从EnumDropDownListFor（...）删除空白条目？

问题描述

我找到了一些S.O.有关此问题的帖子，但没有一个对我有用的答案。我正在使用枚举创建一个 EnumDropDownListFor ，它正在工作，但我不想在顶部输入空白的下拉菜单。我希望用户被迫接受枚举中的一项。代码如下：

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;" })

注意上述内容，我已经根据其他方法中的公认答案尝试了几种方法帖子，包括在 EnumDropDownListFor（...）调用中添加和删除各种参数。这只会导致编译时错误，主要是没有EnumDropDownListFor（）版本使用 n 自变量错误。例如：

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;" })

...或...

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

枚举本身：

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

    [Description("AnotherThingie")]
    AnotherThingie,

    [Description("LastThingie")]
    LastThingie
}

我也尝试过此操作，但是没什么区别。

I also tried this, but it made no difference:

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

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

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

推荐答案

您尚未显示模型，但显然您的资产为空，即

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

public SomeEnum? Foo { get; set }

允许 null 值，因此 EnumDropDownListFor（）方法生成一个 null 选项，以便可以选择它。

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

您可以使属性不可为空（这将删除 null 选项）

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

public SomeEnum Foo { get; set }

或更好，将其保留为空并添加 [Required] 属性可强制用户进行选择，以防止发布不足的攻击（请参阅以获取详细说明）

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 }

并在视图中添加

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

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