Adding default tag ('asp-for') in custom tag helper

Question

Please help me to add default tag ('asp-for') in custom tag helper for checkboxlist. I want to use the tag like default.

Tag helper:

 [HtmlTargetElement(Attributes = "asp-checklistbox, asp-modelname")]
public class CheckListBoxTagHelper : TagHelper
{
    [HtmlAttributeName("asp-checklistbox")]
    public IEnumerable<SelectListItem> Items { get; set; }

    [HtmlAttributeName("asp-modelname")]
    public string ModelName { get; set; }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {


        var i = 0;
        foreach (var item in Items)
        {
            var selected = item.Selected ? @"checked=""checked""" : "";
            var disabled = item.Disabled ? @"disabled=""disabled""" : "";

            var html = $@"<label><input type=""checkbox"" {selected} {disabled} id=""{ModelName}_{i}__Selected"" name=""{ModelName}[{i}].Selected"" value=""true"" /> {item.Text}</label>";
            html += $@"<input type=""hidden"" id=""{ModelName}_{i}__Value"" name=""{ModelName}[{i}].Value"" value=""{item.Value}"">";
            html += $@"<input type=""hidden"" id=""{ModelName}_{i}__Text"" name=""{ModelName}[{i}].Text"" value=""{item.Text}"">";

            output.Content.AppendHtml(html);

            i++;
        }

        output.Attributes.SetAttribute("class", "th-chklstbx");
    }

}

View:

 <div asp-checklistbox="workTypeList" asp-modelname="workTypeId" asp-for="workTypeId"></div>

Answer 1

You can mimic asp-for implementation from standard helpers.

Mark your tag helper with [HtmlTargetElement("mychecklistbox", Attributes = "asp-for")] and add to your CheckListBoxTagHelper class this property:

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

And use this For property for output HTML you need to access the Model detail like Name. See standard helpers which use it - e.g. LabelTagHelper or others.