title: How to make SelectListItem Selected true or false on based on condition
body: <p>Here is my Model</p>
  
  <pre><code>  public class NewsViewModel
      {
          public NewsViewModel()
          {
  
              this.Categories = new List&lt;Category&gt;();
  
          }
          public int NewsId { get; set; }
          [Required(ErrorMessage = "Please enter News Title")]
          public string NewsTitle { get; set; }
          public IEnumerable&lt;Category&gt; Categories { get; set; }
  
  
      }
  </code></pre>
  
  <p>I need to set Selected to be True if id exists in NewsViewModel.Categories collection</p>
  
  <pre><code>private IEnumerable&lt;SelectListItem&gt; GetCategories()
  {
  
      return db.Categories .Select(s=&gt;new SelectListItem {
          Value=s.Id.ToString(),
          Text=s.Name,
          Selected = model.Categories.Select(x =&gt; x.CategoryId).Contains(s.CategoryId);
  
  }
  </code></pre>
  
  <p>And in View:</p>
  
  <pre><code>@Html.ListBoxFor(s =&gt; s.SelectedCategoriesIds, @Model.AllCategories, new { id = "DropDownList2", multiple = "multiple", @class = "form-control" })
  </code></pre>