I think you want something like this (forgive the sloppy VB; I'm a C# guy):
--aspx--
<asp:Button ID="MyButton" runat="server" Text="Fill"
OnClick="MyButton_Click" />
<asp:GridView ID="MyGrid" runat="server" ...>
...
</asp:GridView>
--aspx.vb--
Protected Sub MyButton_Click(ByVal sender As Object, ByVal e As EventArgs)
'TODO: Create data source (MyDataSource)
MyGrid.DataSource = MyDataSource
MyGrid.DataBind()
End Sub