To enable Page methods we need to drag a ScriptManager control to the page and mark  

the EnablePageMethods to “True”.

<asp:ScriptManager ID="ScriptManager1" runat="server"   
      EnablePageMethods="True">
</asp:ScriptManager>

Go the Code behind file of the page and add a static method and mark them as WebMethod. Lets Say the method name is GetPageMethod which returns a status value

[System.Web.Services.WebMethod]        
public static string GetPageMethod()
{
      return "Welcome PageMethods";
}

Now that the method is exposed add a button control and call a client script which accesses the Webmethods of the page

<asp:Button ID="Button1" runat="server" Text="Call Page Methods"  
      OnClientClick="return fun()"/>

In javascript function we can use PageMethods object to call the WebMethod of the page.

function fun()
{     
      PageMethods.GetStatus(onSucceed, onError);
      return false;
}   
function onSucceed(result)
{
      alert(result);        
}
function onError(result)
{      
}

Now run the application and check the result which shows the alert box with value “Active”. The sample application calls the webmethods of the page using client script without full page cycle.

Let’s say if the page method has two input parameters we can pass paramters as given in the below sample:

      PageMethods.GetStatus(“p1”,”p1”,onSucceed, onError);

We can also access the Session , Application and Cache variables data using the Page Methods. For example:

  protected void Page_Load(object sender, EventArgs e)
{      
      HttpContext.Current.Session["key"] = "SomeValue";
      HttpContext.Current.Application["key1"] = "SomeValue1";
}

Accessing the session data in the page methods:

[System.Web.Services.WebMethod]        
public static string GetStatus(string s1, string s2)
{
      return (string)HttpContext.Current.Session["key"];         
} 

We can also return the application and cache data in the similar way.

return (string)HttpContext.Current.Application["key1"];         
return (string)HttpContext.Current.Cache["key"];         

Script Manager and Page Methods

The ScriptManager renders the java script to access the web methods when the EnabledPageMethods is set to “True”.  An JavaScript object Page Methods is created using which we can access the web methods of the page.    

In order to call web methods using PageMethods object we should add a function for Successful Page method call and a function for UnSuccessful Page method call as seen in our sample above. These functions can be treated as Callback functions.

We can also pass parameters to the page method along with references to call backs  separated by “,”.

We can pass n number of parameters to the page methods from the client script which are required for processing and getting the result.

The syntax for calling the page methods using PageMethods object and passing parameters:

      PageMethods.Somemethod(p1,p1,p3,onSucceed,onError); 

Internally the script manager builds the PageUrl and XmlHttpRequest and then post the request to the server to fetch the required result. Ultimately its all the XmlHttpRequest stuff that is wrapped up for easy usage.