I have the following problem:

simple contact form. If I omit for example a required field, then the form displays errors, but the data that was filled does not appear.

I would greatly appreciate if someone can explain to me why the submitted that is not displayed back.

I would expect that CurrentUmbracoPage(); just resubmits the POST method. instead it redirects to the RenderForm. Is this normal? Given that flow, how could I even expect the submitted model given I have a line that creates new one:

            ContactUsViewModel model = this.contactUsViewModelFactory.CreateContactUsViewModel();

I am missing something - either the flow should not be returning to the RenderForm or somehow the old data from the post should be passed to it.

Here is the code:

    [AcceptVerbs(HttpVerbs.Get | HttpVerbs.Post)]
    public ActionResult RenderForm(int id, string recaptchaKey)
    {
        ContactUsViewModel model = this.contactUsViewModelFactory.CreateContactUsViewModel();
        model.Id = id;
        model.RecaptchaKey = recaptchaKey;
        return this.PartialView("~/Views/Partials/Forms/_ContactUsForm.cshtml", model);
    }

    [HttpPost]
    [ValidateInput(false)]
    public async Task<ActionResult> ContactUs(ContactUsViewModel contactUsModel)
    {
        if (!await this.recaptchaService.Validate(this.Request))
        {
            this.ModelState.AddModelError("RecaptchaKey", "Recaptcha error");
        }

        if (this.ModelState.IsValid)
        {
            // send email

            return this.RedirectToUmbracoPage(contactUsModel.Id);
        }

        return this.CurrentUmbracoPage();
    }

The viewmodel is pretty standard I believe:

public class ContactUsViewModel
{
    public int Id { get; set; }

    public string RecaptchaKey { get; set; }

    [Required(ErrorMessageResourceName = "RequiredField", ErrorMessageResourceType = typeof(FormTranslations))]
    public string Name { get; set; }

    [Required(ErrorMessageResourceName = "RequiredField", ErrorMessageResourceType = typeof(FormTranslations))]
    [EmailAddress(ErrorMessageResourceName = "EmailError", ErrorMessageResourceType = typeof(FormTranslations))]
    public string Email { get; set; }

    [Required(ErrorMessageResourceName = "RequiredField", ErrorMessageResourceType = typeof(FormTranslations))]
    public string Message { get; set; }
}

The partial _ContactUsForm.cshtml:

@inherits UmbracoViewPage<ACS.Web.Models.ContactUs.ContactUsViewModel>
@using ACS.Web.Translations;
@{
this.Layout = null;

string currentCulture = (string)ViewBag.CurrentCulture;
string inactiveCulture = (string)ViewBag.InactiveCulture;

}

@using (Html.BeginUmbracoForm("ContactUs", "Contact", new { }, new { id = "contact-us-form" }, FormMethod.Post))

{
<div class="row">
    <div class="col-md-12">
        <div class="ac-contact-us-form-title mx-auto"><h1 @if (currentCulture.Equals("bg-BG")) { <text> style="line-height: 1;" </text> }>@FormTranslations.ContactFormTitle</h1></div>
    </div>
</div>
<div class="row">
    <div class="col-md-8 col-lg-5 mx-auto">
        <div class="ac-contact-us-form-fields">
            <div>@Html.HiddenFor(x => x.Id)</div>

            <div class="ac-contact-us-form-name form-group">
                @Html.TextBoxFor(x => x.Name, new { @class = "form-control", placeholder = FormTranslations.Name })
                @Html.ValidationMessageFor(x => x.Name)
            </div>

            <div class="ac-contact-us-form-emial form-group">
                @Html.TextBoxFor(x => x.Email, new { @class = "form-control", placeholder = FormTranslations.Email })
                @Html.ValidationMessageFor(x => x.Email)
            </div>

            <div class="ac-contact-us-form-message form-group">
                @Html.TextAreaFor(x => x.Message, new { @class = "form-control", @rows = 10, placeholder = FormTranslations.Message })
                @Html.ValidationMessageFor(x => x.Message)
            </div>

            <div class="btn-wrapper" id="contact-submit-btn" type="submit" style="float: right">
                <svg height="50" width="265" xmlns="http://www.w3.org/2000/svg">
                    <rect id="shape1" height="50" width="265" />
                    <rect id="shape" height="50" width="265" />
                    <div id="text">
                        <a href="#">
                            <span class="spot">@FormTranslations.Send</span>
                        </a>
                    </div>
                </svg>
            </div>
            <div class="text-center loader-container hidden">
                <img src="@Url.Content("~/Media/img/loading_spinner.gif")" alt="Alternate Text" />
            </div>
        </div>
    </div>
</div>

<div style="position: relative; z-index: 500;">
    <div>@Html.ValidationMessageFor(x => x.RecaptchaKey)</div>
    <div id='recaptcha' class="g-recaptcha"
         data-sitekey="@Model.RecaptchaKey"
         data-callback="onSubmit"
         data-size="invisible"></div>
</div>
}

And the view itself has just slightly been modified to use the recaptcha:

    <script>
    function onSubmit(token) {
        $(".btn-wrapper").addClass("hidden");
        $(".loader-container").removeClass("hidden");
        $("#contact-us-form").submit();
    }

    function validate(e) {
        e.preventDefault();

        grecaptcha.execute();
    }

    function onload() {
        var element = document.getElementById('contact-submit-btn');
        element.onclick = validate;
    }
</script>
 @{ Html.RenderAction("RenderForm", "Contact", new { id = successPageId, recaptchaKey = RecaptchaSiteKey }); }