Remove blank entry from EnumDropDownListFor(…)?

问题

I found a few S.O. posts regarding this problem, but none of the accepted answers worked for me. I am using an enum to create an EnumDropDownListFor and it's working, but I do not want a blank entry at the top of the drop-down. I want the user to be forced to accept one of the items from the enum. Code follows:

@Html.EnumDropDownListFor(m => m.Foo, new { @class = "input-block-level " + Model.FooThingType, autocomplete = "off", style = "width: 100px;" })

Note on the above, I have tried several variants of this based on the accepted answers in other S.O. posts, including adding and removing a variety of arguments in the EnumDropDownListFor(...) call. This results only in compile time errors, mostly "no version of EnumDropDownListFor() takes n arguments" errors. E.g.:

@Html.EnumDropDownListFor(m => m.Foo, null, new { @class = "input-block-level " + Model.FooThingType, autocomplete = "off", style = "width: 100px;" })

... or ...

@Html.EnumDropDownListFor(m => m.Foo, "whatever", new { @class = "input-block-level " + Model.FooThingType, autocomplete = "off", style = "width: 100px;" })

The enum itself:

public enum SomeEnum
{
    [Description("Thingie")]
    Thingie,

    [Description("AnotherThingie")]
    AnotherThingie,

    [Description("LastThingie")]
    LastThingie
}

I also tried this, but it made no difference:

public enum SomeEnum
{
    [Description("Thingie")]
    Thingie = 0,

    [Description("AnotherThingie")]
    AnotherThingie = 1,

    [Description("LastThingie")]
    LastThingie = 2
}

回答1:

You have not shown you model, but clearly your property is nullable, i.e.

public SomeEnum? Foo { get; set }

which allows null values, therefore the EnumDropDownListFor() method generates a null option so that it can be selected.

You can either make the property not nullable (which will remove the null option)

public SomeEnum Foo { get; set }

or better, leave it nullable and add the [Required] attribute to force the user to make a selection which protects against under-posting attacks (refer What does it mean for a property to be [Required] and nullable? for a detailed explanation)

[Required(ErrorMessage = "Please select a ... ")]
public SomeEnum Foo { get; set }

and in the view add

@Html.EnumDropDownListFor(m => m.Foo, new { ... })
@Html.ValidationMessageFor(m => m.Foo)

来源：https://stackoverflow.com/questions/48269607/remove-blank-entry-from-enumdropdownlistfor

标签

asp.net-mvc

enums

html-helper