Cross page posting in asp.net - Part 55

Suggested Videos
Part 52 - Response.Redirect in asp.net
Part 53 - Server.Transfer in asp.net
Part 54 - Server.execute in asp.net

The following are the different page navigation techniques in asp.net
1. Hyperlink control - Discussed in Part 13 and Part 51 of the ASP.NET video series
2. Response.Redirect - Discussed in Part 52
3. Server.Transfer - Discussed in Part 53
4. Server.Execute - Discussed in Part 54
5. Cross-Page postback
6. Window.Open 



In this video we will discuss about Cross page posting. Cross page posting allows to post one page to another page. By default, when you click a button, the webform posts to itself. If you want to post to another webform on a button click, set the PostBackUrl of the button, to the page that you want to post to.



WebForm1.aspx code: Notice that, the PostBackUrl property of the button with ID=btnCrossPagePostback is set to WebForm2.aspx. When this button is clicked WebForm1.aspx gets posted to WebForm2.aspx.
<div style="font-family: Arial">
    <table>
        <tr>
            <td colspan="2">
                <h1>
                    This is WebForm1</h1>
            </td>
        </tr>
        <tr>
            <td>
                <b>Name</b>
            </td>
            <td>
                :<asp:TextBox ID="txtName" runat="server">
                </asp:TextBox>
            </td>
        </tr>
        <tr>
            <td>
                <b>Email</b>
            </td>
            <td>
                :<asp:TextBox ID="txtEmail" runat="server">
                </asp:TextBox>
            </td>
        </tr>
        <tr>
            <td colspan="2">
                <asp:Button ID="btnCrossPagePostback" runat="server" 
                Text="Cross Page Postback - WebForm2" 
                Width="250px" PostBackUrl="~/WebForm2.aspx"/>
            </td>
        </tr>
        <tr>
            <td colspan="2">
                <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
                    Text="Server.Transfer - WebForm2" Width="250px" />
            </td>
        </tr>
        </table>
</div>

WebForm1.aspx.cs code:
protected void Button1_Click(object sender, EventArgs e)
{
    Server.Transfer("~/WebForm2.aspx");
}

WebForm2.aspx code:
<div style="font-family: Arial">
    <table>
        <tr>
            <td colspan="2">
                <h1>This is WebForm2</h1>
            </td>
        </tr>
        <tr>
            <td>
                <b>Name</b>
            </td>
            <td>
                :<asp:Label ID="lblName" runat="server">
                </asp:Label>
            </td>
        </tr>
        <tr>
            <td>
                <b>Email</b>
            </td>
            <td>
                :<asp:Label ID="lblEmail" runat="server">
                </asp:Label>
            </td>
        </tr>
        <tr>
            <td colspan="2">
                <asp:Label ID="lblStatus" runat="server"
                ForeColor="Red" Font-Bold="true"></asp:Label>
            </td>
        </tr>
        </table>
</div>

WebForm2.aspx.cs code: Page.IsCrossPagePostBack Property is used to indicate whether the page is involved in a cross-page postback.
protected void Page_Load(object sender, EventArgs e)
{
    Page previousPage = Page.PreviousPage;
    if (previousPage != null && previousPage.IsCrossPagePostBack)
    {
        lblName.Text = ((TextBox)previousPage.FindControl("txtName")).Text;
        lblEmail.Text = ((TextBox)previousPage.FindControl("txtEmail")).Text;
    }
    else
    {
        lblStatus.Text = "Landed on this page using a technique other than cross page post back";
    }
}

The problem with FindControl() method is that, if you mis-spell the ControlID, we could get a runtime NullRefernceException. In the next video we will discuss about obtaining a strongly typed reference to the previous page, which can avoid NullRefernceExceptions.