.net – 优雅的foreach – 在Razor构建

{% for user in users %}
    <li>{{ user.username|e }}</li>
{% else %}
    <li><em>no user found</em></li>
{% endfor %}

@foreach (var user in users) {
    <li>@user.UserName</li>
}
@if (!users.Any()) {
    <li><em>no user found</em></li>
}

巩固Jamiec和Martin Booth的答案.我创建了以下扩展方法.它将IEnumerable作为第一个参数,然后使用两个委托来呈现文本.在Razor Views中,我们可以向Templated Delegates传递两个这样的参数.简而言之,这意味着您可以提供模板.所以这是扩展方法以及如何调用它：

public static HelperResult Each<TItem>(this IEnumerable<TItem> items,Func<TItem,HelperResult> eachTemplate,Func<dynamic,HelperResult> other)
    {
        return new HelperResult(writer =>
        {
            foreach (var item in items)
            {
                var result = eachTemplate(item);
                result.WriteTo(writer);
            }

            if (!items.Any())
            {
                var otherResult = other(new ExpandoObject());
                // var otherResult = other(default(TItem));
                otherResult.WriteTo(writer);
            }
        });
    }

并在剃刀视图中：

@Model.Users.Each(
    @<li>@item.Name</li>,@<li>
        <b>No Items</b>
     </li>
)

总而言之,非常干净.

更新实施评论中提出的建议.此扩展方法使用一个参数循环集合中的项并返回自定义HelperResult.在那个helperresult上,如果没有找到任何项目,可以调用Else方法传入模板委托.

public static class HtmlHelpers
{
    public static ElseHelperResult<TItem> Each<TItem>(this IEnumerable<TItem> items,HelperResult> eachTemplate)
    {
        return ElseHelperResult<TItem>.Create(items,eachTemplate);
    }
}

public class ElseHelperResult<T> : HelperResult
{
    private class Data
    {
        public IEnumerable<T> Items { get; set; }
        public Func<T,HelperResult> EachTemplate { get; set; }
        public Func<dynamic,HelperResult> ElseTemplate { get; set; }

        public Data(IEnumerable<T> items,Func<T,HelperResult> eachTemplate)
        {
            Items = items;
            EachTemplate = eachTemplate;
        }

        public void Render(TextWriter writer)
        {
            foreach (var item in Items)
            {
                var result = EachTemplate(item);
                result.WriteTo(writer);
            }

            if (!Items.Any() && ElseTemplate != null)
            {
                var otherResult = ElseTemplate(new ExpandoObject());
                // var otherResult = other(default(TItem));
                otherResult.WriteTo(writer);
            }
        }
    }

    public ElseHelperResult<T> Else(Func<dynamic,HelperResult> elseTemplate)
    {
        RenderingData.ElseTemplate = elseTemplate;
        return this;
    }

    public static ElseHelperResult<T> Create(IEnumerable<T> items,HelperResult> eachTemplate)
    {
        var data = new Data(items,eachTemplate);
        return new ElseHelperResult<T>(data);
    }

    private ElseHelperResult(Data data)
        : base(data.Render)
    {
        RenderingData = data;
    }

    private Data RenderingData { get; set; }
}

然后可以按如下方式调用它：

@(Model.Users
   .Each(@<li>@item.Name</li>)
   .Else(
        @<li>
            <b>No Users</b>
         </li>
        )
)