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Troubleshooting PageMethods Is Undefined error - DotNetSpider

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					How to call Server Side function from Client Side Code
using PageMethods in ASP.NET AJAX
Posted by Venkat Reddy Sappidi on March 31, 2008

You cannot call server-side code ‘directly’ from client-side code. That is because by design,
the server side code executes at server side and client side code at the client. However
there are some workarounds. To call serverside code from javascript, you will need to use
AJAX, and the easiest way out, is to use the ASP.NET AJAX Extensions.

One option while using Microsoft ASP.NET AJAX is to call ASP.NET Web services (.asmx files)
from the browser by using client script. The script can call a webservice containing server-
based methods (Web methods) and invoke these methods without a postback and without
refreshing the whole page. However this approach could be overkill sometimes, to perform
the simplest of tasks. Moreover the logic needs to be kept in a separate .asmx file. We need
something that is more ‘integrated’ with our solution.

The option we are going to use in this article involves PageMethods. A PageMethod is
basically a public static method that is exposed in the code-behind of an aspx page and is
callable from the client script. PageMethods are annotated with the [WebMethod] attribute.
The page methods are rendered as inline JavaScript.

Let us explore PageMethods with an example. The example we will be discussing here may
not be the best example to explain PageMethods, but it will give you an idea of how to call
server side code from client side. In this example, we will be connecting to the Customers
table in the Northwind database. We will have some textboxes which will accept the
CustomerID and in turn return the Contact Name of that Customer. The method returning
ContactName will be called whenever the textbox loses focus. We will be using the onblur
event where a javascript code will take in the value(CustomerID) from the textbox. This
javascript function will then call a PageMethod (server side code) which returns the
ContactName without any page refresh.

I assume that you have downloaded and installed ASP.NET AJAX extensions for ASP.NET
2.0. If not, I would advise you to download the extensions from here and install it before
moving ahead. At any point of time, if you find a difficulty in understanding the code,
download the sample project attached with this article at the end.

Step 1: Create an ASP.NET AJAX enabled website. Go to File > New > Website > ASP.NET
AJAX-Enabled Web Site. Give the solution a name and location and click Ok.

Step 2: Drag and drop 2 labels and 4 textbox controls. We will be accepting the
CustomerID from the user in the 2 textboxes and displaying the ‘ContactName’ in the other
two textboxes. The textboxes that will display ‘ContactName’ has some properties set that
will make it appear as a label without a border. Just set the BorderStyle=None,
BorderColor=Transparent and ReadOnly=True. The markup will look similar to the following:

<form id=”form1″ runat=”server”>
        <asp:ScriptManager ID=”ScriptManager1″ runat=”server”/>
        <div>
        <asp:Label ID=”lblCustId1″ runat=”server” Text=”Customer ID
1″></asp:Label>
        <asp:TextBox ID=”txtId1″ runat=”server”></asp:TextBox><br />
            <asp:TextBox ID=”txtContact1″ runat=”server”
BorderColor=”Transparent” BorderStyle=”None”
                ReadOnly=”True”></asp:TextBox><br />
        <br />
        <asp:Label ID=”lblCustId2″ runat=”server” Text=”Customer ID
2″></asp:Label>
        &nbsp;
        <asp:TextBox ID=”txtId2″ runat=”server”></asp:TextBox><br />
            <asp:TextBox ID=”txtContact2″ runat=”server”
BorderColor=”Transparent” BorderStyle=”None”
                ReadOnly=”True”></asp:TextBox>&nbsp;<br />
            </div>
    </form>

Before moving ahead, we will store our connection string information in the Web.config. Add
the following tag below your </configSections> tag. Remember we have created an
‘ASP.NET AJAX enabled website’. The tag </configSections> along with some other tags
automatically get added to the web.config.

<connectionStrings>
            <removename=“all“/>
            <addname=“NorthwindConnectionString“connectionString=“Data
Source=(local); Initial Catalog=Northwind; Integrated Security = SSPI;“/>
      </connectionStrings>

Step 3: Currently we will add a method, ‘GetContactName()’ which will accept a
CustomerID and return the Contact Name information from the Northwind database,
Customer table. We will then transform this method as a PageMethod.

