Cross-Page Posting in ASP.NET Web Pages

ASP.NET by default, submits the form to the same page. Cross page posting is submitting the form to a different page. This is usually required when you are creating a multi page form to collect information from the user on each page. When moving from the source to the target page, the values of controls in the source page can be accessed in the target page.

To use cross-page posting, you have to use the PostBackURL attribute to specify the page you want to post to.

Follow these steps :

Step 1: Create a new ASP.NET website called CrossPagePosting. By default, the website is created with a single webpage, Default.aspx. Right click the project in the Solution Explorer > Add New Item >Web Form. Keep the original name Default2.aspx and click ‘Add’. The website will now contain two pages, Default.aspx and Default2.aspx.

Step 2: On the source page, Default.aspx, drop a button on the form. Set the text of the button as ‘TargetButton’. Set the ‘PostBackUrl’ property of a Button to the URL of the target page, Default2.aspx.

<asp:Button ID="Button1" runat="server" PostBackUrl="~/Default2.aspx" Text="TargetButton" /></div>

Step 3: In the target page Default2.aspx, drop a label on the page from the toolbox.

Step 4: In the Page_Load() of Default2.aspx, you can then access the ‘PreviousPage’ property to check if the page is being accessed as Cross Page postback.

protected void Page_Load(object sender, EventArgs e)

{

       if (Page.PreviousPage != null)

       {

 }

}

Step 5: To retrieve values from the source page, you must access controls using the ‘FindControl()’ method of the ‘PreviousPage’. We will be accessing the Text property of the Button control placed in Default.aspx.

protected void Page_Load(object sender, EventArgs e)

{

        if (Page.PreviousPage != null)

        {

            Button btn = (Button)(Page.PreviousPage.FindControl("button1"));

            Label1.Text = btn.Text;

        }

}

Step 6: In the Solution Explorer, right click Default.aspx > ‘Set as Start Page’. Run the application and click on the button. As you can observe, the page is posted to Default2.aspx and the value containing the name of the button control gets displayed in the label.

Difference between Server.Transfer and Cross Page Posting

One could argue that even the ‘Server.Transfer’ method can be used to move between pages. However there are a few differences between ‘Server.Transfer’ and ‘Cross Page’ Posting.

In ‘Server.Transfer’, the URL doesn't change whereas in cross page posting, the form is submitted to a different page, thereby changing the url.

The Server.Transfer method is a server-based operation whereas cross-page postback is a client-based transfer.

Note: To determine whether the page was invoked from a cross-page posting or a Server.Transfer operation, the Page class exposes a property named IsCrossPagePostBack.