Html.EnumDropDownListFor根据枚举变量的值设置选定的列表项 [英] Html.EnumDropDownListFor Set selected listitem based on enum variable's value

问题描述

这可能是重复的，所以我已经指出了我从该站点上的阅读可以让我取得一些进步...

This may be a duplicate, so I have indicated where my reading from this site has allowed me some progress...

我有一个定义如下的模型:

I have a model defined as follows:

public enum RequestType
{
    [Display(Name = "Lovely Cold Beer")]
    Beer = 0,
    [Display(Name = "Warm Tea")]
    Tea = 1,
    [Display(Name = "Milky Coffee")]
    Coffee= 2
}

基于URL，我有一个变量，该变量将用于自动选择适当的列表项，例如

Based on the URL, I have a variable that will be used to automatically select the appropriate list item, e.g.

http://example.com/Request/Tea

将在控制器中执行此操作...

will do this in the controller...

ViewBag.RequestType = RequestType.Tea.ToString();
return View("Index");

在我看来，我有一个变量可以读回该值，然后显示适当的内容:

In my view I have a variable to read this value back, which then displays appropriate content:

if (ViewBag.RequestType != null)
{
    reqType = Enum.Parse(typeof(RequestType), ViewBag.RequestType);
}

在此视图中，我使用以下命令创建一个下拉列表:

In this view I create a drop down list using:

@Html.EnumDropDownListFor(model => model.RequestType, htmlAttributes: new { @onchange = "YadaYada();" })

这将使用为每个Enum定义的Display Name值呈现列表.我需要的是在呈现页面时自动选择合适的列表项，该列表项与reqType的值匹配.

This renders the list using the Display Name values defined for each Enum. What I need is to automatically select the appropriate list item when the page is rendered, that matches the value of reqType.

从我的研究中，我可以像这样传递变量:

From my research I see that I can pass in the variable like so:

@Html.EnumDropDownListFor(model => model.RequestType, reqType.ToString(), htmlAttributes: new { @onchange = "YadaYada();" })

但这会创建一个新列表项，其中包含枚举值而不是显示名称，例如

But this creates a new list item containing the enum value and not the display name, e.g.

Tea <-- This should not be created, instead 'Warm Tea' should be selected
Lovely Cold Beer
Warm Tea
Milky Coffee

由于我是MVC的新手，所以我的整个方法可能是错误的，但是欢迎提出建议以解决此问题！我不明白为什么在控制器中，对枚举值使用ToString会产生与在EnumDropDownListFor方法中执行相同操作的结果不同的结果.

My entire approach may be wrong as I'm new to MVC, but I'd welcome advice to fix it please! I don't understand why in the controller, using ToString on the enum value creates a different outcome to doing the same in the EnumDropDownListFor method.

推荐答案

您的EnumDropDownListFor()方法的第二个参数(reqType.ToString())使用的是

The second parameter (reqType.ToString()) of your EnumDropDownListFor() method is using the overload which adds an optionLabel (an option with a null value used for validation). It does not set the value of the selected option.

MVC的模型绑定功能通过绑定到属性来工作，并且由于RequestType的默认值为"Beer"，因此将选择该选项.

Model binding features of MVC work by binding to your property and since the default value of your RequestType is "Beer" , then that option will be selected.

例如，您需要在将模型传递到视图之前设置模型中属性的值(假设您具有/Request/{request}的特定路线)

You need to set the value of the property in the model before you pass the model to the view, for example (assumes you have a specific route for /Request/{request})

public ActionResult Request(RequestType request)
{
    var model = new MyModel
    {
        RequestType = request
    };
    return View(model);
}

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