Image upload with Knockout and webapi c#

Question

I am trying to upload an image using Knokout JS and web api. This my code

<div class="row">
<div class="col-sm-4">
    <h3>Send Feedback</h3>
    <form data-bind="submit: sendFeedback">
        <div class="form-group">
            <label>Feedback</label>
            <textarea class="form-control" data-bind="value: feedbackText"></textarea>
        </div>
        <div class="form-group">
            <label>Version Id</label>
            <input class="form-control" type="text" data-bind="value: versionId" />
        </div>
        <div class="form-group">
            <label>Image</label>

            <input class="form-control" type="file"
                   data-bind="file: {data: fileInput, name: fileName, reader: someReader}" />
        </div>
        <div class="form-group">
            <button type="submit" class="btn btn-default">Submit</button>
        </div>
    </form>
</div>

I am using this custom binding

https://github.com/TooManyBees/knockoutjs-file-binding

Then in my script code I am doing this

    self.sendFeedback = function () {
    self.result('');

    var feedBackData = {
        versionId: self.versionId(),
        text: self.feedbackText(),
        screenShot: self.fileInput
    };

    $.ajax({
        type: 'POST',
        url: apiUrl + '/Feedback/Add',
        contentType: 'application/json; charset=utf-8',
        data: JSON.stringify(feedBackData)
    }).done(function (data) {
        self.result("Done!");
    }).fail(showError);

}

I am uncertain about the server part of the code. I have written this so far

    public void Add(HttpPostedFileBase screenShot, String versionId, String text)
    {
        String imgId = null;

        int count = HttpContext.Current.Request.Files.Count;

        if (screenShot != null && screenShot.ContentLength > 0)
        {
            Images img = Images.Create().Save();
            imgId = img.Id;
            BlobHelper.PutFile(imgId, screenShot.InputStream);
        }

        Feedback.Create(versionId, text, imgId).Save(); 

    }

Any thoughts on how to do this?

Answer 1

The fileInput contains the base64-encoded file data. It's a string, so HttpPostedFileBase would not work.

Change the form HTML:

  <input class="form-control" type="file"
               data-bind="file: {data: fileInput}" />

Change the viewmodel code as follows:

// store file data here
self.fileInput = ko.observable(); // is this present already?

var feedBackData = {
        versionId: self.versionId(),
        text: self.feedbackText(),
        screenShot: self.fileInput()
    };

$.ajax({
        type: 'POST',
        url: apiUrl + '/Feedback/Add',
        contentType: 'application/json; charset=utf-8',
        data: ko.toJSON(feedBackData)
    }).done(function (data) {
        self.result("Done!");
    }).fail(showError);

If the controller method is in an API controller it should accept JSON and the model binder will extract the values:

public void Add(String screenShot, String versionId, String text)
    {
        String imgId = null;

        if(!String.IsNullOrEmpty(screenShot))
        {
            Byte[] data = Convert.FromBase64String(screenShot);

        // rest of code omitted

Sorry have not been able to test this for syntax etc. but should put you on the right track.

A good tip for debugging Knockout pages is to use this line while developing so you can see what is happening in your viewModel:

<pre data-bind="text: ko.toJSON($data, null, 2)"></pre>

See http://www.knockmeout.net/2013/06/knockout-debugging-strategies-plugin.html for more help.