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

By Peter deHaan On November 11, 2009 · 8 Comments

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 http://www.adobe.com/products/flex/. To download the latest nightly build of the Flex 4 SDK, see http://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.

About The Author

Peter deHaan

Peter deHaan currently works for Adobe on the Flex SDK QA team. While not working on Flex, Flash, and ColdFusion applications, Peter enjoys making up bios and writing in 3rd person. Peter's rarely updated blog can be found at blogs.adobe.com/pdehaan/, actionscriptexamples.com, airexamples.com, and coldfusionexamples.com.

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

Paolo says:

November 11, 2009 at 1:33 pm

Very nice, this is something I was looking for. Is there a way to loop to the beginning once you reach the end?

Reply
Paolo says:

November 11, 2009 at 1:49 pm

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.

Reply
MechanisM says:

November 12, 2009 at 7:05 pm

Very nice done!! Thanxx!!

Reply
MechanisM says:

November 12, 2009 at 7:13 pm

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?

Reply
Steve says:

November 22, 2009 at 9:09 am

Can you do something similar with an entity that can have data bound to it, like a List?

Reply
innur says:

March 3, 2010 at 3:28 am

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 ?

Reply
loogie says:

November 2, 2010 at 6:59 am

@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

Reply
Quyen says:

January 5, 2011 at 8:04 pm

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

Reply