<mx:DataGrid dataProvider="{yourCollection}>
<mx:columns>
<mx:DataGridColumn dataField="yourBooleanField"
itemRenderer="mx.controls.CheckBox" editable="true"/>
</mx:columns>
</mx:DataGrid>
Fill up the yourCollection with a bunch of objects or xml with a field
named yourBooleanField. Run it and they will initially display fine.
Select some, unselect others. Scroll them off the page the scroll
them back into view and their state will not be kept.
I posted a question about that and Tracy set me straight with an
example (I tweeked it a bit as I needed and is the renderer in my post
here). He gave me a couple links about why I had to write a checkbox
renderer for it to remember state.
I'll look into the option given by the other response to this tread.
Thanks,
Dale
--- In flexcoders@yahoogroups.com, leds usop <[EMAIL PROTECTED]> wrote:
>
> im just wondering why you think an ordinary check box wont retain
it's selected state when scrolling? can you provide an example code
that does that? maybe it will be more beneficial to approach the
problem using that approach. Just a thought.
>
>
> --- On Sun, 5/25/08, dbronk [EMAIL PROTECTED] wrote:
> From: dbronk [EMAIL PROTECTED]
> Subject: [flexcoders] Why is this renderer so slow?
> To: flexcoders@yahoogroups.com
> Date: Sunday, May 25, 2008, 12:59 AM
>
> I have created a checkbox renderer. My datagrid has 5 out of 8
> columns that use it. The datagrid has only about 80 rows it it. When
> using this renderer the performance of the datagrid is horrible.
> Scrolling is extremely slow, click a checkbox is extremely slow. If I
> swap out and use a normal mx:CheckBox for the renderer the performance
> is just fine, but of course that doesn't work as it will not retain
> the state of the checkbox when scrolling. Here is my code for the
> renderer. I notice that many of these are re-executed whenever
> anything happens to the datagrid. That includes just mousing over.
>
> Thanks.
>
> Dale
>
> package renderer
> {
> import flash.events. MouseEvent;
>
> import mx.controls. CheckBox;
>
> import spectrumk12. minerva.util. BaseEvent;
> import spectrumk12. minerva.util. Utils;
>
> [Event(name= "selectionSet" , type="util.BaseEven t")]
> public class RendererCheckBoxXML extends CheckBox
> {
> private var _xmlItem : XML; //holds the current item xml node
> private var count:int=0;
> private var debug:String= "";
>
> /** The attribute in the xml to use to store the selected state
> of
> this checkbox. */
> [Inspectable( default=" rendererSelected ")]
> public var selectedAttribute : String = "rendererSelected" ;
>
> /** The default selection state (true/false) to give if the
> selectedAttribute is not there or null */
> [Inspectable( default=" false", enumeration= "true,false" )]
> public var defaultSelectedStat e : Boolean = false;
>
> public function RendererCheckBoxXML ()
> {
> super();
> trace("RendererChec kBoxXML:Construc tor");
> this.addEventListen er(MouseEvent. CLICK, onClick,
> false, 0, true);
> }
>
> // Sets the state of the checkbox based on the selectedAttribute
> attribute.
> override public function set data(oItem:Object) : void
> {
> _xmlItem = XML(oItem);
> trace("RendererChec kBoxXML:set data: " + [EMAIL
> PROTECTED]) ;
> var bSelected : Boolean = false;
> var attrSelected : String = [EMAIL PROTECTED]
> Attribute] ;
> this.selected = ( Utils.nullOrBlank( attrSelected) ?
> defaultSelectedStat e : (attrSelected == "true") );
> }
>
> override public function get data() : Object
> {
> trace("RendererChec kBoxXML:get data: " + (_xmlItem !=
> null ?
> [EMAIL PROTECTED] : "null"));
> return _xmlItem;
> }
>
> /**
> * This overridden function is where the logic is for updating
the xml.
> */
> override public function set selected(selectedFl ag:Boolean) :
> void
> {
> trace("RendererChec kBoxXML:set selected: " + [EMAIL
> PROTECTED]) ;
> super.selected = selectedFlag;
>
> // Only update the xml if it needs to be updated. Each
> time the xml
> // is updated it will fire any bindings to it so we
> want to keep
these
> // to a minimum.
> if ( [EMAIL PROTECTED] Attribute] != selectedFlag )
> {
> // The selected flag is different than the
> selectedAttribute
> attribute.
> // Now we make one last check to see if the
> selectedFlag is
false and
> // there is no attribute selectedAttribute. If
> this is the
case, then
> // we do NOT update because having no attribute
selectedAttribute will
> // default to a false. Again, we do this so
> that we update the
xml as
> // infrequently as possible.
> if ( selectedFlag || [EMAIL PROTECTED]
> Attribute] .length()
> 0 )
> {
> [EMAIL PROTECTED] Attribute] =
> String(this. selected) ;
//set the
> checkbox state into the dataProvider
> }
> }
> dispatchEvent( new BaseEvent("selectio nSet",
> selectedFlag) );
> }
>
> // Called by click of the checkbox
> private function onClick(mouseEvent: MouseEvent) : void
> {
> trace("RendererChec kBoxXML:onClick: " + [EMAIL
> PROTECTED]) ;
> // Simply need to trigger the set selected function as
> that is
> where the logic for updating the xml is.
> this.selected = this.selected;
> }
>
> }
> }
>
