How do I group HTML List Items in an ASP.NET MVC V

问题:

I have this code in a view

<ul>
    @foreach (var tag in Model)
    {
        <li><a href="/Post/Tag/@tag.Id">@tag.Name</a></li>
    }
</ul>

now I need to group List Items by its first character, like

A
 -Apple
 -Ant

C
 -Car

S
 -Sky
 -Sea
 -Sun

How can I achieve this?

回答1:

How can I achieve this?

Very easy. The answer, as in the 99.99% of the questions in the asp.net-mvc tag is always the same: use view models.

I assume that you have the following domain model:

public class Tag
{
    public int Id { get; set; }
    public string Name { get; set; }
}

So as always you start by defining a view model that will meet the requirements you want to implement in this view (which is grouping a list of Tag domain models by the first letter of their Name property and display a link):

public class TagViewModel
{
    public string Letter { get; set; }
    public IEnumerable<Tag> Tags { get; set; }
}

then you will obviously have a controller whose responsibility is to query your DAL layer in order to fetch the domain model, build a view model and finally pass this view model to the view:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        // Get the domain model
        var tags = new[]
        {
            // Guess this comes from a database or something
            new Tag { Id = 1, Name = "Apple" },
            new Tag { Id = 2, Name = "Ant" },
            new Tag { Id = 3, Name = "Car" },
            new Tag { Id = 4, Name = "Sky" },
            new Tag { Id = 5, Name = "Sea" },
            new Tag { Id = 6, Name = "Sun" },
        };

        // now build the view model:
        var model = tags.GroupBy(t => t.Name.Substring(0, 1)).Select(g => new TagViewModel
        {
            Letter = g.Key,
            Tags = g
        });

        return View(model);
    }
}

and finally a view:

@model IEnumerable<TagViewModel>

@foreach (var item in Model)
{
    <h2>@item.Letter</h2>
    <ul>
        @foreach (var tag in item.Tags)
        {
            <li>
                <!-- Please notice the usage of an HTML helper to generate
                     the anchor instead of the hardcoded url shown in your
                     question which is very bad
                -->
                @Html.ActionLink(
                    tag.Name, 
                    "Post", 
                    "Tag", 
                    new { id = tag.Id }, 
                    null
                )
            </li>
        }
    </ul>
}

which will obviously give the desired result:

So next time you encounter some difficulty or problem in ASP.NET MVC tell to yourself: I must use a view model. See, problem solved.