Cross Page Posting in ASP.NET 2.0

Introduction

Almost every web application inputs data from the user and process it, in ASP.NET this process is called page posting. By default in ASP.NET 1.1 page can only post back to itself which some times is not the functionality developers wants. Although it’s possible in ASP.NET 1.1 that one page post backs to other page but this is quite expensive and not the recommended approach. Microsoft realize the importance of cross page posting in gives this functionality in ASP.NET 2.0 along with other features, so in this article I will first discuss the cross page inASP.NET1.1 and then elaborate this concept in ASP.NET 2.0.

Cross Page Postback in ASP.NET 1.1

Asp.net 1.1 developers can achieve the functionality of cross page posting through Server.Transfer Method which preserver the HttpContext of current page before transferring to other page, because HttpContext is preserved you can access the source page’s items collection in target hence called cross page posting.

This functionality comes at price, the basic problem is that this transfer occurs at server level and current page must postback to itself before it can transfer to other page results extra processing overhead.

Security is another problem with the Server.Transfer method along with the viewstate issues; you can find more on MSDN and its knowledge base articles so let’s concentrate on ASP.NET 2.0.

Cross Page postback in ASP.NET 2.0

System.Web.UI.WebControls.IButtonControl interface contains a new property called PostBackUrl which points to the page to which the current page will postback, Button, ImageButton and LinkButton implements this interface and exposes the cross page postback functionality.

When user clicks the button the current page will postback to the specified page which can access the source page controls through Page.PreviousPage property which returns the reference of previous page, once got the reference of previous page you can use the FindControl method to get the reference of particular or you can expose public properties from source page to provide the type safe access i.e

Login.aspx

<asp:Textbox ID="TextBoxUserName" Runat="server" />

<asp:Textbox ID="TextBoxPassword" Runat="server" />

<asp:Button ID="ButtonLogin" Runat="server" Text="Login"

         PostBackUrl="UserAuthenticate.aspx" />

Expose the following properties in code behind file 

public TextBox UserName

{

    get

    {

        return TextBoxUserName;

    }

}

public TextBox Password

{

    get

    {

        return TextBoxPassword;

    }

}

UserAuthenticate.aspx

<%@ PreviousPageType VirtualPath="~/Login.aspx" %>

<script runat="server">   

protected void Page_Load(object sender, System.EventArgs e)

{

    String username = PreviousPage.UserName.Text;

    String password = PreviousPage.Password.Text;

    // Authenticate username/password

}

PreviousPageType directive specifies the virtual path of the source page for strongly typed access to the source page, but the problem with this approach is that you can only specify one previous page type and it cannot be used for pages which can be destination for multiple pages in this case only option left is late bind access using FindControl method or reflection.

It is not necessary that target page always executes as a postback, it can also be execute as stand alone, to determine this Page class contains new property called IsCrossPagePostBack it returns true when page is executing as a result of cross page postback, this behaves exactly same as IsPostBack property. So let’s modify the previous code to incorporate this

if (IsCrossPagePostBack)

{

    String username = PreviousPage.UserName.Text;

    String password = PreviousPage.Password.Text;

    // Authenticate username/password

}