Create skins for a mobile application

When customizing mobile skins, you create a custom mobile skin class. In some cases, you also edit the assets that a mobile skin class uses.

When you edit a mobile skin class, you can change state-based interactions, implement support for new styles, or add or remove child components to the skin. You typically start with the source code of an existing skin and save it as a new class.

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You can also edit the assets used by mobile skins to change the visual properties of the skin, such as size, color, or gradients and backgrounds. In this case, you also edit the FXG assets used by the skins. The source *.fxg files used by mobile skins are located in the spark/skins/mobile/assets directory.

Not all visual properties for mobile skins are defined in *.fxg files. For example, the Button skin’s background color is defined by the chromeColor style property in the ButtonSkin class. It is not defined in an FXG asset. In this case, you would edit the skin class to change the background color.

Create a mobile skin class

When creating a custom mobile skin class, the easiest approach is to use an existing mobile skin class as a base. Then change that class and use it as a custom skin.

To create a custom skin class:
  1. Create a directory in your project (for example, customSkins). This directory is the package name for your custom skins. While creating a package is not required, it’s a good idea to organize custom skins in a separate package.

  2. Create a custom skin class in the new directory. Name the new class whatever you want, such as

  3. Copy the contents of the skin class that you are using as a base for the new class. For example, if you are using ButtonSkin as a base class, copy the contents of the file into the new custom skin class.

  4. Edit the new class. For example, make the following minimum changes to the CustomButtonSkin class:
    • Change the package location:
      package customSkins 
      //was: package
    • Change the name of the class in the class declaration. Also, extend the class your new skin is based on, not the base skin class:
      public class CustomButtonSkin extends ButtonSkin 
      // was: public class ButtonSkin extends ButtonSkinBase
    • Change the class name in the constructor:
      public function CustomButtonSkin() 
      //was: public function ButtonSkin()
  5. Change the custom skin class. For example, add support for additional states or new child components. Also, some graphical assets are defined in the skin class itself, so you can change some assets.

    To make your skin class easier to read, you typically remove any methods from the custom skin that you do not override.

    The following custom skin class extends ButtonSkin and replaces the drawBackground() method with custom logic. It replaces the linear gradient with a radial gradient for the background fill.
    package customSkins {   
        import mx.utils.ColorUtil;
        import flash.display.GradientType;
        import flash.geom.Matrix;
        public class CustomButtonSkin extends ButtonSkin {
            public function CustomButtonSkin() {
            private static var colorMatrix:Matrix = new Matrix();
            private static const CHROME_COLOR_ALPHAS:Array = [1, 1];
            private static const CHROME_COLOR_RATIOS:Array = [0, 127.5];        
            override protected function drawBackground(unscaledWidth:Number, unscaledHeight:Number):void {
                super.drawBackground(unscaledWidth, unscaledHeight);        
                var chromeColor:uint = getStyle("chromeColor");
                if (currentState == "down") {
                } else {            
                var colors:Array = [];
                colorMatrix.createGradientBox(unscaledWidth, unscaledHeight, Math.PI / 2, 0, 0);
                colors[0] = ColorUtil.adjustBrightness2(chromeColor, 70);
                colors[1] = chromeColor;    
                graphics.beginGradientFill(GradientType.RADIAL, colors, CHROME_COLOR_ALPHAS, CHROME_COLOR_RATIOS, colorMatrix);
                // }            
                graphics.drawRoundRect(layoutBorderSize, layoutBorderSize, 
                    unscaledWidth - (layoutBorderSize * 2), 
                    unscaledHeight - (layoutBorderSize * 2), 
                    layoutCornerEllipseSize, layoutCornerEllipseSize);
  6. In your application, apply the custom skin by using one of the methods that are described in Apply a custom mobile skin. The following example uses the skinClass property on the component tag to apply the customSkins.CustomButtonSkin skin:

    <?xml version="1.0" encoding="utf-8"?>
    <!-- mobile_skins/views/CustomButtonSkinView.mxml -->
    <s:View xmlns:fx="" 
        xmlns:s="library://" title="Home">
            <!-- Place non-visual elements (e.g., services, value objects) here -->
        <s:Button label="Click Me" skinClass="customSkins.CustomButtonSkin"/>

Lifecycle methods of mobile skins

When creating custom skin classes, familiarize yourself with the following UIComponent methods. These inherited, protected methods define a skin’s children and members, as well as help it interact with other components on the display list.
  • createChildren() — Create any child graphics or text objects needed by the skin.

