StaticSelectTagHelper

Inherits: TagHelper HTML Target: <select>

StaticSelectTagHelper is the tag helper that powers static-for and static-items on <select> elements. It renders <option> and <optgroup> tags from a SelectListItem collection, honors authored child content, and resolves selection from the bound model value first.

This tag helper is used declaratively — apply the static-for attribute on a <select> inside a Razor template for a component inheriting from StaticSelect.

Namespace

TechGems.StaticComponents.Headless.TagHelpers

HTML Target Element

<select static-for="@Model.InputExpression" static-items="@Model.Items"></select>

Usage

@model PinesSelect

<select static-for="@Model.InputExpression"
        static-items="@Model.Items"
        disabled="@(Model.Disabled ? "disabled" : null)"
        class="…">
</select>

Public Properties

InputExpression

[HtmlAttributeName("static-for")]
public ModelExpression InputExpression { get; set; }

The outer ModelExpression — its .ModelExplorer.Model is expected to be another ModelExpression bound to the consumer’s actual property.

Items

[HtmlAttributeName("static-items")]
public List<SelectListItem> Items { get; set; } = new List<SelectListItem>();

The list of items rendered inside the <select>. Items that share a SelectListGroup reference are rendered together inside a single <optgroup> at the position of the group’s first occurrence.

Supported Model Types

Guid, string, int, long, short, byte, float, double, decimal, DateTime and their nullable counterparts. bool is not supported.

Behavior

When processed (ProcessAsync), the tag helper:

1. Validates the inner model type is supported (throws otherwise).
2. Sets name, id and the data-val-* attributes through StaticHeadlessUtils.
3. Determines whether the bound model value matches at least one item Value (formatted via FormatModelValue for invariant-culture comparison).
4. Walks Items in original order:
   • Ungrouped items render inline as <option> tags.
   • The first item of a group emits an opening <optgroup label="…">, followed by every item sharing that group reference, followed by </optgroup>. Subsequent occurrences of the same group reference are skipped.
   • Groups are compared by reference — two SelectListGroup instances with the same Name but distinct references render as separate <optgroup> blocks.
   • SelectListGroup.Disabled is rendered as disabled on the <optgroup>.
5. Appends any authored child content (e.g. a leading placeholder <option>) and writes the combined HTML to the <select>’s content.

Selection priority

Condition	Result
Model value matches one of the item Values	That item is selected; every SelectListItem.Selected flag is ignored.
Model value is null	Fall back to SelectListItem.Selected.
Model value does not match any item	Fall back to SelectListItem.Selected.

Error Conditions

Condition	Exception
Inner property is not one of the supported model types	ArgumentException

Related

• Headless Components — Feature guide.
• StaticSelect