Calling Asp.NET web service from javascript (Ajax)-(Passing Parameter-GET)


Hi,

Now we will modify the application that we developed in the previous post to work with parameters

https://nishantrana.wordpress.com/2007/10/18/calling-aspnet-webservice-from-javascript-ajax/

1) First we will modify the default Hello World service to accept a parameter like this

[WebMethod]

public string HelloWorld(string Name)

{

return “Hello “+Name+”!”;

}

2) Add the html textbox control in the webform

<INPUT type=”text” id=”Info”>

3) Add the following in the body

<BODY onload=”getMessage()”>

4) Put the following script in our webpage.

<script language=”javascript”>

var xmlHttp;

function getMessage()

{

xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”);

xmlHttp.open(“get”, “http://localhost/WebService1/Service1.asmx/HelloWorld? name=’Nishant'”, true);

xmlHttp.onreadystatechange=doUpdate;

xmlHttp.send(); return false;

}

function doUpdate()

{

if(xmlHttp.readyState==4)

{

var xmlDoc=xmlHttp.responseXML;

var responseElement=xmlDoc.getElementsByTagName(“string”)[0];

var respText=responseElement.firstChild.nodeValue;

document.forms[0].elements[‘Info’].value=respText;

}

}

</script>

5) We have changed the method of passing the data to server from post to get as we are passing the value for Name by appending it in the url.

6) Right now if we run the application it will give us error as “object not found”.

7) The reason for the error is that we have to make our web service configured for get method.

8- We need to open web.config of our web service and add the following line inside system.web section

<webServices>

<protocols>

<add name=”HttpGet”/>

</protocols>

</webServices>

9) We need to build the service again

10) This time our application should work without any error.

Bye

Calling Asp.NET web service from javascript (Ajax)


Here we will be calling the default helloworld webservice that is already created for us when we open a asp.net webservice project template in Visual Studio.

We’ll just have a textbox(html control) which will display us the Hello World! response returned from the web service.

This is the step we need to follow

1) Create a new ASP.NET WebApplication

2) Put a html textbox control on the form

<input type=”text” id=”info”/>

3) Put this script code in the head section of the aspx page

<script language=”javascript”>

var xmlHttp;

function getMessage()

{

xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”);

xmlHttp.open(“post”, “http://localhost/WebService1/Service1.asmx/HelloWorld&#8221;, false);

xmlHttp.onreadystatechange=doUpdate;

xmlHttp.send();

return false;

}

function doUpdate()

{

if(xmlHttp.readyState==4)

{

var startTag = “<string xmlns=\”http://tempuri.org/\”>”;

var endTag = “</string>”;

var exch;

var valueStart = 0;

var valueEnd = 0;

valueStart = xmlHttp.responseXML.xml.indexOf(startTag, valueEnd) + startTag.length;

valueEnd = xmlHttp.responseXml.xml.indexOf(endTag, valueEnd+1);

exch = xmlHttp.responseXML.xml.substring(valueStart, valueEnd);

document.forms[0].elements[‘Info’].value=exch;

}

</script>

4) Call the getMessage function in the body’s onLoad eventHandler

<BODY onload=”getMessage()”>

5) Run the applicaton. We’ll see the HelloWorld! text in our textbox(‘info’)

Now let us understand what is happening inside the javascript code

xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”)

This line of code creates the XMLHttpRequest object. This object sends request to the server and processes the responses from it.

The above code creates the object specific to Internet Explorer( <=6.o).

It is implemented as Active X for IE. However in IE 7 XMLHttpRequest will come as native JavaScript object.

For other browsers we can write

xmlHttp=new XMLHttpRequest();

or best we can write this

if(window.ActiveXObject)

{

xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”);

}

else if (window.XmlHttpRequest)

{

xmlHttp=new XMLHttpRequest();

}

xmlHttp.open(“post”, “http://localhost/WebService1/Service1.asmx/HelloWorld&#8221;, false);

The open method initializes the connection to the server and informs the xmlHttp object how to connect to the server.

post- it indicates how we want to send the data. It can be “get” as well

url- comes the url where we are connecting

false- this means we are making a synchronous call. To make asychronous call simply set it to true

xmlHttp.onreadystatechange=doUpdate;

This specifies the name of the function to be called whenever the state of the xmlHttpRequest changes

xmlHttp.send();

Send method than makes the request to server. This method would return immediately in case of asynchronous call and it would block until the synchronous response is received from the server.

if(xmlHttp.readyState==4)

It tells about the current state of the request

0- uninitialized

1- loading

2- loaded

3-interactive

4-complete

xmlHttp.responseXML.xml

It returns the current response from server in XML=

<?xml version=”1.0″?>

<string xmlns=”http://tempuri.org/”>Hello World !</string>

Than we are using some javascript functions to get the Hello World! and remove everything else.

document.forms[0].elements[‘Info’].value=exch;

Finally assigning the value to our textBox.

The function doUpdate() can be written differently so that we don’t have to make use of any string functions.

function doUpdate()

{

if(xmlHttp.readyState==4)

{

// Here the server is returning us XML in response so we can make use of responseXML

// Here the browser creates a DOM tree to represent that XML and puts a reference to that DOM tree

// in the request’s (xmlHttp) object’s responseXML

var xmlDoc=xmlHttp.responseXML;

var responseElement=xmlDoc.getElementsByTagName(“string”)[0];

var respText=responseElement.firstChild.nodeValue;

document.forms[0].elements[‘Info’].value=respText;

}

 

However creating a ASP.NET AJAX webservice is little different than our normal ASP.NET web service, and calling them using the ASP.NET AJAX client library is also a bit different

https://nishantrana.wordpress.com/2007/11/06/creating-and-calling-aspnet-ajax-web-service/

Bye

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