Question

Here is view models

public class ArticleViewModel 
    {
        public string ID { get; set; }
        public string Title{ get; set; }
        public string Body { get; set; }
        public List<BETag> TagsList { get; set; }

    }

public class  BETag  
    {
        public string ID { get; set; }
        public string Name { get; set; }
    }

An action

  [HttpPost, AuthorizeEx]
  public ActionResult  AddArticle(ArticleViewModel articleViewModel)
  {
      //articleViewModel.Tags.Count == 0 
      //Request.Form["TagsList"] == "tag1, tag2..."
  }

and a part of AddArticle.cshtml

@Html.TextAreaFor(m => m.TagsList )

My question is why articleViewModel.Tags.Count is equal 0, but
Request.Form["TagsList"] is equal "tag1, tag2..."? How to bind ArticleViewModel properly?

Answer 1

Lists don’t work that way in MVC. You need to use something like EditorFor(m => m.TagsList) and then you need to create a BETag EditorTemplate. But that’s only part of the problem, and really won’t work for you either.

What you really want is just a simple string that takes your list of tags, such as

public string TagListString {get;set;}

Then, in your controller, you parse the string and extract all your tags, then add them to the TagsList.

var tags = TagListString.Split(' '); // assumes only single space between tags, 
                                     // you should add more filtering to make sure

foreach(var tag in tags) {
    TagList.Add(new BETag() { Name = tag });
}

MVC works with single items, not complex types. There is some built-in processing to breakdown complex types in some cases, and to automatically iterate over collections, but those don’t work in your case because you want to edit all the items in a single field. So your only option is to parse the field in the post method and put the data where you want it.