridLeft=”19″, scaleGridRight=”145″,  scaleGridBottom=”99″);


Luckily for me the Flex 4 SDK is backwards compatible for the most part so you can still skin an mx.controls.Button component with the CSS above.

However… one of the reasons I’ve been migrating my Flex 3 project to Flex 4 is to make use of some of the skinning improvements it offers with it’s new Spark components built on top of the Flex 3 halo components.

The code above does not work on a spark.components.Button. I assumed it would… Here’s how I got the example below to work:

Step 1) Create a new Flex Project in Flash Builder

Step 2) You can still customize the label colours and states but you’ll need to implement the new namespaces in CSS introduced in Flex 4 to avoid warnings and errors – see the gumbo_scale_nine.css file.

Step 3) You’ll also notice within the gumbo_scale_nine.css file that I’m pointing a custom style (‘answerButton’) to an MXML skin file in the location com.nickkuh.skins.AnswerButtonSkin.mxml. This is the file that I’ve used to custom skin the spark button component. I copied the ButtonSkin.mxml file that comes with Flex 4, stipped out a load of fills and strokes I didn’t require and add these important lines:

<s:BitmapImage left=”0″ right=”0″ top=”0″ bottom=”0″ source=”@Embed(source=’assets/answerButtonUp.png’,scaleGridTop=’20’, scaleGridLeft=’19’, scaleGridRight=’145′,  scaleGridBottom=’99’)” resizeMode=”scale” includeIn=”up” />

<s:BitmapImage left=”0″ right=”0″ top=”0″ bottom=”0″ source=”@Embed(source=’assets/answerButtonOver.png’,scaleGridTop=’20’, scaleGridLeft=’19’, scaleGridRight=’145′,  scaleGridBottom=’99’)” resizeMode=”scale” excludeFrom=”up” />

By default the resizeMode parameter will just tile and repeat your graphic which wasn’t the desired functionality.

So that’s it. Although it took more step to reskin than a Flex 3 component I can certainly see the benefits of the separate FXG skin file. Next step is to change that SimpleText labelElement into a RichEditableText component and enable multilines and imline images into my Spark buttons. Wish me luck!