Creating an animated transition when scrolling through items in a Spark HGroup container in Flex 4

The following example shows how you can create a simple horizontal list using a HGroup container and do an animated scroll using the Animate and SimpleMotionPath classes and the getHorizontalScrollPositionDelta() method

Full code after the jump.

The following example(s) require Flash Player 10 and the Adobe Flex 4 SDK. To download the Adobe Flash Builder 4 trial, see www.adobe.com/products/flex/. To download the latest nightly build of the Flex 4 SDK, see opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.

For more information on getting started with Flex 4 and Flash Builder 4, see the official Adobe Flex Team blog.

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2009/11/11/creating-an-animated-transition-when-scrolling-through-items-in-a-spark-hgroup-container/ -->
<s:Application name="Spark_HGroup_horizontalScrollPosition_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark" 
        xmlns:mx="library://ns.adobe.com/flex/halo">
 
    <fx:Script>
        <![CDATA[
            import spark.core.NavigationUnit;
 
            protected function scrollToThere(dir:uint):void {
                var value:Number = hGr.getHorizontalScrollPositionDelta(dir);
                if (value != 0) {
                    pth.valueBy = value;
                    anim.play();
                }
            }
        ]]>
    </fx:Script>
 
    <fx:Declarations>
        <s:Animate id="anim" target="{hGr}" duration="500">
            <s:motionPaths>
                <s:SimpleMotionPath id="pth" property="horizontalScrollPosition" />
            </s:motionPaths>
        </s:Animate>
    </fx:Declarations>
 
    <s:Panel title="HGroup horizontalScrollPosition test"
            horizontalCenter="0" verticalCenter="0">
        <s:layout>
            <s:HorizontalLayout verticalAlign="middle" />
        </s:layout>
        <s:Button label="&lt;"
                click="scrollToThere(NavigationUnit.PAGE_LEFT);"
                width="30" />
        <s:HGroup id="hGr"
                requestedColumnCount="3"
                columnWidth="100"
                variableColumnWidth="false"
                height="100"
                clipAndEnableScrolling="true">
            <s:Label text="One" backgroundColor="red" backgroundAlpha="0.1" height="100%" />
            <s:Label text="Two" backgroundColor="red" backgroundAlpha="0.2" height="100%" />
            <s:Label text="Three" backgroundColor="red" backgroundAlpha="0.3" height="100%" />
            <s:Label text="Four" backgroundColor="red" backgroundAlpha="0.4" height="100%" />
            <s:Label text="Five" backgroundColor="red" backgroundAlpha="0.5" height="100%" />
            <s:Label text="Six" backgroundColor="red" backgroundAlpha="0.6" height="100%" />
            <s:Label text="Seven" backgroundColor="red" backgroundAlpha="0.7" height="100%" />
            <s:Label text="Eight" backgroundColor="red" backgroundAlpha="0.8" height="100%" />
            <s:Label text="Nine" backgroundColor="red" backgroundAlpha="0.9" height="100%" />
            <s:Label text="Ten" backgroundColor="red" backgroundAlpha="1.0" height="100%" />
        </s:HGroup>
        <s:Button label="&gt;"
                click="scrollToThere(NavigationUnit.PAGE_RIGHT);"
                width="30" />
    </s:Panel>
 
</s:Application>

This entry is based on a beta version of the Flex 4 SDK and therefore is very likely to change as development of the Flex SDK continues. The API can (and will) change causing examples to possibly not compile in newer versions of the Flex 4 SDK.

8 thoughts on “Creating an animated transition when scrolling through items in a Spark HGroup container in Flex 4

  1. I did this, and it works:

    protected function scrollToThere(dir:uint):void {
    var value:Number = hGr.getHorizontalScrollPositionDelta(dir);
    if (value != 0) {
    pth.valueBy = value;
    anim.play();
    }
    else
    {
    if(dir == NavigationUnit.PAGE_RIGHT)
    {
    value = hGr.getHorizontalScrollPositionDelta(NavigationUnit.HOME);
    pth.valueBy = value;
    anim.play();
    }
    if(dir == NavigationUnit.PAGE_LEFT)
    {
    value = hGr.getHorizontalScrollPositionDelta(NavigationUnit.END);
    pth.valueBy = value;
    anim.play();
    }
    }
    }

    but I was looking for a more continuous effect where it keeps going in the same direction.

  2. hmm.. how to make this animation play when mouse over on right or left items to right or left direction?
    or mousewheel scrolling this items?

  3. Hi,
    how to use a scrollbar to change the index?
    Lets say you have 99 pages and want to quickly jump to page 88.. :)
    With this above you have to press 88 Times the Arrow.

    How would I directly jump to a specific index ? How do I get the delta ?

  4. @Steve
    Yes, I just preformed a similar task to a list, for a list you must use list.layout to use the “getHorizontalScrollPosition” function and animation to work… This means the layout must be bindable.. which was a bit tricky to do… I just made the layout itself a bindable veriable, and made the lists layout = the bindable layout at creationcomplete.

    hope this helps

  5. Thanks the article.
    Btw, I am working with List on Flex Mobile. You can set clipAndEnableScrolling in HorizontalLayout of List and work with this instead of List

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