  • commitProperties() — Copy component data into the skin, if necessary.

  • measure() — Measure the skin, as efficiently as possible, and store the results in the measuredWidth and measuredHeight properties of the skin.

  • updateDisplayList() — Set the position and size of graphics and text. Do any ActionScript drawing required. This method calls the drawBackground() and layoutContents() methods on the skin.

For more information about using these methods, see Implementing the component .

Common methods to customize in mobile skins

Many mobile skins implement the following methods:
  • layoutContents() — Positions the children for the skin, such as dropshadows and labels. Mobile skin classes do not support Spark layouts such as HorizontalLayout and VerticalLayout. Lay out the skin’s children manually in a method such as layoutContents().

  • drawBackground() — Renders a background for the skin. Typical uses include drawing chromeColor, backgroundColor or contentBackgroundColor styles based on the shape of the skin. Can also be used for tinting, such as with the applyColorTransform() method.

  • commitCurrentState() — Defines state behaviors for mobile skins. You can add or remove supported states, or change the behavior of existing states by editing this method. This method is called when the state changes. Most skin classes override this method. For more information, see Mobile skin states.

Create custom FXG assets

Most visual assets of mobile skins are defined using FXG. FXG is a declarative syntax for defining static graphics. You can use a graphics tool such as Adobe Fireworks, Adobe Illustrator, or Adobe Catalyst to export an FXG document. Then you can use the FXG document in your mobile skin. You can also create FXG documents in a text editor, although complex graphics can be difficult to write from scratch.

Mobile skins typically use FXG files to define states of a skin. For example, the CheckBoxSkin class uses the following FXG files to define the appearance of its box and checkmark symbol:
  • CheckBox_down.fxg

  • CheckBox_downSymbol.fxg

  • CheckBox_downSymbolSelected.fxg

  • CheckBox_up.fxg

  • CheckBox_upSymbol.fxg

  • CheckBox_upSymbolSelected.fxg

If you open these files in a graphics editor, they appear as follows:

Checkbox states (down, downSymbol, downSymbolSelected, up, upSymbol, and upSymbolSelected)

FXG files for multiple resolutions

Most mobile skins have three sets of FXG graphics files, one for each default target resolution. For example, different versions of all six CheckBoxSkin classes appear in the spark/skins/mobile160, spark/skins/mobile240, and spark/skins/mobile320 directories.

When you create a custom skin, you can do one of the following:
  • Use one of default skins as a base (usually 160 DPI). Add logic that scales the custom skin to fit the device the application is running on by setting the applicationDPI property on the Application object.

  • Create all three versions of the custom skin (160, 240, and 320 DPI) for optimal display.

Some mobile skins use a single set of FXG files for their graphical assets and do not have DPI-specific graphics. These assets are stored in the spark/skins/mobile/assets directory. For example, the ViewMenuItem skins and TabbedViewNavigator button bar skins do not have DPI-specific versions, so all of their FXG assets are stored in this directory.

Customize FXG file

You can open an existing FXG file and customize it, or create one and export it from a graphics editor such as Adobe Illustrator. After you edit the FXG file, apply it to your skin class.

To create a custom skin by modifying an FXG file:
  1. Create a custom skin class and put it in the customSkins directory, as described in Create a mobile skin class.

  2. Create a subdirectory under the customSkins directory; for example, assets. Creating a subdirectory is optional, but helps to organize your FXG files and skin classes.

  3. Create a file in the assets directory and copy the contents of an existing FXG file into it. For example, create a file named CustomCheckBox_upSymbol.fxg. Copy the contents of the spark/skins/mobile160/assets/CheckBox_upSymbol.fxg into the new CustomCheckBox_upSymbol.fxg file.

