[flexcoders] sortCompareFunction :: My Solution

[Brendan Meutzner]

Hi All,After coming across the difficulties surrounding the
current sortCompareFunction for the DataGrid, I've come up with a
solution that worked to solve my problem, and I thought might help
others.My particular issue was that I had two columns in my
DataGrid which were dynamically set (that is, the dataField value [a
month] was dynamically set based on a ComboBox setting).  These two
columns would display data allowing a user to compare two months of
data.  A third column used an itemRenderer to display a percentage
value which represented the difference between the first month's column
value, and the second month's column value. (see attached)

Because the information from the 3rd column was being calculated, when
I went to implement sorting for it, I had to look to the
sortCompareFunction.  My solution is as follows:
I created a singleton class to hold my sort functionality, as well
as a few custom properties that I set on headerRelease of the dataGrid.

MyApp.mxml (excerpt)
-----------------------
import helpers.MySingletonSortClass;

<mx:DataGrid headerRelease="setSortValues()">
    <mx:DataGridColumn dataField="{month1Combo.selectedItem.data}" />
    <mx:DataGridColumn dataField="{month2Combo.selectedItem.data}" />
    <mx:DataGridColumn itemRenderer="MyPercentageRendererClass" sortCompareFunction="MySingletonSortClass.sortDifference" />
</mx:DataGrid>

private function setSortValues(event:Event):void
{
    MySingletonSortClass.sortColumn1 = event.target.columns[0].dataField;
    MySingletonSortClass.sortColumn2 = event.target.columsn[1].dataField;
}


MySingletonSortClass.as
-------------------------------
package helpers
{
    public class MySingletonSortClass
    {
        private static var _sortInstance:MySingletonSortClass;

        public static var sortColumn1:String;
        public static var sortColumn2:String;
    
        public function MySingletonSortClass() 
        {    
            if (DataGridSortFunctions._sortInstance != null)
            {
                throw new Error( "Only one please" );    
            }        
        }

        public static function getInstance():MySingletonSortClass
        {
            if (_sortInstance == null)
            {
                _sortInstance = new MySingletonSortClass();
            }    
            return _sortInstance;
        }
        
        //USAGE FUNCTIONALITY
        public static function sortDifference(obj1:Object, obj2:Object):Number
        {
                //I'm now able to access my dataGrid values through obj1[sortColumn1], etc...
                
               //do your sort comparison functionality here and return the usual -1, 0, 1
        }
    }
}


Because the headerRelease event gets fired before the custom sort
happens, I'm able to set the properties inside the singleton class
before the sort functionality takes place.  Solved my problems, and I
hope this idea helps others.


Brendan



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<<attachment: sortCompare1.jpg>>