<!--标签助手版form-->
<form asp-controller="Home" asp-action="Index" class="form-horizontal" method="post">

</form>
<!--Html帮助类版form-->
@using (Html.BeginForm("Index", "Home", FormMethod.Post,, new { Class = "form-horizontal" }))
{

}

public class SignUpViewModel
 {
 [Required]
 [Display(Name ="用户名")]
 [MaxLength(30,ErrorMessage = "用户名不能超过30")]
 public string UserName { get; set; }

 [Required]
 [DataType(DataType.Password)]
 [RegularExpression(@"((?=.*\d)(?=.*\D)|(?=.*[a-zA-Z])(?=.*[^a-zA-Z]))^$",ErrorMessage ="密码至少包含两种以上字符")]
 [Display(Name ="密码")]
 public string Password { get; set; }

 [DataType(DataType.MultilineText)]
 public string Description { get; set; }
 }

<form asp-controller="Home" asp-action="SignUp" method="post" class="form-horizontal">
 <div class="form-group">
 <label asp-for="UserName"></label>
 <input asp-for="UserName" />
 <span asp-validation-for="UserName"></span>
 </div>
 <div class="form-group">
 @Html.LabelFor(m=>m.Password)
 @Html.PasswordFor(m=>m.Password)
 @Html.ValidationMessageFor(m=>m.Password)
 </div>
 <div class="form-group">
 <label asp-for="Description"></label>
 <textarea asp-for="Description"></textarea>
 <span asp-validation-for="Description"></span>
 </div>
 <div class="form-group">
 <input type="submit" value="提交" />
 <input type="reset" value="重置" />
 </div>
</form>

public IActionResult SignUp(SignUpViewModel model)
 {
  if (ModelState.IsValid)
  {
  return RedirectToAction("Index");
  }
  else
  {
  return RedirectToAction("Index",model);
  }
 }

protected IHtmlGenerator Generator { get; }

 [HtmlAttributeNotBound]
 [ViewContext]
 public ViewContext ViewContext { get; set; }

 /// <summary>
 /// An expression to be evaluated against the current model.
 /// </summary>
 [HtmlAttributeName(ForAttributeName)]
public ModelExpression For { get; set; }

//自定义标签助手名为bg-form
 [HtmlTargetElement("bg-form")]
 public class FormTagHelper : TagHelper
 {
  [ViewContext]
  [HtmlAttributeNotBound]
  public ViewContext ViewContext { get; set; }

  [HtmlAttributeName("asp-for")]
  public ModelExpression For { get; set; }

  protected IHtmlGenerator Generator { get; }

  public FormTagHelper(IHtmlGenerator generator)
  {
   Generator = generator;
  }

  [HtmlAttributeName("asp-controller")]
  public string Controller { get; set; }

  [HtmlAttributeName("asp-action")]
  public string Action { get; set; }

  //异步方法
  public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
  {
   output.TagName = "form";
   if (!string.IsNullOrWhiteSpace(Controller))
   {
    output.Attributes.Add("action", "/" + Controller + "/" + Action);
   }

   output.Attributes.Add("class", "form-horizontal");

   //获取子属性
   var props = For.ModelExplorer.Properties;
   foreach (var prop in props)
   {
    //生成表单
    var div = new TagBuilder("div");
    div.AddCssClass("form-group");
    var label = Generator.GenerateLabel(ViewContext, prop, null, prop.Metadata.DisplayName, null);
    var input = Generator.GenerateTextBox(ViewContext, prop, prop.Metadata.PropertyName, null, null, null);
    var span = Generator.GenerateValidationMessage(ViewContext, prop, prop.Metadata.PropertyName, null, ViewContext.ValidationMessageElement, null);
    div.InnerHtml.AppendHtml(label);
    div.InnerHtml.AppendHtml(input);
    div.InnerHtml.AppendHtml(span);
    output.Content.AppendHtml(div);
   }
   //添加按钮
   var btn = new TagBuilder("div");
   btn.AddCssClass("form-group");
   var submit = new TagBuilder("input");
   submit.Attributes.Add("type", "submit");
   submit.Attributes.Add("value", "提交");
   var reset = new TagBuilder("input");
   reset.Attributes.Add("type", "reset");
   reset.Attributes.Add("value", "重置");
   btn.InnerHtml.AppendHtml(submit);
   btn.InnerHtml.AppendHtml(reset);
   output.Content.AppendHtml(btn);
   //将原有的内容添加到标签内部
   output.Content.AppendHtml(await output.GetChildContentAsync());

  }
 }

<bg-form asp-controller="Home" asp-action="SignUp" asp-for="@Model">
</bg-form>