How to add Column to Adobe flex mx:DataGrid in mxml and/or actionsctpt?

Question

I have simple mxml code
<mx:DataGrid id="DGG"
             editable="true">
    <mx:dataProvider>
        <mx:Object scheduledDate="4/1/2006"/>
    </mx:dataProvider>
</mx:DataGrid>
<mx:Button id="SetBut"
           label="Set Array as Data Provider"
           click="SetDP(); AddBut.visible = true;"
           x="100.5"
           y="164"
           width="211"/>
<mx:Button id="AddBut"
           label="Add a column!"
           click="AddCol();"
           x="100.5"
           y="194"
           width="211"
           visible="false"/>
<mx:Script>
    <![CDATA[
        import mx.controls.dataGridClasses.DataGridColumn;
        import mx.collections.ArrayCollection;
        [Bindable]
        public var MyAC:ArrayCollection=new ArrayCollection([{scheduledDate: "4/1/2006", homeTeam: "Chester Bucks"}]);
        public function SetDP():void
            DGG.dataProvider=MyAC
        public function AddCol():void
            MyAC.addItem({scheduledDate: "4/5/2007", homeTeam: "Long Valley Hitters", Umpire: "Amanda Hugenkis"});
            DGG.columns.push(new DataGridColumn("Umpire"));
    ]]>
</mx:Script>
I want to add rows to my table datagrid how to do such thing?
How to add Column to Adobe flex mx:DataGrid in mxml and/or actionsctpt?
(You can put this code in Flash or AIR app - it will compile with no errors, but will not add any columns=( )

Answer 1

Change this:
             public function SetDP():void
                DGG.dataProvider=MyAC
                MyAC.addItem({scheduledDate: "4/5/2007", homeTeam: "Long Valley Hitters", Umpire: "Amanda Hugenkis"});
            public function AddCol():void
                var dgc:DataGridColumn = new DataGridColumn("Umpire");
                var ca:Array = DGG.columns;
                ca.push(dgc);
                DGG.columns = ca;
Dany