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Determine whether uploader has file input (required validation)

By setting required attribute to uploader input element, you can validate the file input has any value in it. In the below sample, set required attribute to the uploader input element and showcase the validation failure message using data-required-message attribute.

tagHelper
required.cs
@{
    var Modalanimation = new Syncfusion.EJ2.Popups.DialogAnimationSettings { Effect = Syncfusion.EJ2.Popups.DialogEffect.Zoom };
    var asyncSettings = new Syncfusion.EJ2.Inputs.UploaderAsyncSettings { SaveUrl = "https://aspnetmvc.syncfusion.com/services/api/uploadbox/Save", RemoveUrl = "https://aspnetmvc.syncfusion.com/services/api/uploadbox/Remove" };
}

<div class="col-lg-8 control-section">
    <div class="control_wrapper">
        <div class="col-lg-12 control-section">
            <h4 class="form-title">Photo Contest</h4>
            <div class="control_wrapper" id="control_wrapper">
                <form id="form1" method="post">
                    <div class="form-group" style="padding-top: 40px; float: left">
                        <div class="e-float-input">
                            <input type="text" id="name" name="name" data-required-message="* Enter your name" required="" data-msg-containerid="nameError">
                            <span class="e-float-line"></span>
                            <label class="e-float-text e-label-top" for="name">Name</label>
                        </div>
                        <div id="nameError"></div>
                    </div>
                    <div id="dropArea">
                        <div id="uploadError" style='float: right;'></div>
                        <div id='customBrowse' class="form-group dropUpload">
                            Drop image here...
                            <ejs-uploader id="UploadFiles" dropArea=".dropUpload" allowedExtensions="image/*" selected="onFileSelect" asyncSettings="@asyncSettings" multiple="true" autoUpload="false"></ejs-uploader>
                        </div>
                    </div>
                    <div class="submitBtn">
                        <button type="button" class="submit-btn e-btn" id="submit-btn">Submit</button>
                        <div class="desc"><span>*This button is not a submit type and the form submit handled from externally.</span></div>
                    </div>
                </form>
                <ejs-dialog id="confirmationDialog" header="Success" showCloseIcon="true" width="335px" visible="false" content="Your details have been updated successfully, Thank you." target="#control_wrapper" isModal="true" animationSettings="@Modalanimation">
                    <e-dialog-buttons>
                        <e-dialog-dialogbutton buttonModel="ViewBag.button" click="closeDialog"></e-dialog-dialogbutton>
                    </e-dialog-buttons>
                </ejs-dialog>
            </div>
        </div>
    </div>
</div>

<script>
    var formID, confirm;
    window.onload = function () {
        inputElement = document.getElementById('upload');
        formID = document.getElementById('form1');
        confirm = document.getElementById("confirmationDialog").ej2_instances[0];
        formObj = new ej.inputs.FormValidator(formID, options);
        document.getElementById('customBrowse').onclick = () => {
            document.getElementsByClassName('e-file-select-wrap')[0].querySelector('button').click();
        };
        document.getElementById('submit-btn').onclick = () => {
            onFormSubmit();
        };
    }
    var options = {
        customPlacement: function (inputElement, errorElement) {
            inputElement = inputElement.closest('.form-group').querySelector('.error');
            inputElement.parentElement.appendChild(errorElement);
        },
        rules: {
            'name': {
                required: true
            }
        }
    };
    function onFileSelect(args) {
        if (args.filesData.length > 0) {
            if (document.getElementsByClassName('upload-image').length > 0) {
                detach(document.getElementsByClassName('imgWrapper')[0]);
            }
            var imageTag = ej.base.createElement('IMG', { className: 'upload-image', attrs: { 'alt': 'Image' } });
            var wrapper = ej.base.createElement('span', { className: 'imgWrapper' });
            wrapper.appendChild(imageTag);
            var rootFile = document.getElementsByClassName('dropUpload')[0];
            rootFile.insertBefore(wrapper, rootFile.firstChild);
            readURL(wrapper, args.filesData[0]);
        }
        args.cancel = true;
    }

    function readURL(li, args) {
        var preview = li.querySelector('.upload-image');
        var file = args.rawFile;
        var reader = new FileReader();
        reader.addEventListener('load', () => { preview.src = reader.result; }, false);
        if (file) { reader.readAsDataURL(file); }
    }
    var options = {};
    formID = document.getElementById('form1');
    var formObj = new ej.inputs.FormValidator(formID, options);
    function onFormSubmit() {
        var formStatus = formObj.validate();
        if (formStatus) {
            formObj.element.reset();
            ej.base.detach(document.getElementsByClassName('imgWrapper')[0]);
            confirm.show();
        }
        document.querySelector('#UploadFiles').setAttribute('data-required-message', '* Choose your image to upload');
        document.querySelector('#UploadFiles').setAttribute('required', '');
        document.querySelector('#UploadFiles').setAttribute('data-msg-containerid', 'uploadError');

    }
    function closeDialog() {
        confirm.hide();
    }

</script>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;

namespace EJ2CoreSampleBrowser.Controllers.TextBoxes
{
    public partial class UploaderController : Controller
    {
        public ActionResult DefaultFunctionalities()
        {
            ViewBag.button = new
            {
                content = "Ok",
                isPrimary = true
            };
            
            return View();
        }
    }
}