Scroll to selected item in Flex 4 Spark List component

Question

I\'m setting selected element in s:List component with Actionscript, it works, but List doesn\'t scroll to selected item -- need to scroll with scrollbar or mouse. Is it pos

Answer 1

I recently accomplished this in one of my projects by having a defined size for my items in the group..

<s:Scroller x="940" y="0" maxHeight="465" maxWidth="940" horizontalScrollPolicy="off" verticalScrollPolicy="off">
  <s:HGroup  id="tutPane" columnWidth="940" variableColumnWidth="false" gap="0" x="0" y="0">
  </s:HGroup>
</s:Scroller>

Following this my button controls for manipulation worked by incrementing a private "targetindex" variable, then I called a checkAnimation function, which used the Animate class, in combo with a SimpleMotionPath and a comparison between tutpane.firstIndexInView and target index. This modified the "horizontalScrollPosition" of the group.

This allowed separate controls to essentially act as a scroll bar, but I had the requirement of sliding the control to view the selected item.. I believe this technique could work for automated selection of items as well

Answer 2

I saw this basic idea here... http://arthurnn.com/blog/2011/01/12/coverflow-layout-for-flex-4/

public function scrollGroup( n : int ) : void
{
    var scrollPoint : Point = theList.layout.getScrollPositionDeltaToElement( n );
    var duration : Number = ( Math.max( scrollPoint.x, theList.layout.target.horizontalScrollPosition ) - Math.min( scrollPoint.x, theList.layout.target.horizontalScrollPosition )) * .01;
    Tweener.addTween(theList.layout,{ horizontalScrollPosition: scrollPoint.x , time:duration});
}
protected function theList_caretChangeHandler(event:IndexChangeEvent):void
{
    scrollGroup( event.newIndex );
    event.target.invalidateDisplayList();
}

Answer 3

Try the s:List method ensureIndexIsVisible(index:int):void.

Answer 4

This function will scroll to the top of the list in Flex 4+. It takes in account the height of the item, so it will work for lists with different items with different height.

private function scrollToIndex(list:List,index:int):void
{
    if (!list.layout)
        return;

    var dataGroup:DataGroup = list.dataGroup;

    var spDelta:Point = dataGroup.layout.getScrollPositionDeltaToElement(index);

    if (spDelta)
    {
        dataGroup.horizontalScrollPosition += spDelta.x;
        //move it to the top if the list has enough items
        if(spDelta.y > 0)
        {
            var maxVSP:Number = dataGroup.contentHeight - dataGroup.height;
            var itemBounds:Rectangle = list.layout.getElementBounds(index);
            var newHeight:Number = dataGroup.verticalScrollPosition + spDelta.y 
            + dataGroup.height - itemBounds.height;
            dataGroup.verticalScrollPosition = Math.min(maxVSP, newHeight);
        }
        else
        {
            dataGroup.verticalScrollPosition += spDelta.y;

        }
    }
}

Answer 5

You can multiply the height of an element by its index and pass this value to:

yourListID.scroller.viewport.verticalScrollPosition

Answer 6

For Spark:

list.ensureIndexIsVisible(index);