Here is a small example that will clear up the things further:
This is the code for my previousPage:
<asp:TextBox ID="txtName" runat="server" />
<asp:Button ID="Button1" runat="server" PostBackUrl="~/FirstPage.aspx" Text="Button" OnClick="Button1_Click" />
And here is the page that access the PreviousPage.
protected void Page_Load(object sender, EventArgs e)
{
if (PreviousPage != null)
{
TextBox tb = PreviousPage.FindControl("txtName") as TextBox;
Response.Write(tb.Text);
}
if (!Page.IsPostBack)
{
}
}
If you are not able to find the control in the PreviousPage then you can use properties in the Previous to access the value of the control. Like the following:
public class MyPreviousPage : ....
public string Name { return txtName.Text; }
Now, in the main page you can access like this:
MyPreviousPage.Name
You will also need to add the following directive in the main page (NOT Previous Page)
<%@ PreviousPageType VirtualPath="~/MyPreviousPage.aspx" %>