c# - 将默认选项添加到 SelectList - MVC3 C#

Question

我需要在我的选择列表中添加一个选项，例如：

<option value="">Select an Option Below</option>

这是我生成选择列表的方法：

不确定在哪里添加此选项。谢谢

public static IEnumerable<SelectListItem> GetBuildingClubs(List<BuildingClub> localClubs, List<BuildingClub> psfyClubs)
{
    var buildingClubList = new List<SelectListItem>();
    IEnumerable<BuildingClub> allBuildingClubs = localClubs.Union(psfyClubs);
    foreach (BuildingClub b in allBuildingClubs)
    {
        buildingClubList.Add(new SelectListItem
        {
            Value = b.MasterCustomerId,
            Text = b.NewBuildingClubName

        });
    }

    buildingClubList.OrderBy(c => c.Text);
    //Prepend the default option here???
    return buildingClubList;
}

Answer 1

无需在集合中添加默认值，您可以直接在视图中执行此操作：

@Html.DropDownListFor(model => model.SelectedValue, Model.BuildingClubList, "Select an Option Below")

带有"Select an Option Below"空白值的项目将出现在您的下拉列表中。

假设您的模型包含一个由您的方法BuildingClubList初始化的属性。GetBuildingClubs

Answer 2

您可以使用Insert类似的方法

 buildingClubList.Insert(0, new SelectListItem
    {
        Value = "",
        Text = "Select an Option Below"

    });

或者

SelectListItem在循环之前添加默认值

Answer 3

对于未来的用户（我知道这很旧，但我自己在寻找解决方案时遇到了它），如果您有一个具有单个选定值的现有 SelectList，那么这个助手将为您提供 Add 和 Prepend 方法：-

/// <summary>
/// A static helper class providing extension methods to SelectList instances
/// </summary>
public static class SelectListExtensions
{
    /// <summary>
    /// Adds the specified value to the select list.
    /// </summary>
    /// <param name="selectList">The select list.</param>
    /// <param name="value">The value.</param>
    /// <param name="text">The text.</param>
    /// <param name="selected">if set to <c>true</c> [selected].</param>
    /// <returns>The modified/rebuilt select list</returns>
    public static SelectList Add(this SelectList selectList, string value, string text, bool selected = false)
    {
        var itemList = selectList.ToList().FluentAdd(
            new SelectListItem { Value = value, Text = text, Selected = selected }
        );
        return new SelectList(itemList, "Value", "Text");
    }
    /// <summary>
    /// Prepends the specified value to the select list.
    /// </summary>
    /// <param name="selectList">The select list.</param>
    /// <param name="value">The value.</param>
    /// <param name="text">The text.</param>
    /// <param name="selected">if set to <c>true</c> [selected].</param>
    /// <returns>The modified/rebuilt select list</returns>
    public static SelectList Prepend(this SelectList selectList, string value, string text, bool selected = false)
    {
        var itemList = selectList.ToList();
        itemList.Insert(0, new SelectListItem { Value = value, Text = text, Selected = selected });
        return new SelectList(itemList, "Value", "Text", selectList.SelectedValue);
    }
}

Answer 4

只需添加一个

buildingClubList.Add(new SelectListItem
{
    Value = "",
    Text = "Select an Option Below"
});

在你的 foreach 循环之前。

Answer 5

在进入你的 foreach 循环之前，添加：

buildingClubList.Add(new SelectListItem
        {
            Value = "",
            Text = "Select an Option Below"

        });

在他们选择某些东西后，您当然要验证它不是这个选项

Answer 6

这是旧的，如果您想要“提示”选项，@RédaMattar 的答案是最好/正确的答案，但我偶然发现它希望手动向 SelectList 添加一个有价值的选项（例如 - 一个允许客户端触发“新" 行动) 这似乎是最干净的方式：

 selectList = selectList.Prepend(
                 new SelectListItem { Value = "New", Text = "New", Selected = false }
              );