RowCommand Event - GridView.FindControls - Check Checkbox Of Linkbutton Clicked Row

I have a gridview in my web page. I have boundcolumn,checkboxcolumn and a linkbutton column. The commandName of the linkbutton column is "Select" The name of the template checkbox is "chkSwapSelect". I want to check the checkbox of the linkbutton clicked row. When i click the linkbutton of the gridview RowCommand Event fires


if e.commandName="Select" then
Dim index as integer=Integer.Parse(e.CommandArgument)
Dim row as GridVIewRow=dgvAllocation.rows(index)
dim chk as checkbox
chk=new checkbox
chk=ctype(row.FindControl("chkSwapSelect"),checkbox) // chk returns nothing
chk.checked=true // object reference not set to an instance of the object
end if

The errors are shown as comments in the above code. finding the controls inside a gridview via RowCommand Event