SelectList pulling info from ViewBag: not creating value=“…” in generated html

问题

I'm trying to create a client-side validated dropdown list in an MVC4 application using the Razor view engine.

The code in the view to generate the dropdown list is as follows:

 @Html.DropDownList("Test", new SelectList(ViewBag.AvailableLoBsDescriptions, ViewBag.AvailableLoBsIds), "--none--")

Note that ViewBag.AvailableLoBsDescriptions is created in the controller using an IList while ViewBag.AvailableLoBsIds is also created in the controller using an IList.

What I expected to happen is have Razor generate a dropdown menu where Descriptions populates the inner html of each while the Ids populates the value="...". However, there is nothing generated for value at all, resulting in something like this:

<select id="Test" name="Test"><option value="">--none--</option>
<option>N/A</option>
<option>aaaa</option>
<option>bbbb</option>
<option>cccc</option>
<option>dddd</option>
<option>eeee</option>
<option>ffff</option>
</select>

Looking at the SelectList documentation, http://msdn.microsoft.com/en-us/library/system.web.mvc.selectlist%28v=vs.108%29.aspx, it seems to me that this should work. Does anyone have an idea why the values are not being generated for anything other than the placeholder?

Thanks!

回答1:

The constructor you are using looks like the following:

SelectList(IEnumerable, Object)

The second parameter here dictates the currently selected object from the collection in the first parameter. It does not dictate an object to use as a list of values.

What you should be doing is using SelectList(IEnumerable, String, String). This allows you to pass the name of a property (of each element of IEnumerable) to use for the description and one for the value. You can then produce something like this:

Controller:

// Create your IEnumerable
var LoBs = new List<LoB>();

// Assign some parameters to your objects
var exampleItem = new LoB();
exampleItem.Description = "Option text";
exampleItem.Value = "myValue";

// Populate your list and return your view.
LoBs.Add(exampleItem);
ViewBag.LoBs = LoBs;
return View();

View:

@Html.DropDownList("Test",
    new SelectList(ViewBag.LoBs, "Value", "Description"),
    "--none--")

Et voila...

<select id="Test" name="Test">
    <option value="">--none--</option>
    <option value="myValue">Option text</option>
</select>

来源：https://stackoverflow.com/questions/15841388/selectlist-pulling-info-from-viewbag-not-creating-value-in-generated-html

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ASP.NET

razor

drop-down-menu

selectlist