JQuery ajax call to httpget webmethod (c#) not working

I am trying to get an ajax get to a webmethod in code behind. The problem is I keep getting the error "parserror" from the jQuery onfail method.

If I change the GET to a POST everything works fine. Please see my code below.

Ajax Call

<script type="text/javascript">
        var id = "li1234";

        function AjaxGet() {
            $.ajax({
                type: "GET",
                url: "webmethods.aspx/AjaxGet",
                data: "{ 'id' : '" + id + "'}",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                async: false,
                success: function(msg) {
                    alert("success");

                },
                error: function(msg, text) {
                    alert(text);
                }
            });
        }

    </script>

Code Behind

[System.Web.Services.WebMethod]
[System.Web.Script.Services.ScriptMethod(UseHttpGet = true,
    ResponseFormat = System.Web.Script.Services.ResponseFormat.Json)] 
public static string AjaxGet(string id)
{
    return id;
}

Web.config

        <webServices>
            <protocols>
                <add name="HttpGet"/>
            </protocols>
        </webServices>

The URL being used

......../webmethods.aspx/AjaxGet?{%20%27id%27%20:%20%27li1234%27}

As part of the response it is returning the html for the page webmethods.

Any help will be greatly appreciated.

Before all I could say, that you choose not the easiest way. ScriptMethods is easy to use together with ASP.NET ScriptManager and not with jQuery. I’ll recommend you better use JSON-enabled WCF HTTP Services (better as RESTfull Service) instead of ASMX Webservice which you try to use now. Nevertheless, one can makes you code working without using any Microsoft technologies on the client side.

First of all verify Server side.

Rename webmethods.aspx to webmethods.asmx.

Verify that you placed Inside of \ and a httpHandlers for asmx extension (ScriptHandlerFactory) also exist in the config:

<configuration>
  <!-- ... -->
  <system.web>
    <webServices>
      <protocols>
        <add name="HttpGet"/>
      </protocols>
    </webServices>
    <httpHandlers>
      <!-- ... -->
      <add verb="*" path="*.asmx"
           type="System.Web.Script.Services.ScriptHandlerFactory"
           validate="false"/>
    </httpHandlers></system.web></configuration>

Verify that [ScriptService] attribute ([System.Web.Script.Services.ScriptService] if you like full names) set for your class inherited from System.Web.Services.WebService.

Now you could test the service. Open in you Web-Browser URL like http://localhost/webmethods.asmx/AjaxGet?id=li1234 If you receive back something like
<?xml version="1.0" encoding="utf-8" ?>
<string xmlns="http://tempuri.org/">li1234</string>

You can be sure that you service part works fine.

Remark: Independ on “ResponseFormat = System.Web.Script.Services.ResponseFormat.Json” attribute the service answer with XML responses if “Content-Type:application/json;” not set in the request.

Now we’ll fix the client code. I hope that comments which I placed in the following code explain all.

One more small remark. In the last part of code I call one more “complex” web method:

[WebMethod]
[ScriptMethod (UseHttpGet = true, ResponseFormat = ResponseFormat.Json)]
public OutputData AjaxGetMore (InputData input) {
    return new OutputData () {
        id = input.id,
        message = "it's work!",
        myInt = input.myInt+1
    };
}

Where

public class OutputData {
    public string id { get; set; }
    public string message { get; set; }
    public int myInt { get; set; }
}
public class InputData {
    public string id { get; set; }
    public int myInt { get; set; }
}

Now only JavaScript code which use in some places JSON plugin, which could be replaced with Crockford's json2.js, if somebody prefer it.

var id = "li1234";
// version 1 - works
var idAsJson = '"' + id + '"';  // string serializes in JSON format
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGet?id=" + idAsJson,
    contentType: "application/json; charset=utf-8",
    success: function(msg) {
        alert(msg.d);   // var msg = {d: "li1234"} 
    },
    error: function(res, status) {
        if (status ==="error") {
            // errorMessage can be an object with 3 string properties: ExceptionType, Message and StackTrace
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        }
    }
});

