Parameter Data Null Ajax to MVC Controller

Question

Originally, I was passing one parameter to my MVC Controller via Ajax and it was working correctly. The parameter data was being received without any problems. However, I now need to pass an extra parameter and when I do this, neither parameter is sending data to the Controller? Thanks!

Ajax Code:

        function uploadFile() {
        var fileData = new FormData($(form1)[0]); //THIS IS A FILE UPLOAD
        var details = JSON.stringify(markers); //MARKERS IS AN ARRAY

        $.ajax({
            url: '../Home/FilePost',
            type: 'Post',
            success: function (result) {
                var newWindow = window.open('LasView?fileName=' + result, "", "new window");

            },
            error: function (xhr, status, error) {
                alert(xhr.responseText);
            },
            xhr: function () {  // Custom XMLHttpRequest
                var myXhr = $.ajaxSettings.xhr();
                if (myXhr.upload) { // Check if upload property exists
                    // TODO...
                }
                return myXhr;
            },
            error: function () { },
            data: { filePost: fileData, googleMarkers: details },
            cache: false,
            contentType: false,
            processData: false
        });
    }

My Controller:

[HttpPost]
public string LasPost(HttpPostedFileBase filePost, string googleMarkers){
return something;
}

My Array:

 var markerObject = {
     lat: marker.position.lat(),
     lng: marker.position.lng()
    };
     markers.push(markerObject);

You cannnot mix FormData and objects - you need to append the extra data to FormData — user3559349
– user3559349, Commented Apr 11, 2018 at 11:06
But it makes no sense to make the googleMarkers a string if its an array - what it the array? — user3559349
– user3559349, Commented Apr 11, 2018 at 11:07
It's an array of objects, so I just stringify it. What's wrong that? Is that a problem? — JohnTheWizard
– JohnTheWizard, Commented Apr 11, 2018 at 11:09
Why in the world would you convert it to a string and then have to convert it back again in the controller? Show what it is (just 1 or 2 items) so that an answer can be added) — user3559349
– user3559349, Commented Apr 11, 2018 at 11:11

user3559349 · Accepted Answer · 2018-04-11 11:42:23Z

You cannot mix FormData and objects. You must .append() each name/value pair to the FormData instance.

Because you stringified your array, and are binding to a string googleMarkers parameter, then your code would need to be

function uploadFile() {
    var fileData = new FormData($(form1)[0]); //THIS IS A FILE UPLOAD
    var details = JSON.stringify(markers); //MARKERS IS AN ARRAY

    fileData.append('googleMarkers', details); // append the name/value pair
    $.ajax({
        ....
        data: fileData, // send only the FormData instance
        ....
    });
})

However you should be taking advantage of MVC's model binding features and posting data which binds to a model representing your coordinates, for example

public class Coordinate
{
    public double Latitude { get; set; }
    public double Longitude { get; set; }
}

and the POST method would then be

[HttpPost]
public string LasPost(HttpPostedFileBase filePost, IEnumerable<Coordinate> googleMarkers)

and to send that data

var fileData = new FormData($(form1)[0]);
for(var i = 0; i < markers.length; i++)
{
    fileData.append('[' + i + '].Latitude', markers[i].lat);
    fileData.append('[' + i + '].Longitude', markers[i].lng);   
}
$.ajax({
    ....
    data: fileData,
    ....
});

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