Thank you for your answer, but I have the following questions and comments:

Mike Saltzman"]I'm not sure I follow exactly what you are trying to do here.

I have to show the user a list of parent business objects with their list of children business object. In the previous example:unitate is the parent business object, and it has a list of none, one or more gestiune business objects. When the list is refreshed, I don't want to lose the focus on the current selected row, so I'm using the SetCount on the DataSource to set the new number of rows available. After that I am looping each row to set it's data. The UltraGrid updates itself correctly in the case of the root rows with index different than 0, but fails to do so in the case of the root row with index 0.

Mike Saltzman"]The SetCount method is only intended for use when you are loading the data on-demand.

In the Infragistics help page "Load Data On-Demand"(http://help.infragistics.com/Help/NetAdvantage/NET/2008.1/CLR2.0/html/WinDataSource_Load_Data_on_Demand.html) is mentioned: "The CellDataRequested event is fired when a control bound to the WinDataSource requests value for a cell and WinDataSource doesn't have the cell value". In my case the data is already there.

In the documentation page "Use WinDataSource at Run Time" (http://help.infragistics.com/Help/NetAdvantage/NET/2008.1/CLR2.0/html/WinDataSource_Use_WinDataSource_at_Run_Time.html), which is what I am using the following code snippet can be found:

private void Use_WinDataSource_at_Run_Time_Load( object sender, System.EventArgs e)

{

     // structure building code for ultraDataSource -

    // not relevant in this case, I've set it in design time

    // Set the count on the root rows collection to 2.

    this.ultraDataSource1.Rows.SetCount( 2 );

    UltraDataRow row;

    // Initialize rows with data.

    // Get the first row.

    row = this.ultraDataSource1.Rows[0];

    row[ "Col0" ] = "Row 0, Col 0";

    row[ "Col1" ] = "Row 0, Col 1";

    // Initialize the child rows of the row.

    UltraDataRowsCollection childRows = row.GetChildRows( "ChildBand" );

    childRows.SetCount( 2 );

    childRows[0][ "ChildCol0" ] = "Child Row 0, ChildCol 0";

    childRows[0][ "ChildCol1" ] = "Child Row 0, ChildCol 1";

    childRows[1][ "ChildCol0" ] = "Child Row 1, ChildCol 0";

    childRows[1][ "ChildCol1" ] = "Child Row 1, ChildCol 1";

    // Get the second row.

    row = this.ultraDataSource1.Rows[1];

    row[ "Col0" ] = "Row 1, Col 0";

    row[ "Col1" ] = "Row 1, Col 1";

    // Initialize the child rows of the row.

    childRows = row.GetChildRows( "ChildBand" );

    childRows.SetCount( 1 );

}

This was the example I studyed before choosing to implement the solution I've presented in the previous post. The SetCount method is being used on the UltraDataSource to set the number of rows which are afterwards filled with data.

Mike Saltzman"]So if you use SetCount, then you have to handle the other events of the UltraDataSource like CellDataRequested.

I have added a CellDataRequested event listener on the UltraDataSource, and, if I completely fill the root rows and the child rows with data, it is never called.

Mike Saltzman"]If you want to manually populate your data source with data, then you should be adding rows using the Add method.

I hate to do a Clear and the Add on the rows collection, because it looks like unneeded work. All I need is to set the new number of rows and set the data for each one of them.

My question is: why the method I'm using works excellent for all the other root rows with child rows in the shown (the number of child rows is raising or shrinking, the UltraGrid it's updating itself well), except for the first root row (in which although the UltraDataSource has the correct number of rows, the UltraGrid it's not changing the number of the children rows). If I enter a new first root row, it gets all the children rows the last first root row had, and the ex first root row, which is now the second one, is working as it should do. The same way of reseting the rows count and filling the data I am using to work with singleband grids and it works perfectly.