dropdownlist set selected value in MVC3 Razor

问题

Here is my model:

public class NewsCategoriesModel {
    public int NewsCategoriesID { get; set; }        
    public string NewsCategoriesName { get; set; }
}

My controller:

public ActionResult NewsEdit(int ID, dms_New dsn) {
    dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();
    var selectedValue = dsn.NewsCategoriesID;
    SelectList ListCategories = new SelectList(categories, "NewsCategoriesID", "NewsCategoriesName",selectedValue);

    // ViewBag.NewsCategoriesID = new SelectList(categories as IEnumerable<dms_NewsCategory>, "NewsCategoriesID", "NewsCategoriesName", dsn.NewsCategoriesID);
    ViewBag.NewsCategoriesID = ListCategories;
    return View(dsn);
}

And then my view:

@Html.DropDownList("NewsCategoriesID", (SelectList)ViewBag.NewsCategoriesID)

When i run, the DropDownList does not select the value I set.. It is always selecting the first option.

回答1:

You should use view models and forget about ViewBag Think of it as if it didn't exist. You will see how easier things will become. So define a view model:

public class MyViewModel
{
    public int SelectedCategoryId { get; set; }
    public IEnumerable<SelectListItem> Categories { get; set; } 
}

and then populate this view model from the controller:

public ActionResult NewsEdit(int ID, dms_New dsn)
{
    var dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();

    var model = new MyViewModel
    {
        SelectedCategoryId = dsn.NewsCategoriesID,
        Categories = categories.Select(x => new SelectListItem
        {
            Value = x.NewsCategoriesID.ToString(),
            Text = x.NewsCategoriesName
        })
    };
    return View(model);
}

and finally in your view use the strongly typed DropDownListFor helper:

@model MyViewModel

@Html.DropDownListFor(
    x => x.SelectedCategoryId,
    Model.Categories
)

回答2:

just in case someone comes with this question, this is how I do it, please forget about the repository object, I'm using the Repository Pattern, you can use your object context to retrieve the entities. And also don't pay attention to my entity names, my entity type Action has nothing to do with an MVC Action.

Controller:

ViewBag.ActionStatusId = new SelectList(repository.GetAll<ActionStatus>(), "ActionStatusId", "Name", myAction.ActionStatusId);

Pay attention that the last variable of the SelectList constructor is the selected value (object selectedValue)

Then this is my view to render it:

<div class="editor-label">
   @Html.LabelFor(model => model.ActionStatusId, "ActionStatus")
</div>
<div class="editor-field">
   @Html.DropDownList("ActionStatusId")
   @Html.ValidationMessageFor(model => model.ActionStatusId)
</div> 

I think it is pretty simple, I hope this helps! :)

回答3:

I drilled down the formation of the drop down list instead of using @Html.DropDownList(). This is useful if you have to set the value of the dropdown list at runtime in razor instead of controller:

<select id="NewsCategoriesID" name="NewsCategoriesID">
    @foreach (SelectListItem option in ViewBag.NewsCategoriesID)
    {
        <option value="@option.Value" @(option.Value == ViewBag.ValueToSet ? "selected='selected'" : "")>@option.Text</option>

    }
</select>

回答4:

Well its very simple in controller you have somthing like this:

-- Controller

ViewBag.Profile_Id = new SelectList(db.Profiles, "Id", "Name", model.Profile_Id);

--View (Option A)

@Html.DropDownList("Profile_Id")

--View (Option B) --> Send a null value to the list

@Html.DropDownList("Profile_Id", null, "-- Choose --", new {  @class = "input-large" })

回答5:

Replace below line with new updated working code:

@Html.DropDownList("NewsCategoriesID", (SelectList)ViewBag.NewsCategoriesID)

Now Implement new updated working code:

@Html.DropDownListFor(model => model.NewsCategoriesID, ViewBag.NewsCategoriesID as List<SelectListItem>, new {name = "NewsCategoriesID", id = "NewsCategoriesID" })

回答6:

I want to put the correct answer in here, just in case others are having this problem like I was. If you hate the ViewBag, fine don't use it, but the real problem with the code in the question is that the same name is being used for both the model property and the selectlist as was pointed out by @RickAndMSFT

Simply changing the name of the DropDownList control should resolve the issue, like so:

@Html.DropDownList("NewsCategoriesSelection", (SelectList)ViewBag.NewsCategoriesID)

It doesn't really have anything to do with using the ViewBag or not using the ViewBag as you can have a name collision with the control regardless.

回答7:

I prefer the lambda form of the DropDownList helper - see MVC 3 Layout Page, Razor Template, and DropdownList

If you want to use the SelectList, then I think this bug report might assist - http://aspnet.codeplex.com/workitem/4932

回答8:

code bellow, get from, goes

Controller:

int DefaultId = 1;
ViewBag.Person = db.XXXX
        .ToList()
        .Select(x => new SelectListItem {
            Value = x.Id.ToString(),
            Text = x.Name,
            Selected = (x.Id == DefaultId)
        });

View:

@Html.DropDownList("Person")

Note: ViewBag.Person and @Html.DropDownList("Person") name should be as in view model

回答9:

To have the IT department selected, when the departments are loaded from tblDepartment table, use the following overloaded constructor of SelectList class. Notice that we are passing a value of 1 for selectedValue parameter.

ViewBag.Departments = new SelectList(db.Departments, "Id", "Name", "1");

回答10:

For anyone that dont want to or dont make sense to use dropdownlistfor, here is how I did it in jQuery with .NET MVC set up.

1. Front end Javascript -> getting data from model:

    var settings = @Html.Raw(Json.Encode(Model.GlobalSetting.NotificationFrequencySettings)); 

    SelectNotificationSettings(settings);

    function SelectNotificationSettings(settings) {
                $.each(settings, function (i, value) {
                    $("#" + value.NotificationItemTypeId + " option[value=" + value.NotificationFrequencyTypeId + "]").prop("selected", true);
                });
    }

2. In razor html, you going to have few dropdownlist

 @Html.DropDownList(NotificationItemTypeEnum.GenerateSubscriptionNotification.ToString,
    notificationFrequencyOptions, optionLabel:=DbRes.T("Default", "CommonLabels"),
    htmlAttributes:=New With {.class = "form-control notification-item-type", .id = Convert.ToInt32(NotificationItemTypeEnum.GenerateSubscriptionNotification)})

And when page load, you js function is going to set the selected option based on value that's stored in @model.

Cheers.

来源：https://stackoverflow.com/questions/6807256/dropdownlist-set-selected-value-in-mvc3-razor