Gridview - Accessing Textbox in outside gridview event when text change event of same gridview textbox in ASP.NET

1. Trigger textbox change Event in inside gridview and make auto post back = true

Setting Current Date

 Protected Sub txtDeliveryDateF_TextChanged(sender As Object, e As System.EventArgs)
        Dim txtDeliveryDateF As TextBox = grdProducts.FooterRow.FindControl("txtDeliveryDateF")
        '   Dim txtDeliveryDateF As TextBox = e.Row.FindControl("txtDeliveryDateF")
        If Len(Trim(txtDeliveryDateF.Text & "")) = 0 Then
            txtDeliveryDateF.Text = Now.Date
        End If

        If Len(Trim(txtDeliveryDateF.Text & "")) <> 0 Then
            Dim dateDeliveryDate As DateTime = Convert.ToDateTime(txtDeliveryDateF.Text)
            Dim txtWeekF As TextBox = grdProducts.FooterRow.FindControl("txtWeekF")
            txtWeekF.Text = GetWeekNumber(dateDeliveryDate)
        End If
    End Sub