GridView Checked Rows Values VB asp.net - asp.net

Question

I have GridView named GridViewTest and the first column in the GridView is a templatefield checkbox named CheckBox1. Im able to loop through all the rows that the GridView contains and display the value in a label named Label2. The issue i'm having is, I only want the rows that are checked to be displayed in the Label2. Can anyone help me?
Protected Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click
Dim str As String = ""
For i As Integer = 0 To GridViewTest.Rows.Count - 1
str = (str + GridViewTest.Rows(i).Cells(0).Text & Convert.ToString(" >> ")) + GridViewTest.Rows(i).Cells(1).Text + " >> " + >GridViewTest.Rows(i).Cells(2).Text + "<br/>"
Next
Label2.Text = str
End Sub
PS: This is VB ASP.NET
<asp:GridView ID="GridViewTest" runat="server"
AutoGenerateColumns="False" BackColor="White" BorderColor="#DEDFDE"
BorderStyle="None" BorderWidth="1px" CellPadding="4"
CssClass="GridviewTable" DataSourceID="SqlDataSourceDetailGrid" EnableTheming="True"
Font-Names="Arial" Font-Size="8pt" ForeColor="Black" GridLines="Vertical"
Height="100%" PageSize="15" TabIndex="25" Width="985px" AllowPaging="True" EnableModelValidation="True">
<FooterStyle BackColor="#CCCC99" />
<HeaderStyle BackColor="#6B696B" CssClass="Freezing" Font-Bold="True"
ForeColor="#FFFFCC" Wrap="False" />
<RowStyle BackColor="#F7F7DE" VerticalAlign="Middle" Wrap="False" />
<AlternatingRowStyle BackColor="White" />
<Columns>
<asp:TemplateField>
<EditItemTemplate>
<asp:CheckBox ID="CheckBox1" runat="server" />
</EditItemTemplate>
<ItemTemplate>
<asp:CheckBox ID="CheckBox1" runat="server" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="TestColumn1" HeaderText="TestColumn1" />
<asp:BoundField DataField="TestColumn2" HeaderText="TestColumn2" />
<asp:BoundField DataField="TestColumn3" HeaderText="TestColumn3" />
<asp:BoundField DataField="TestColumn4" HeaderText="TestColumn4" />
<asp:BoundField DataField="TestColumn5" HeaderText="TestColumn5" />
<asp:BoundField DataField="TestColumn6" HeaderText="TestColumn6" />
</Columns>
<PagerSettings PageButtonCount="20" Position="TopAndBottom" />
<PagerStyle BackColor="#F7F7DE" Font-Size="10pt" ForeColor="Black"
HorizontalAlign="Center" VerticalAlign="Middle" />
<SelectedRowStyle BackColor="#CE5D5A" Font-Bold="True" ForeColor="White" />

Answer 1

If you are using a template field having a checkbox with an id of CheckBox1, then use the code below in the Page_PreRender event.
For Each row As GridViewRow In GridViewTest.Rows
Dim result As Boolean = DirectCast(row.FindControl("CheckBox1"), CheckBox).Checked
if result = True Then
Label2.Text = string.Format("{0},row:{1} is {3}", Label2.Text , row.RowIndex, result);
End If
Next