未将对象引用设置到对象的实例

      If TreeView1.SelectedNode.Text <> "我的通讯录" Then
            Dim string1 As String = TreeView1.SelectedNode.Text
            Dim toshowNode As String = string1.Substring(1, string1.Length - 3)
            Dim toshowView As DataView = New DataView(myDataSet.Tables("lianxiren"))  未将对象引用设置到对象的实例。
            toshowView.RowFilter = "分组 = '" + toshowNode + "'"
            Dim toshowTable As New DataTable("showlianxiren")
            toshowTable = toshowView.ToTable()
            myDataSet.Tables.Add("showlianxiren")

            DataGridView1.AutoGenerateColumns = True
            DataGridView1.DataSource = myDataSet
            DataGridView1.DataMember = "showlianxiren"
     End If