How to maintain datagridview checkbox column checkstate when filtering

I have a dgvw.It loads data from an sql database.Now, i added a checkbox column to the dgvw.My winform also has a textbox that is used to search in/filter the datagridview. Here is my code:

Code:

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Private Sub Contact_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        filterdata("")
    Private Sub filterdata(valuetosearch As String)
        con.Open()
        Dim cmd As New SqlCommand("Select * from Contacts where CONCAT([Unique id],Prefix,[First name],[Last name],Gender,Title,Company,Phone,Mobile,Fax,[b.email],[p.email],Reference,Address,[Address 2],Country,City,Zip,Facebook,GooglePlus,Instagram,Twitter,Website,Salary,Currency,[Group],[Id/Status],Note,[Added by]) like '%" & valuetosearch & "%' ", con)
        Dim reader As SqlDataReader = cmd.ExecuteReader
        Dim dt As New DataTable
        dt.Load(reader)
        userdatagrid.AutoGenerateColumns = True
        userdatagrid.DataSource = dt
        userdatagrid.Refresh()
        con.Close()
    End Sub
    Private Sub searcgcon_TextChanged(sender As Object, e As EventArgs) Handles searcgcon.TextChanged
        If searcgcon.Text = "" Then
            filterdata("")
            entrylabel.Text = "There are/is " & userdatagrid.Rows.Count & " contact entries"
        Else
            filterdata(searcgcon.Text)
            entrylabel.Text = "There are/is " & userdatagrid.Rows.Count & " contact entries that contain your query :" & searcgcon.Text
        End If
    End Sub

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The problem with this code is, suppose i have checked a row's checkbox then i try to type something in the textbox/filter using the textbox.But as soon as i start typing the checkbox that was checked earlier becomes unchecked.I know i am wrong some where.I got this code from youtube and stackoverflow.So please help me..How do i maintain the checkstate while filtering ?