C#

public static string GetContactName(string custid)
    {
         if (custid == null || custid.Length == 0)
             return String.Empty;
         SqlConnection conn = null;
         try
         {
             string connection =
ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].Connectio
nString;
             conn = new SqlConnection(connection);
             string sql = “Select ContactName from Customers where CustomerId
= @CustID”;
             SqlCommand cmd = new SqlCommand(sql, conn);
             cmd.Parameters.AddWithValue(“CustID”, custid);
             conn.Open();
             string contNm = Convert.ToString(cmd.ExecuteScalar());
             return contNm;
         }
         catch (SqlException ex)
         {
             return “error”;
         }
         finally
         {
             conn.Close();
         }
     }

VB.NET

 Public Shared Function GetContactName(ByVal custid As String) As String
        If custid Is Nothing OrElse custid.Length = 0 Then
            Return String.Empty
        End If
        Dim conn As SqlConnection = Nothing
        Try
            Dim connection As String =
ConfigurationManager.ConnectionStrings(“NorthwindConnectionString”).Connectio
nString
            conn = New SqlConnection(connection)
            Dim sql As String = “Select ContactName from Customers where
CustomerId = @CustID”
            Dim cmd As SqlCommand = New SqlCommand(sql, conn)
            cmd.Parameters.AddWithValue(“CustID”, custid)
            conn.Open()
            Dim contNm As String = Convert.ToString(cmd.ExecuteScalar())
            Return contNm
        Catch ex As SqlException
            Return “error”
        Finally
            conn.Close()
        End Try
    End Function

Step 4: We will now transform this method as a PageMethod and then call this method
GetContactName() from client side code; i.e. using JavaScript. To enable the method as a
PageMethod, add the attribute [WebMethod] on top of the method:

C#

[System.Web.Services.WebMethod]
public static string GetContactName(string custid)
{

}

VB.NET

<System.Web.Services.WebMethod()> _
    Public Shared Function GetContactName(ByVal custid As String) As String
   End Function

At the sametime, add the attribute EnablePageMethods=”true” to the ScriptManager as
shown below:

<asp:ScriptManager ID=”ScriptManager1″ runat=”server“
EnablePageMethods=”true”/>
Step 5: Let us now create the JavaScript that will call this server side code. Add a javascript
file called script.js to your solution (Right Click Project > Add New Item > Jscript File >
Rename file to script.js). Add the following code to the javascript file.

function CallMe(src,dest)
 {
      var ctrl = document.getElementById(src);
      // call server side method
      PageMethods.GetContactName(ctrl.value, CallSuccess, CallFailed, dest);
 }
 // set the destination textbox value with the ContactName
 function CallSuccess(res, destCtrl)
 {
     var dest = document.getElementById(destCtrl);
     dest.value = res;
 }
 // alert message on some failure
 function CallFailed(res, destCtrl)
 {
     alert(res.get_message());
 }

Step 6: We now need to reference this JavaScript file from our aspx page and invoke the
‘CallMe()’ method whenever the textbox loses focus. To do so:

Add a reference to the javascript file in the body tag as shown below:

<body>
<script type=”text/javascript” language=”javascript” src=”script.js”>
</script>
    <form id=”form1″ runat=”server”>

………

Step 7: To invoke the methods whenever the textbox looses focus, add these lines of code
in the Page_Load() event

C#

if (!Page.IsPostBack)
        {
            txtId1.Attributes.Add(“onblur”, “javascript:CallMe(‘” +
txtId1.ClientID + “‘, ‘” + txtContact1.ClientID + “‘)”);
            txtId2.Attributes.Add(“onblur”, “javascript:CallMe(‘” +
txtId2.ClientID + “‘, ‘” + txtContact2.ClientID + “‘)”);
        }

VB.NET

If (Not Page.IsPostBack) Then
                  txtId1.Attributes.Add(“onblur”,          “javascript:CallMe(‘” &
txtId1.ClientID & “‘, ‘” & txtContact1.ClientID &          “‘)”)
                  txtId2.Attributes.Add(“onblur”,          “javascript:CallMe(‘” &
txtId2.ClientID & “‘, ‘” & txtContact2.ClientID &          “‘)”)
End If

As shown above, we are using the Attributes.Add that lets us add an attribute to the server
control’s System.Web.UI.AttributeCollection object. The function ‘CallMe’ kept in the
‘script.js’ file will be invoked. We are passing the source and destination textboxes as
parameters. The source textbox will contain the CustomerID. The CustomerID will be looked
up in the Customers table and the corresponding ‘ContactName’ will be retrieved in the
destination textbox.
   Well that is all that is needed to invoke server side code from client side. Run the code.
   Type ‘ALFKI’ in the first textbox and hit the tab key. You will see that the javascript function
   goes ahead and calls the PageMethod GetContactName() using
   PageMethods.GetContactName. It passes the value of the source textbox which contains
   the CustomerID. The ‘ContactName’ returned is displayed in the second textbox below the
   first one, in our case the value displayed is ‘Maria Anders’.

   Troubleshooting: ‘PageMethods Is ‘Undefined’’ error
1. Try setting EnablePageMethods=”true” in the script manager tag

   <asp:ScriptManager ID=”ScriptManager1″ runat=”server”
   EnablePageMethods=”true”/>
2. Don’t add the javascript references or code in the <head /> section. Add it to the <body>
   tag.
   <body>
   <script type=”text/javascript” language=”javascript” src=”script.js”>
   </script>
        <form id=”form1″ runat=”server”>
        </form>

   </body>
3. Page methods needs to be static in code behind.

				
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