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Custom formatting of validation summary and errors

By : franfaccin
Date : October 17 2020, 01:08 AM
should help you out Here are some extension points that you can consider to provide custom rendering for validation summary and field validation errors:
Customize existing validation tag helpers (Register new IHtmlGenerator) Create new validation tag helpers (Register new Tag Helpers) Customize existing validation tag helpers
code :
public void ConfigureServices(IServiceCollection services)
    services.AddTransient<IHtmlGenerator, MyHtmlGenerator>();
using Microsoft.AspNetCore.Antiforgery;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.Routing;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;
using Microsoft.Extensions.Options;
using System.Text.Encodings.Web;

namespace ValidationSampleWebApplication
    public class MyHtmlGenerator : DefaultHtmlGenerator
        public MyHtmlGenerator(IAntiforgery antiforgery, IOptions<MvcViewOptions> optionsAccessor, IModelMetadataProvider metadataProvider, IUrlHelperFactory urlHelperFactory, HtmlEncoder htmlEncoder, ValidationHtmlAttributeProvider validationAttributeProvider) 
            : base(antiforgery, optionsAccessor, metadataProvider, urlHelperFactory, htmlEncoder, validationAttributeProvider)
        public override TagBuilder GenerateValidationMessage(ViewContext viewContext, ModelExplorer modelExplorer, string expression, string message, string tag, object htmlAttributes)
            return base.GenerateValidationMessage(viewContext, modelExplorer, expression, message, tag, htmlAttributes);
        public override TagBuilder GenerateValidationSummary(ViewContext viewContext, bool excludePropertyErrors, string message, string headerTag, object htmlAttributes)
            return base.GenerateValidationSummary(viewContext, excludePropertyErrors, message, headerTag, htmlAttributes);
@using ValidationSampleWebApplication
@using ValidationSampleWebApplication.Models
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@addTagHelper *, ValidationSampleWebApplication
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Mvc.TagHelpers;
using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace ValidationSampleWebApplication
    [HtmlTargetElement("div", Attributes = MyValidationForAttributeName)]
    public class MyValidationTagHelper : TagHelper
        private const string MyValidationForAttributeName = "asp-myvalidation-for";

        public ViewContext ViewContext { get; set; }

        public ModelExpression For { get; set; }
        public override void Process(TagHelperContext context, TagHelperOutput output)
            base.Process(context, output);
            ModelStateEntry entry;
            ViewContext.ViewData.ModelState.TryGetValue(For.Name, out entry);
            if (entry != null && entry.Errors.Count > 0)
                var builder = new TagBuilder("div");
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Mvc.TagHelpers;

namespace ValidationSampleWebApplication
    [HtmlTargetElement("div", Attributes = ValidationForAttributeName)]
    public class MytValidationMessageTagHelper : ValidationMessageTagHelper
        private const string ValidationForAttributeName = "asp-validation-for";
        public MytValidationMessageTagHelper(IHtmlGenerator generator) : base(generator)

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displaying custom message on custom errors in validation summary control on client side?

By : user3211707
Date : March 29 2020, 07:55 AM
Does that help The key is to use the Custom Validation control. This control supports client side scripting (so you can still use your javascript code to do it) but still ties into the validation framework asp.net provides.
From the microsoft article, something like this:
code :
function validateLength(oSrc, args){
   args.IsValid = (args.Value.length >= 8);

<asp:Textbox id="text1" runat="server" text="">

<asp:CustomValidator id="CustomValidator1" runat=server 
      ControlToValidate = "text1"
      ErrorMessage = "You must enter at least 8 characters!"
   ClientValidationFunction="validateLength" >

Return Custom Errors to ajax post error function from JsonResult Method and display it under Validation Summary

By : 陈伟城
Date : March 29 2020, 07:55 AM
seems to work fine From my understanding, when you do an ajax post, it doesn't care if the Model Validation passed or not, it only cares if it got a response from the server. If an Exception gets thrown from the server, then it will hit your ajax error function.
So what I would do is return a json object that lets me know the validation status.
code :
        var modelStateErrors = this.ModelState.Keys.SelectMany(key => this.ModelState[key].Errors);
        var message = "Please fix the following: " + Environment.NewLine;

        foreach (var modelStateError in modelStateErrors)
            message += modelStateError.ErrorMessage + Environment.NewLine;

     return Json(new {success = false, response = message})

 // Do other logic

return Json(new {success = true, response = "Successful message"})
success: function (result) {
            if(result.success === true){
                 $('#status-div').empty().html('<div class="success">' + result.response + '</div>');
            if(result.success === false){
                 $('#status-div').empty().html('<div class="fail">' + result.response + '</div>');


Removing <ul> <li> tag in validation-summary-errors

By : Mali Abhijit
Date : March 29 2020, 07:55 AM
should help you out I have this site that the error message is on this format , Apply list-style property on ul not li. So try something like this
code :
.validation-summary-errors ul { 
        list-style: none;

Knockout Validation: Validation Summary displays required field errors at page load even though no edits were made

By : ashswet
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I found a way to filter for errors corresponding to modified observables.
code :
  self.visibleErrors = ko.computed(function() {
    var errors = [];
    self.errors.forEach(function(observable) {
      if (ko.validation.utils.isValidatable(observable) && !observable.isValid() && observable.isModified()) {
    return errors;

asp-validation-summary shows custom but not model errors

By : Minhazul Hossain
Date : March 29 2020, 07:55 AM
it should still fix some issue Asp-validation-summary in view shows errors added via ModelState.AddModelError, but don't show any model validation errors ("The User field is required."). I'm using Microsoft.AspNetCore.Mvc 1.0.0-rc2-final. Btw: User field is not displayed via the view but correctly identified by EF as a model level error before add. , Change your html:
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