Récupérer le résultat d'un SELECT (VB.net)

cnx.open()
com=new sqlcommand("select...",cnx)
TextBox1.Text = com.ExecuteScalar()
cnx.close()

Public Class Form1
Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
ChargerDonnees()
End Sub

Private Sub ChargerDonnees()
        Dim connectString As String = "Server=ALI\SQLEXPRESS;Database=TWO;Trusted_Connection=True;"
        Dim connection As New System.Data.SqlClient.SqlConnection(connectString)
        Dim command As New System.Data.SqlClient.SqlCommand("SELECT * FROM assia where testoo='" & TextBox1.Text & "'", connection)
        Dim dt As New DataTable
        Dim adpt As New Data.SqlClient.SqlDataAdapter(command)
        Try
            connection.Open()
            adpt.Fill(dt)
            DataGridView1.DataSource = dt
        Finally
            connection.Close()
        End Try
End Sub
End Class

Me.TextBox1.Text = Form1.TextBox1.Text

Public Class Form1
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim connectString As String = "Server=ALI-582A65A96CB\SQLEXPRESS;Database=ONE;Trusted_Connection=True;"
        Dim connection As New System.Data.SqlClient.SqlConnection(connectString)
        connection.Open()
        Dim command As New System.Data.SqlClient.SqlCommand("SELECT * FROM assia ", connection)
        Dim mook As DataTable
        Dim hana As New Data.SqlClient.SqlDataAdapter(command)
        Dim DataGridView1 As New DataGridView

        hana.Fill(mook)  //  ici il bloque lors du debogage il me dit : la valeur ne peut pas etre null 

        DataGridView1.ColumnHeadersVisible = True  // ici il n'y a plus autogeneratecolumns
        DataGridView1.DataSource = mook
        DataGridView1.Refresh()
        connection.Close()


    End Sub

  Dim command As New System.Data.SqlClient.SqlCommand("SELECT * FROM assia where testoo='" & textBox1.SelectedItem & "' ", connection)