yavsc/src/Yavsc.Org/Views/Shared/_DropFiles.cshtml

@section header{
<style>
 .box__dragndrop,
.box__uploading,
.box__success,
.box__error {
  display: none;
}
.box.has-advanced-upload {
  background-color: white;
  outline: 2px dashed black;
  outline-offset: -10px;
}
.box.has-advanced-upload .box__dragndrop {
  display: inline;
}
.box.is-dragover {
  background-color: grey;
}
</style>
  <link rel="stylesheet" href="~/css/main/dropzone.min.css" asp-append-version="true"/>
  <link rel="stylesheet" href="~/css/main/dropzone-basic.min.css" asp-append-version="true"/>
  <script src="~/js/dropzone.bundle.min.js" asp-append-version="true"></script>
}

@section scripts{
<script>
$(document).ready(function(){

  var isAdvancedUpload = function() {
  var div = document.createElement('div');
  return (('draggable' in div) || ('ondragstart' in div && 'ondrop' in div)) && 'FormData' in window && 'FileReader' in window;
}();

  var $form = $('.box');

if (isAdvancedUpload) {
  $form.addClass('has-advanced-upload');
}
if (isAdvancedUpload) {

  var droppedFiles = "false";

  $form.on('drag dragstart dragend dragover dragenter dragleave drop', function(e) {
    e.preventDefault();
    e.stopPropagation();
  })
  .on('dragover dragenter', function() {
    $form.addClass('is-dragover');
  })
  .on('dragleave dragend drop', function() {
    $form.removeClass('is-dragover');
  })
  .on('drop', function(e) {
    droppedFiles = e.originalEvent.dataTransfer.files;
  });

}
$form.on('submit', function(e) {
  if ($form.hasClass('is-uploading')) return false;

  $form.addClass('is-uploading').removeClass('is-error');

  if (isAdvancedUpload) {
    // ajax for modern browsers
  } else {
    // ajax for legacy browsers
  }
});
});

</script>
}

<form class="box" method="post" action="~/UserFiles/Create" enctype="multipart/form-data">
  <div class="box__input">
    <input class="box__file" type="file" name="files[]" id="file" data-multiple-caption="{count} files selected" multiple />
    <label for="file"><strong>Choose a file</strong><span class="box__dragndrop"> or drag it here</span>.</label>
    <button class="box__button" type="submit">Upload</button>
  </div>
  <div class="box__uploading">Uploading&hellip;</div>
  <div class="box__success">Done!</div>
  <div class="box__error">Error! <span></span>.</div>
</form>