29 October 2007

The right way of accessing Master page properties from a child page

Master pages are a superbe idea. But sometimes you need to access Master Page properties from the child page. Suppose, for instance, you have a button on the Master Page with a text that you want to be able to set:
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="MyDemoMaster.master.cs" Inherits="MasterPageDemo.MyDemoMaster" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
    <form id="form1" runat="server">
        <asp:button id="btnWithText" runat="server" text="Button">
         <asp:contentplaceholder id="ContentPlaceHolder1" runat="server">
In the Master Page, you can create a property like this:
public string ButtonText
   get { return this.btnWithText.Text;  }
   set { this.btnWithText.Text  = value; }
Unfortunately, if you try to find the property "Master.ButtonText" in the childpage, it won't be available since the "Master" property is of type System.Web.UI.Page, and that does not contain properties of your derived class "MyDemoMaster" This, of course, can be solved by changing the Page_Load of the child page like this:
protected void Page_Load(object sender, EventArgs e)
  MyDemoMaster m = Master as MyDemoMaster;
  m.ButtonText = "My button text";
Congratulations. Your button shows the right text. And you have succeeded into locking your child page to a single master. Your web page will not run when you try to use another master page. Go back to programming class 101 and you don't get any cookies today ;-) The right solution is: create an interface like this:
namespace MasterPageDemo
    public interface IButtonText
        string ButtonText { get;set;}
Open the code behind file of your Master Page and let it implement the interface:
public partial class MyDemoMaster : System.Web.UI.MasterPage, IButtonText
    protected void Page_Load(object sender, EventArgs e)

    public string ButtonText
        get { return this.btnWithText.Text;  }
        set { this.btnWithText.Text  = value; }
And then you make the Page_Load of the child page like this
protected void Page_Load(object sender, EventArgs e)
  IButtonText m = Master as IButtonText ;
  if( m != null ) m.ButtonText = "My button text";
Now the Master Page and Child Page are no longer coupled by name. Any Master Page implementing the IButtonText interface may be used as a Master Page for your child. Checking if it can be casted by testing m != null is a nice encore.

23 October 2007

Calling ASMX web services directly from javascript

The AJAX hype is all around us, and Microsoft provided us with the very neat ASP.NET AJAX extensions and the control toolkit to make things easier. The UpdatePanel and its nephews enjoy a lot of time in the spotlight. The workhorse in the background that makes this all possible can also be used 'raw' - that is, you can call web services directly from javascript utilizing the standard structure of ASP.NET Ajax. It is a very efficient way to transfer data to and from the browser because the server transforms it into JSON - so no large chunks of verbose XML are send through the wire and you don't have to write elaborate pieces of XML-parsing javascript.
Follow the steps below to get things up and running.

This example assumes you have ASP.NET Ajax and de Web Applications already installed.

1. Create a new project of type "ASP.NET AJAX-Enabled Web Application"
This will create a new Web Application with a Default.aspx that already has a script manager on in, and a preconfigured web.config. Call this project WebServiceDemo

2. Add a web service
Right-click on your web application, click Add/New Item and then Web Service. Call this web service "DemoService".

3. Make a web service callable from script
Open code file "Default.aspx.cs". Notice your class "DemoService" sits in a namespace "WebServiceDemo". You will need this knowlegde later.
Add to the top:

using System.Web.Script.Services;
decorate the class with the attribute [ScriptService] and modify the standard hello world method so it looks like this:

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class DemoService : System.Web.Services.WebService
public string HelloWorld( string ToSomeone )
return "Hello World" + ToSomeone;
4. Register the service on the page where you want to call it from
Open Default.aspx in design view and select the ScriptManager1
Select the "Services" property, and click the button that appears
Click "Add", and enter "DemoService.asmx" for the path property
Click OK. The result should look like this:
<asp:ScriptManager ID="ScriptManager1" runat="server" >
    <asp:ServiceReference Path="DemoService.asmx" />
5. Create a client side script to perform the call
Open Default.aspx in source view and enter just before the <head> tag the following code:

<script type="text/javascript">
function CallService()
WebServiceDemo.DemoService.HelloWorld( "Yourself",
Callback );

function Callback( result )
var outDiv = document.getElementById("outputDiv");
outDiv.innerText = result;
6. Create a button to start the web service calling function
Drag a button onto the form
Set the property "OnClientClick" to "CallService();return false;"

7. Create div for the output data
Drag a div (from the HTML tab) onto the form.
Set its id to "outputDiv";

If you did everything correctly, the text "Hello World Yourself" should appear beneath your button, without a visible postback.

Notice the following things:

  • You always need the fully qualified name of the class to call the webservice: WebServiceDemo.DemoService.HelloWorld
  • Calling a webservice from javascript always needs two methods: one to make the actual call, and one to receive the results
  • The callback method is added as an extra parameter to the web service method parameters. In C#, the method has one parameter, so in javascript two.
This sample gives a nice under-the-hood sample of how ASP.NET Ajax transfers data to and from the browser.

Complete code downloadable here.