Why is using GetEnumSelectList mandatory?

Question

Why do I have to specify the items for a select control targeting an enumerated value explicitly? I would expect the tag helper to populate it for me.

Answer 1

Because it only knows the values, not the text.

Answer 2

The control is bound to a field of an enumerated type. The renderer can examine the type and extract the values from it.

I understand your point but the tag helpers don't work that way. The asp-for tag helper maps the HTML input name to the model property name. This is used in model binding. The asp-items tag helper expects a collection of SelectListItem which is used to render the select options. The Html.GetEnumSelectList is a convenient way to convert an enumeration (named constant) to a IEnumerable<SelectListItem>.

Similarly, you can use the SelectList(IEnumerable, String, String) constructor to populate select options from a custom collection.

Answer 3

Hi @Krzysztof Żelechowski ,

The Built-in ASP.NET Core Tag Helpers doesn't contain the specific tag helper to directly render the Enum (without using the <select> tag and the GetEnumSelectList method). If you expect the tag helper for the enum type, you could submit feedback at the end of the tag helpers document.

It's often convenient to use <select> with an enum property and generate the SelectListItem elements from the enum values. The GetEnumSelectList method generates a SelectList object for an enum. More detail information, see: Enum binding

If you don't want to use the <select> tag, you can try to create a custom tag helper to display the enum. Refer to the following articles:

Create Tag Helpers

Creating Custom Tag Helpers With ASP.NET Core MVC

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Best regards,
Dillion

Answer 4

the select tag helper is used to generate the select.

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.taghelpers.selecttaghelper?view=aspnetcore-6.0

the asp-for sets the binding string via an expression tree. this is just a syntax tree, and the datatype is not specified
the asp-items is used to generate the options list. asp-items expects an IEnumable<SelectListItem>

there are a lot of helpers to generate Items (option list). one is the GetEnumSelectList, but there are others.

at render time, the only way for the tag helper to get the datatype is to bind to the model which may be null, making generic defaults difficult.