Asp.Net MVC3 - 如何创建动态DropDownList

Question

我发现了很多这方面的文章,但我仍然不知道如何做到这一点.我正在尝试创建自己的博客引擎,我有查看创建文章(我首先使用EF和代码),现在我必须填写应添加文章的类别数,但我想将其更改为名称为的dropdownlist类别.我的模型看起来如下:

public class Article
{
    public int ArticleID { get; set; }
    [Required]
    public string Title { get; set; }
    [Required]
    public int CategoryID { get; set; }
    public DateTime Date { get; set; }
    [Required()]
    [DataType(DataType.MultilineText)]
    [AllowHtml]
    public string Text { get; set; }
    public virtual Category Category { get; set; }
    public IEnumerable<SelectListItem> Categories { get; set; }
    public virtual ICollection<Comment> Comments { get; set; }
}
public class Category
{
    public int CategoryID { get; set; }
    [Required]
    public string Name { get; set; }
    public virtual ICollection<Article> Articles { get; set; }

}

我知道我必须使用Enum(或者我认为),但我不确定如何.我不知道我发现哪个教程最适合我.

---

编辑:

谢谢你的答案,但我找到了别的东西.我在尝试这个:

这是我的模特:

public class Article
{
    [Key]
    public int ArticleID { get; set; }

    [Display(Name = "Title")]
    [StringLength(30, MinimumLength = 5)]
    [Required]
    public string Title { get; set; }

    public DateTime Date { get; set; }

    public int CategoryID { get; set; }

    [Required()]
    [DataType(DataType.MultilineText)]
    [AllowHtml]
    public string Text { get; set; }

   public Category Category { get; set; }

    public virtual ICollection<Comment> Comments { get; set; }

    public IEnumerable<Category> Categories { get; set; }
}
public class Category
{
[Key]
    public int CategoryId { get; set; }
    [Required]
public string CategoryName { get; set; }
    public virtual ICollection<Article> Articles { get; set; }

}

这是我的控制器来创建文章:

public ActionResult Vytvorit()
{
    IEnumerable<Category> categories = GetCaregories();
    var view = View(new Article() { Categories = categories });
    view.TempData.Add("Action", "Create");

    return view;

}

private static IEnumerable<Category> GetCaregories()
{
    IEnumerable<Category> categories;
    using (BlogDBContext context = new BlogDBContext())
    {
        categories = (from one in context.Categories
                      orderby one.CategoryName
                      select one).ToList();
    }
    return categories;
}

private Category GetCategory(int categoryID)
{
        return db.Categories.Find(categoryID);
}
//
// POST: /Clanky/Vytvorit

[HttpPost]
public ActionResult Vytvorit(Article newArticle)
{

    try
    {
        if (newArticle.CategoryID > 0)
        {
            newArticle.Category = GetCategory(newArticle.CategoryID);
        }
        if (TryValidateModel(newArticle))
        {
                db.Articles.Add(newArticle);
                db.SaveChanges();
            return RedirectToAction("Index");
        }
        else
        {
            newArticle.Categories = GetCaregories();
            var view = View(newArticle);
            view.TempData.Add("Action", "Create");
            return view;
        }
    }
    catch
    {
        return View();

    }
}

这是我观点的一部分:

     @Html.DropDownListFor(model => model.CategoryID, new SelectList(Model.Categories,"CategoryID","CategoryName"))
        @Html.ValidationMessageFor(model => model.CategoryID)

我有NullReferenceExeption的问题,但我不知道为什么.我可以这样做吗？对我来说这看起来很容易.

Answer 1

你的模型看起来很奇怪.它包含诸如CategoryID并且Category看起来多余的属性.它还包含一个SelectListItem名为的集合属性Categories.那么,这是模型还是视图模型？它看起来很混乱.让我们假设它是一个模型.在这种情况下,它更像是这样的:

public class Article
{
    public int ArticleID { get; set; }

    [Required]
    public string Title { get; set; }

    public DateTime Date { get; set; }

    [Required()]
    [DataType(DataType.MultilineText)]
    [AllowHtml]
    public string Text { get; set; }

    public virtual Category Category { get; set; }

    public IEnumerable<Category> Categories { get; set; }

    public virtual ICollection<Comment> Comments { get; set; }
}

public class Category
{
    public int CategoryID { get; set; }

    [Required]
    public string Name { get; set; }

    public virtual ICollection<Article> Articles { get; set; }

}

现在模型很清楚,我们可以定义一个将传递给视图的视图模型.视图模型是专门为视图设计的类.因此,根据您打算在此视图中放置的内容,您可以在此视图模型中定义它.到目前为止,你只谈到了下拉,所以让我们这样做:

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

然后我们有一个控制器:

public class ArticlesController: Controller
{
    private readonly IArticlesRepository _repository;
    public ArticlesController(IArticlesRepository repository)
    {
        _repository = repository;
    }

    public ActionResult Index()
    {
        Article article = _repository.GetArticle();
        ArticleViewModel viewModel = Mapper.Map<Article, ArticleViewModel>(article);
        return View(viewModel);
    }
}

因此,控制器使用存储库来获取模型,将其映射到视图模型(在此示例中,我使用AutoMapper)并将视图模型传递给视图,该视图将负责显示它:

@model AppName.Models.ArticleViewModel
@using (Html.BeginForm())
{
    @Html.DropDownListFor(
        x => x.SelectedCategoryId, 
        new SelectList(Model.Categories, "Value", "Text"),
        "-- Select category --"
    )
    <input type="submit" value="OK" />
}