Null parameters doing HTTP POST from Ajax to Web API

Question

I've read several StackOverflow posts about this and corrected my code several times but I cant get my webAPI post method to work. I'm trying to receive a post parameter but it comes always null.

What I am trying to do is receiving a base64 string that represents a canvas that is creating with jquery when the user clicks the button:

function MakePhoto(ctrl) {

    html2canvas(ctrl, {
        onrendered: function (canvas) {

            var canvasData = canvas.toDataURL()
            jQuery.ajax({
                url: "../api/webinfo",
                type: "POST",
                data: { imagedata: canvasData },
                success: function () {
                    alert("success");

                },
                error: function () {
                    alert("failure");
                }
            });

        }
    });

}

my WebInfoController.cs looks like this:

 public void Post([FromBody]string imagedata)
 { 
            
 }

imagedata parameter comes always NULL

And this are the headers I am receiving at webapi:

"Method: POST,

RequestUri: 'http://myhost/RestFulApi/api/webinfo'

Content: System.Net.Http.StreamContent

User-Agent: Chrome/27.0.1453.94

Content-Length: 42226

Content-Type: application/x-www-form-urlencoded; charset=UTF-8}

I hope you could help me.

Thanks

And what does canvas.toDataURL() return, are you sure it's not null? insert a console.log(canvasData) before your ajax-request, what's logged in the browser console? — anderssonola
– anderssonola, Commented Jun 4, 2013 at 15:14
I think you may need to add dataType: "json" to your ajax call. — jeffesp
– jeffesp, Commented Jun 4, 2013 at 15:17
I added dataType: "json" and It is still not working :(. @soderslatt yeah, I am debugging with chrome and it is not null. I can see the base64 string — Carlos Landeras
– Carlos Landeras, Commented Jun 4, 2013 at 19:31

Carlos Landeras · Accepted Answer · 2013-06-05 13:18:19Z

3

OK, I found the problem after some hours researching. I had to pass the data parameter to ajax function using:

"=" + canvasdata, without the parameter name:

jQuery.ajax({
                url: "../api/webinfo",
                type: "POST",
                data: "=" + canvasData,
                success: function (response) {
                    alert(response);

                },
                error: function (response) {
                    alert(response.responseText);
                }
            });

answered Jun 5, 2013 at 13:18

Carlos Landeras

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