Enable or disable ribbon custom action button in SharePoint 2010

Enable or disable ribbon custom action button in SharePoint 2010

http://msdn.microsoft.com/en-us//library/ff458385.aspx
http://msdn.microsoft.com/en-us/library/office/ee537017(v=office.14).aspx

<?xml version="1.0" encoding="utf-8" ?>

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">

  <CustomAction

  Id="AlertRibbonButton"

  RegistrationId="100"

  RegistrationType="List"

  Location="CommandUI.Ribbon"

  Sequence="5"

  Title="Alert Ribbon Button">

    <CommandUIExtension>

      <CommandUIDefinitions>

        <CommandUIDefinition Location="Ribbon.List.Settings.Controls._children">

          <Button

          Id="AlertRibbonButtonId"

          Alt="Alert Ribbon Button"

          Sequence="5"

          Command="AlertRibbonButton"

          Image32by32="/_layouts/images/menulistsettings.gif"

          Image16by16="/_layouts/images/itdcl.gif"

          LabelText="Alert Ribbon Button"

          TemplateAlias="o1" />

        </CommandUIDefinition>

      </CommandUIDefinitions>

      <CommandUIHandlers>

        <CommandUIHandler

        Command="AlertRibbonButton"

        EnabledScript="javascript:        

        function getItemIds()

           {

             var itemIds = '';

             var items = SP.ListOperation.Selection.getSelectedItems();

             var item;

             for(var i in items)

             {

               item = items[i];

               if(itemIds != '')

               {

                 itemIds = itemIds + ',';

               }

               itemIds = itemIds + item.id;

             }     

             alert(itemIds);

           }                        

          var EnableDisable = function() {

          this.clientContext = SP.ClientContext.get_current();

          this.selectedItems = SP.ListOperation.Selection.getSelectedItems(this.clientContext);

          var ci = CountDictionary(selectedItems);       

          return (ci > 0);

          //return (ci == 1); //if we want enable for one item only

        };

        EnableDisable();"

        CommandAction="javascript: alert('Hi Alert!');" />

      </CommandUIHandlers>

    </CommandUIExtension>

  </CustomAction>

</Elements>