// version 2 with respect of JSON plugin
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGet?id=" + $.toJSON(id),
    contentType: "application/json; charset=utf-8",
    success: function(msg) {
        alert(msg.d);   // var msg = {d: "li1234"} 
    },
    error: function(res, status) {
        if (status ==="error") {
            // errorMessage can be an object with 3 string properties: ExceptionType, Message and StackTrace
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        }
    }
});
// version 3 where jQuery will construct URL for us
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGet",
    data: {id: $.toJSON(id)},
    dataType: "json",
    contentType: "application/json; charset=utf-8",
    success: function(msg) {
        alert(msg.d);   // var msg = {d: "li1234"} 
    },
    error: function(res, status) {
        if (status ==="error") {
            // errorMessage can be an object with 3 string properties: ExceptionType, Message and StackTrace
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        }
    }
});
// version 4. We set "Content-Type: application/json" about our data, but we use no 
//            not 'dataType: "json"' parameter. Then we have "Accept: */*" in the request
//            instead of "Accept: application/json, text/javascript, */*" before.
//            Everithing work OK like before.
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGet",
    data: {id: $.toJSON(id)},
    contentType: "application/json; charset=utf-8",
    success: function(msg) {
        alert(msg.d);   // var msg = {d: "li1234"} 
    },
    error: function(res, status) {
        if (status ==="error") {
            // errorMessage can be an object with 3 string properties: ExceptionType, Message and StackTrace
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        }
    }
});
// version 5. If we don't place "Content-Type: application/json" in our reqest we
//            receive back XML (!!!) response with "HTTP/1.1 200 OK" header and 
//            "Content-Type: text/xml; charset=utf-8" which will be placed.
//            How one can read in
// http://weblogs.asp.net/scottgu/archive/2007/04/04/json-hijacking-and-how-asp-net-ajax-1-0-mitigates-these-attacks.aspx),
//             ASP.NET AJAX will not make JSON serialized of response data for
//             security reasons.
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGet",
    data: {id: $.toJSON(id)},
    dataType: "json",
    //contentType: "application/json; charset=utf-8",
    success: function(msg) {
        alert(msg.d);   // var msg = {d: "li1234"} 
    },
    error: function (res, status, ex) {
        // the code here will be works because of error in parsing server response
        if (res.status !== 200) {   // if not OK
            // we receive exception in the next line, be
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        } else {
            alert("status=" + status + "\nex=" + ex + "\nres.status=" + res.status + "\nres.statusText=" + res.statusText +
                    "\nres.responseText=" + res.responseText);
        }
    }
});
// version 6. Send more komplex data to/from the service
var myData = { id: "li1234", myInt: 100}
$.ajax({
    type: "GET",
    url: "/webmethods.asmx/AjaxGetMore",
    data: {input:$.toJSON(myData)},
    dataType: "json",
    contentType: "application/json; charset=utf-8",
    success: function(msg) {
        // var msg = {__type: "Testportal.OutputData", id: "li1234", message: "it's work!", myInt:101}
        alert("message=" + msg.d.message + ", id=" + msg.d.id + ", myInt=" + msg.d.myInt); 
    },
    error: function(res, status) {
        if (status ==="error") {
            // errorMessage can be an object with 3 string properties: ExceptionType, Message and StackTrace
            var errorMessage = $.parseJSON(res.responseText);
            alert(errorMessage.Message);
        }
    }
});

user3927354

I came here looking for the answer... For others, here's the answer.

For security reasons, ASP.Net AJAX page methods only support POST requests.

(From https://stackoverflow.com/a/2397521)

//...
data: { "id" : id },
//...

Data is an object, not a string that looks like an object.

If you use a string, it must be a correctly formatted URL query string, like this:

//...
data: "id=" + encodeURIComponent(id) + "&otherstuff=" + encodeURIComponent(data),
//...

You could also check out http://www.json.org/js.html JSON.stringify where it accepts a json object as the parameter and returns a string.

For those using VB, decorate your method like this:

<WebMethod()>
<ScriptMethod(UseHttpGet:= True, ResponseFormat:= ResponseFormat.Json)>

来源：https://stackoverflow.com/questions/2651091/jquery-ajax-call-to-httpget-webmethod-c-not-working

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