Razor Pages Custom Tag Helper 2 Way Bind - asp.net-core

Question

I am wanting to create a custom tag helper in razor pages which binds to a custom model but the value is not being read back into the modal on post, below is my TagHelper code
[HtmlTargetElement("kenai-date", TagStructure = TagStructure.WithoutEndTag)]
public class Date : TagHelper
{
//public string Value { get; set; }
public ModelExpression AspFor { get; set; }
public override void Process(TagHelperContext context, TagHelperOutput output)
{
output.TagName = "input";
output.TagMode = TagMode.SelfClosing;
output.Attributes.Add("value", this.AspFor.Model);
}
}
I am using the TagHelper with the below code
<kenai-date asp-for="DateValue" />
'DateValue' is a public property on the page, when first rendering the page the value of DateValue is correctly visible in the TagHelper Input element, if I force an OnPost, the value is removed.
I have applied the same to a standard input element with asp-for set and that works fine so suspect I am missing something in my TagHelper.

Answer 1

Asp.net core bind model data with name attribute.You use a custom tag helper,so it will get html like <input value="xxx">.So when form post,you cannot bind model data with name attribute,and when return Page in OnPost handler,model data is null.You need to add name attribute to <kenai-date asp-for="DateValue" />.Here is a demo:
TestCustomTagHelper.cshtml:
<form method="post">
<kenai-date asp-for="DateValue" name="DateValue" />
<input type="submit" />
</form>
TestCustomTagHelper.cshtml.cs:
public class TestCustomTagHelperModel : PageModel
{
[BindProperty]
public string DateValue { get; set; }
public void OnGet()
{
DateValue = "sss";
}
public IActionResult OnPost()
{
return Page();
}
}
result: