To expand on Peter's response:
Like Peter said, you create all the elements you need when the item renderer is
first created. If you don't want to show a button, set the visibility to false
and depending on how you are laying them out, you might need to set the size to
0 as well. That way you can simulate them being added and removed and have
things reflow properly. You'll have to set gap to 0 and you might need to play
around with spacers as well for this to work.
HTH,
Harbs
On Sep 3, 2013, at 4:40 PM, Peter Ent wrote:
> Each time the itemRenderer's data is set, you are wiping out all of the
> button in the TileGroup and re-creating them. That's a source of your slow
> scrolling performance.
>
> As nice-and-easy as your approach is, it is better to add some more code
> complexity and re-use those buttons.
>
> Here's one example: you could, for each itemRenderer, have a cache of
> previously created buttons, which would be empty the first time the
> itemRenderer was used. If you need 10 buttons but have less than 10 (e.g.,
> 0 the first time), "use" the buttons (explained below) you have previously
> created and create the remaining, being sure to also put references to
> them into your cache.
>
> If you have more buttons in your cache than you need, "use" the amount you
> need and "deactivate" the ones you don't. That is, if you have 20 buttons
> in the cache but only need 8, you'll deactivate the remaining 12.
>
> So "use" means to set a button's visible and includeInLayout properties to
> true. "Deactivate" means to set a button's visible and includeInLayout
> properties to false.
>
> I think an approach like this would have better performance for you. If
> you can avoid setting includeInLayout, it will be even better since all
> you will be doing is hiding/showing the buttons, but the itemRenederers
> might not look right if you also don't remove them from the layout.
>
> Peter Ent
> Flex SDK Team
> Adobe Systems
>
> On 9/3/13 9:29 AM, "Federico De Maddalena" <f.demaddal...@patente.it>
> wrote:
>
>> Hi Ben
>> I'm developing a mobile project, not desktop!
>> Images in use are very small.
>> Usevirtuallayout is set on true.
>> The code is here:
>>
>> <fx:Script>
>> <![CDATA[
>> import spark.components.Button;
>> import spark.core.ContentCache;
>>
>> import events.SchedaEvent;
>>
>> static public const s_imageCache:ContentCache=new
>> ContentCache();
>>
>> override public function set data(value:Object):void
>> {
>> super.data=value;
>> lezione.text=value.titolo;
>> img.source="img/lez/"+value.lezione+"g.png";
>>
>> schede.removeAllElements();
>> for(var i:int=0; i<value.schede.length; i++)
>> {
>> var button:Button=new Button();
>> button.label=String(i+1);
>> button.id=value.schede[i];
>> button.height=40;
>> button.width=40;
>>
>> button.addEventListener(MouseEvent.CLICK, handleMouseClick);
>> schede.addElement(button);
>> }
>> }
>>
>> private function handleMouseClick(event:MouseEvent):void
>> {
>> sendEvent(parseInt(event.currentTarget.id));
>> }
>>
>> private function sendEvent(id:int):void
>> {
>> var e:SchedaEvent=new
>> SchedaEvent(SchedaEvent.LOAD_SCHEDA);
>> e.Id=id;
>>
>> this.owner.dispatchEvent(e);
>> }
>> ]]>
>> </fx:Script>
>>
>> <s:HGroup width="100%" height="100%" paddingTop="3">
>> <s:VGroup height="100%" width="20%" verticalAlign="top"
>> horizontalAlign="center">
>> <s:Image width="80%" height="80%" id="img"
>> contentLoader="{s_imageCache}"/>
>> </s:VGroup>
>> <s:VGroup height="100%" width="70%">
>> <s:Label width="100%" height="20%" id="lezione"/>
>> <s:TileGroup width="100%" height="80%" id="schede"/>
>> </s:VGroup>
>>
>> </s:HGroup>
>>
>> -----Messaggio originale-----
>> Da: Ben Smeets [mailto:b...@okapion.com]
>> Inviato: martedì 3 settembre 2013 15.22
>> A: users@flex.apache.org
>> Oggetto: Re: Improve spark List performance
>>
>> How many rows in the list? (i.c.w. useVirtualLayout)
>>
>> The setup you mention shouldn't be a problem I think (unless the image
>> you talk about is 200MB a pop), but depends on the implementation
>> (details). E.g., if the buttons are created every scroll, instead of
>> reused, that might be a cause.
>>
>> Any code you can share, can help (me at least) to track down the culprit.
>>
>> Not a guru here though, so maybe others will know off the top of their
>> heads :)
>>
>> Ben
>>
>> P.S. We are talking desktop app here right? Mobile is a different beast
>> all together (for me).
>>
>>
>>
>> On 3 sep. 2013, at 15:16, Federico De Maddalena
>> <f.demaddal...@patente.it> wrote:
>>
>>> Hi! I'm working on a mobile project.
>>> I created a spark List, which item renderer is an extension of
>>> ItemRenderer. Each of my item renderer contains one spark Image, one
>>> Label and a number of small buttons which varies from 3 to 20.
>>> Now, scrolling the list is terribly slow. There are ways to improve
>>> scroll speed? I spent a lot of time but without success.
>>> Regards
>>> federico
>>>
>>
>
