Use of viewstate in rowdatabound

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ASP.NET

Hello friends,
I trying to use viewstate in RowDataBound event of grid.

ViewState.Add("ddlGClient", ddlGClient)
ViewState.Add("ddlGBrandCategory", ddlGBrandCategory)

Problem is, when I click on edit link the grid does not go to edit mode.
But when I remove the code, the grid goes to edit mode (Controls in EditItemTemplete gets visible)

Basically what I'm trying cascading dropdown in grid. I'm saving this control in viewstate and then I'm pass it to following event

Protected Sub ddlGClient_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)      fillBrandCategorydropdown(CType(ViewState(ddlGClient),DropDownList).SelectedValue)
End Sub

What is the logic behind grid not getting into edit mode?<br />
Why the RowDataBound event is called twice for each row?

Any idea?

Thanks in advance