flex - Can't find my bug: Group flat data in Advanced Datagrid wont work -

I have an option that is correctly displayed in this advanced datagram:

 < Code> & lt; Mx: Enhanced Data Grid ID = "DrawData DG" Editable = "True" Sorted column = "True" Title Wrap = "true" sortExpertMode = "true" rowCount = "8" y = "10" right = "10" Left = "10" Datasaver = "{} model.drawingsData" & gt; & Lt; Mx: column & gt; & Lt; Mx: AdvancedDataGrid column headline text = "approved in week" datafield = "acceptedinvik" edit = "wrong" view = "true" /> & lt; Mx: AdvancedDataGrid column header text = "DRAWING_PK" dataField = "DRAWING_PK" editable = "incorrect" visible = "false" /> & Lt; Mx: AdvancedDataGrid column header text = "drawing no" datafile = "DRAWING_NO" editable = "wrong" view = "true" /> & Lt; Mx: AdvancedDataGrid column headline text = "Drawing index" datafile = "DRAWING_INDEX" editable = "wrong" view = "true" /> & lt; / Mx: column & gt;  

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According to this explanation I have implemented a grouping collection but it just does not work!

  & lt; Mx: AdvancedDataGrid id = "drawingDataDG" editable = "true" sortableColumn = "true" headerWordWrap = "true" sortExpertMode = "true" rowCount = "8" y = "10" right = "10" left = "10" start Do = "gc.refresh ();" & Gt; & Lt; Mx: dataProvider & gt; & Lt; Mx: GroupingClean ID = "GC" Source = "{Model. Drawings Data}" & gt; & Lt; Mx: grouping & gt; & Lt; Mx: Grouping Field Name = "Approved Invoke" / & gt; & Lt; / Mx: Grouping & gt; & Lt; / Mx: GroupingCollection & gt; & Lt; / Mx: dataProvider & gt; & Lt; Mx: column & gt; & Lt; Mx: AdvancedDataGrid column headline text = "approved in week" datafield = "acceptedinvik" edit = "wrong" view = "true" /> & lt; Mx: AdvancedDataGrid column header text = "DRAWING_PK" dataField = "DRAWING_PK" editable = "incorrect" visible = "false" /> & Lt; Mx: AdvancedDataGrid column header text = "drawing no" datafile = "DRAWING_NO" editable = "wrong" view = "true" /> & Lt; Mx: AdvancedDataGrid column headline text = "Drawing index" datafile = "DRAWING_INDEX" editable = "wrong" view = "true" /> & lt; / Mx: column & gt; & Lt; / Mx: AdvancedDataGrid & gt;  

Please tell me which extra information do you need?