Thanks, that was helpful.  I'm moving in the same direction of setting individual behaviors on the instance of the child grid and might ask couple of questions withing this post framework later.

Hi Maya, you were very helpful and all the sample were to the point, I'll check that latest a bit later, but I want get back for a brief moment to something that took me about the full day to find out :

As I mention somewhere earlier that when I'm adding CellEdit behavior to the child grid  the same way you are in you projects somehow it does not work. Sort funny enough I can break your projects now too, all it needs to switch this two lines :

  e.Row.RowIslands.Add(childGrid);
        //We disable the autogenerated columns and create the columns so that we can have access to them in the columns collection
        childGrid.AutoGenerateColumns = false;

i.e. if childGrid.AutoGenerateColumns = false; executed on existing object first, before adding it to the rowIsland "Celledit" behavior not going to work on the child grid.

This note is to share the solution to the strange problem and also you might know why it happening. It does not look intuitive...

Thanks.

I need to enable postback on the loaded on demand child grid.
There is  RowUpdating event, how I can added to child grid without triggering same event on parent grid.  Further, I actually need it to get triggered rather on cell updating so I can process it on the server side. Can I instead of RowUpdating use cellSelectionChanged and process in on the server  and raise this event ( and process it) only from the child grid ?
Anyway what would be most efficient approach to process change of the value in the child grid cell on the server.
Thanks.

Updating Main Grid.
Maya, I looked at you sample and it does updates the main grid value as expected.
But my scenario is different. I have problem updating main grid right after changes done to child grid in RowUpdating event.  If event triggered by main grid then it is not a problem e.g.      
after line  mr.Amount = 95000;   executed I can see changes on the main grid, if I try to do the same in the child grid section of the same event it’s not working even if I DataBind main grid again. This is the place where   mr.Amount = 35000; got executed.
The issue that I do not know how to address is the following : MainGris get binded on the PageLoad that executed before RowUpdating event, so when value in the master source changed ( mr.Amount = 35000) it could be seen only on the next postback (after any other child grid get expanded).
So somehow if the change occured in main grid and new value assign to underline source (mr.Amount = 95000) then changes can be seen, if event triggered by child grid then changes to main grid ( mr.Amount = 35000) can be seen only after another postback. Can you advise  how to make mr.Amount = 35000 visible without postback.
Project attached
Thanks.

Maya, this dynamic grid does not go easy on me ..
Here the problem :
I modified sample as following in order to have edited values on screen:  
in Page_Load I’ve stored DS into session
// store original dataset in session  
       
       if (!IsPostBack)
       {
…......................................   
           // store original dataset in session  
           Session.Remove("LR2MasterDS");
           Session["LR2MasterDS"] = MasterDS;
           Session.Remove("LR2DetailsDS");

           Session["LR2DetailsDS"] = DetailsDS;
           whdg.DataSource = MasterDS;
           whdg.DataBind();
       }
       else
           whdg.DataSource = (ExhibitLR2MasterDS)Session["LR2MasterDS"];

in the whdg_RowIslandsPopulating  - get the datasource from session :

ExhibitLR2DetalsDS DetailsDS = (ExhibitLR2DetalsDS)Session["LR2DetailsDS"];
ExhibitLR2DetalsDS.type3tblDataTable islandType3Tbl = DetailsDS.type3tbl;
when it gets bind It uses datasource updated in the new added RowUpdating
IslandGrid.DataSource = islandType3Tbl;
IslandGrid.DataBind();

protected void whdg_RowUpdating(object sender, RowUpdatingEventArgs e)
    {

       GridRecord gr = e.Row;
       ContainerGrid g = (ContainerGrid)sender;
       ControlDataField a = g.FindColumn("idLR5Detail");
       if (a != null)
       {
           
           int idMaster = (int) e.Values["idMaster"];
           int idRec    = (int) e.Values["idRec"];
           int newAmnt =  (int) e.Values["Amount"];
           int oldAmnt = (int)e.OldValues["Amount"];
           int nType  = (int) e.Values["Ntype"];
           int dfrnce = (newAmnt - oldAmnt) * ((nType == 1) ? 1 : -1);

           ExhibitLR2DetalsDS DetailsDS = (ExhibitLR2DetalsDS)Session["LR2DetailsDS"];
           ExhibitLR2MasterDS MasterDS = (ExhibitLR2MasterDS)Session["LR2MasterDS"];

            ExhibitLR2DetalsDS.type3tblRow    dr =  DetailsDS.type3tbl.FindByidRec(idRec);
            dr.Amount = newAmnt;
            ExhibitLR2MasterDS.MasterTableRow mr = MasterDS.MasterTable.FindByidMaster(idMaster);
            mr.Amount = mr.Amount + dfrnce;
            Session["LR2DetailsDS"] = DetailsDS;
            Session["LR2MasterDS"] = MasterDS;

            whdg.DataSource = MasterDS;
            whdg.DataBind();
       }
       else
       {
           ExhibitLR2MasterDS MasterDS = (ExhibitLR2MasterDS)Session["LR2MasterDS"];
           int idMaster = (int)e.Values["idMaster"];
           int newAmnt = (int)e.Values["Amount"];
           ExhibitLR2MasterDS.MasterTableRow mr = MasterDS.MasterTable.FindByidMaster(idMaster);
           mr.Amount = newAmnt ;
             Session["LR2MasterDS"] = MasterDS;
           whdg.DataSource = MasterDS;
           whdg.DataBind();
       }

Here is the problem : After row updated it is  posting back and after page_load comes to RowUpdating where Datasources get midfield.  Parent grid get databind and then it goes to
RowIslandsPopulating  where it retrieves the updated DetailsDS from session and does DataBind at the end.  I’m checking in debugger contents of islandGrid.DataSource = islandType3Tbl;  table right before next line ( islandGrid.DataBind(); ) and it is updated table with new values, but in the browser it shows old value. Also the value of the parent grid datasource get modified and it is also reflected in Datasource (MasterDS.MasterDStbl) but old value still shows up.  Is it get cashed somewhere ?  How I can turn it off ?

When the same done to parent grid it goes through the same path, just different branch of RowUpdating and value in browser is new, means it works properly....