c# MVC Html helper + 表达式 + 去除丑陋

Question

我正在尝试使用以下语法从 IList 创建下拉列表:

@Html.DropDowntListFor(Model.VisitingAddresses, vistingAddress => vistingAddress.Id, vistingAddress => vistingAddress.Name)

这适用于以下代码:

public static IHtmlString DropDowntListFor
        <TModel>(this HtmlHelper htmlHelper, IList<TModel> list, Expression<Func<TModel, string>> value, Expression<Func<TModel, string>> text)
    {
        var dropdownName = value.Parameters.First().Name;

        var selectedListItem = new List<SelectListItem>();

        var values = list.AsQueryable().Select(value).ToList();
        var texts = list.AsQueryable().Select(text).ToList();

        int i;
        for (i = 0; i < values.Count; i++)
        {
            selectedListItem.Add(new SelectListItem
                                     {
                                        Value = values[i],
                                        Text = texts[i]
                                     });
        }

        return htmlHelper.DropDownList(dropdownName, selectedListItem);
    }

但是如您所见，上面的代码(在 htmlhelper 中)真的很难看，有人知道在 html 帮助程序中使用更漂亮的方式(在代码中)吗？

提前致谢。

Answer 1

你在找这样的东西吗？

public static IHtmlString DropDowntListFor<TModel>
    (this HtmlHelper htmlHelper, IList<TModel> list, 
     Expression<Func<TModel, string>> valueSelector, 
     Expression<Func<TModel, string>> textSelector)
{
    var dropdownName = valueSelector.Parameters.First().Name;

    Func<TModel, string> compiledValueSelector = valueSelector.Compile();
    Func<TModel, string> compiledTextSelector = textSelector.Compile();

    var selectedListItem = list.Select(x => new SelectListItem {
                                           Value = compiledValueSelector(x),
                                           Text = compiledTextSelector(x) })
                               .ToList();

    return htmlHelper.DropDownList(dropdownName, selectedListItem);
}

请注意，如果您不需要文本选择器作为表达式树，您可以进一步稍微简化它:

public static IHtmlString DropDowntListFor<TModel>
    (this HtmlHelper htmlHelper, IList<TModel> list, 
     Expression<Func<TModel, string>> valueSelectorExpression, 
     Func<TModel, string> textSelector)
{
    var dropdownName = valueSelector.Parameters.First().Name;

    var valueSelector = valueSelectorExpression.Compile();

    var selectedListItem = list.Select(x => new SelectListItem {
                                           Value = valueSelector(x),
                                           Text = textSelector(x) })
                               .ToList();

    return htmlHelper.DropDownList(dropdownName, selectedListItem);
}