getting nothing in textbox

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VB

ASP.NET

Dear All,
I have an gridview control where there is a column includes textboxes but
when i submit this gridview data , i am getting nothing while ctype to that textbox.

Below is my code

Dim txtbox As TextBox
        
        Dim SetControlValue As String = ""

txtbox = CType(row.FindControl("gv_NominatedBLDetails__ctl2_txtmbl_no"), TextBox)
                    SetControlValue = txtbox.Text

i am getting nothing for that txtbox.

Please help me out..........