  4. Change the new FXG file. For example, replace the logic that draws a check with an “X” filled with gradient entries:
    <?xml version='1.0' encoding='UTF-8'?>
    <!-- mobile_skins/customSkins/assets/CustomCheckBox_upSymbol.fxg -->
    <Graphic xmlns="" version="2.0"
        viewWidth="32" viewHeight="32">
        <!-- Main Outer Border -->
        <Rect x="1" y="1" height="30" width="30" radiusX="2" radiusY="2">
                <SolidColorStroke weight="1" color="#282828"/>
        <!-- Replace check mark with an "x" -->
        <Group x="2" y="2">
            <Line xFrom="3" yFrom="3" xTo="25" yTo="25">
                    <LinearGradientStroke caps="none" weight="8" joints="miter" miterLimit="4">
                        <GradientEntry color="#FF0033"/>
                        <GradientEntry color="#0066FF"/>
            <Line xFrom="25" yFrom="3" xTo="3" yTo="25">
                    <LinearGradientStroke caps="none" weight="8" joints="miter" miterLimit="4">
                        <GradientEntry color="#FF0033"/>
                        <GradientEntry color="#0066FF"/>
  5. In the custom skin class, import the new FXG class and apply it to a property. For example, in the CustomCheckBox class:
    1. Import the new FXG file:
      import customSkins.assets.CustomCheckBox_upSymbol;
    2. Add the new asset to the custom skin class. For example, change the value of the upSymbolIconClass property to point to your new FXG asset:
      upSymbolIconClass = CustomCheckBox_upSymbol;

The complete custom skin class looks like the following:

// mobile_skins/customSkins/ 
package customSkins {   
    import customSkins.assets.CustomCheckBox_upSymbol; 
    public class CustomCheckBoxSkin extends CheckBoxSkin { 
        public function CustomCheckBoxSkin() { 
            upSymbolIconClass = CustomCheckBox_upSymbol; // was CheckBox_upSymbol 

For information about working with and optimizing FXG assets for skins, see Optimizing FXG.

View FXG files in applications

Because FXG files are written in XML, it can be difficult to visualize what the final product looks like. You can write a Flex application that imports and renders FXG files by adding them as components and wrapping them in a Spark container.

To add FXG files as components to your application, add the location of the source files to your application’s source path. For example, to show mobile FXG assets in a web-based application, add the mobile theme to your source path. Then the compiler can find the FXG files.

The following desktop example renders the various FXG assets of the CheckBox component when you use it in a mobile application. Add the frameworks\projects\mobiletheme\src\ directory to the compiler’s source-path argument when you compile this example.
<?xml version="1.0"?>
<!-- mobile_skins/ShowCheckBoxSkins.mxml -->
<s:Application xmlns:fx="" 
    NOTE: You must add the mobile theme directory to source path 
    to compile this example.
    For example: 
    mxmlc -source-path+=\frameworks\projects\mobiletheme\src\ ShowCheckBoxSkins.mxml

    <s:Label text="160 DPI" fontSize="24" fontWeight="bold"/>

    <mx:Spacer height="30"/>

    <s:Label text="240 DPI" fontSize="24" fontWeight="bold"/>

    <mx:Spacer height="30"/>

    <s:Label text="320 DPI" fontSize="24" fontWeight="bold"/>

    <s:Label text="down, downSymbol, downSymbolSelected, up, upSymbol, upSymbolSelected"/>


Use text in custom mobile skins

To render text in mobile skins, you use the StyleableStageText or StyleableTextField class. These text classes are optimized for mobile applications.

StyleableStageText provides access to the native text inputs for the TextInput and TextArea controls. It extends the UIComponent class, and implements the IEditableText and ISoftKeyboardHintClient interfaces.

StyleableTextField is also used by the TextInput and TextArea controls when you do not want access to the native inputs. It is also used by non-input text controls such as ActionBar and Button. It extends the TextField class, and implements the ISimpleStyleClient and IEditableText interfaces.

For more information about using text controls in mobile applications, see Use text in a mobile application.

TLF in mobile skins

For performance reasons, try to avoid classes that use TLF in mobile skins. In some cases, such as with the Spark Label component, you can use classes that use FTE.

htmlText in mobile skins

You cannot use the htmlText property in mobile applications.

Gestures with text

Touch+drag gestures always select text (when text is selectable or editable). If the text is inside a Scroller, the Scroller only scrolls if the gesture is outside the text component. These gestures only work when the text is editable and selectable.

Make text editable and selectable

To make the text editable and selectable, set the editable and selectable properties to true:
textDisplay.editable = true; 
textDisplay.selectable = true;


Bi-directionality is not supported for text in the StyleableStageText or StyleableTextField class.