ASP.NET MVC View Model not binding on HTTP Post with DropDownList
Solution 1
Looks like it might be because of a difference between properties and variables as noted in this question. Add { get; set; }
to all variables that you want to bind. As noted in that question I think this is because of the way the default model binder uses reflection.
I have found it useful in the past to actually grab the ASP.NET MVC source code so that I can debug it and see what is going on.
Solution 2
There is another reason for view model is NULL :
- The name of model in action parameter be the same as one of view model's properties
Example:
Model:
public class NewBookPageView{
int blabla {get;set;}
Book NewBook {get;set;} //NewBook is the same as newBook in action parameter
}
controller:
[HttpPost]
public ActionResult AddNewBook(NewBookPageView newBook)//newBook is the same as NewBook in view
{
int temp = newBook.blabla;
temp++;
//...
}
Tip: Here same name means case insensitive (newBook is same as NewBook)
Tip: Faced in MVC3 and MVC4.
Solution 3
To model binding in View you should use strongly-typed-html-helpers
replace
@Html.DropDownList("CategoryParentId", new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" })
to:
@Html.DropDownListFor(model => model.CategoryParentId, new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" })
Related videos on Youtube
Danny Brady
Full Stack .NET Developer specialiasing in Umbraco CMS.
Updated on July 09, 2022Comments
-
Danny Brady almost 2 years
I am having an issue that when I post to a controller I lose binding and everything in my view model is NULL. Here is the code I am using:
View:
@model ArticleCategoryVm @using (@Html.BeginForm()) { @Html.HiddenFor(model => model.LanguageIdDisplayed) <label>Name: <span class="label label-important">Required</span></label> @Html.HmlValidationFor(model => model.CategoryName) @Html.TextBoxFor(model => model.CategoryName, new { maxlength = "255", placeholder = "Category Name", @class = "input-xlarge-fluid" }) <span class="help-block">The is the name of the category and how it appears on the site.</span> <label>Language: <span class="label label-important">Required</span></label> @Html.HmlValidationFor(model => model.LanguageId) @Html.DropDownList("LanguageId", new SelectList(@Model.Languages, "Value", "Text"), "Select language", new { @class="input-xlarge-fluid" }) <span class="help-block">This will be the language that the category is set too.</span> <label>Parent:</label> @Html.HmlValidationFor(model => model.CategoryParentId) @Html.DropDownList("CategoryParentId", new SelectList(@Model.CategoryParents, "Value", "Text"), new { @class = "input-xlarge-fluid" }) <span class="help-block">Allows you to group the category under another existing category.</span> <label>Moderator Email: <span class="label label-important">Required</span></label> @Html.HmlValidationFor(model => model.ModeratorEmail) @Html.TextBoxFor(model => model.ModeratorEmail, new { maxlength = "255", placeholder = "Email Address", @class = "input-xlarge-fluid" }) <span class="help-block">This is the moderator email for articles in this category.</span> <button type="submit" class="btn btn-duadua btn-small"><i class="icon-ok-3"></i> Add New Category</button> }
ViewModel:
public class ArticleCategoryVm : BaseLayoutVm { public int LanguageIdDisplayed; public List<ArticleCategoryItemVm> ArticleCategoryItemVms { get; set; } // Add Category Fields [Required] public string CategoryName; [EmailAttribute] [Required] public string ModeratorEmail; [Required] public int LanguageId; public int CategoryParentId; public List<SelectListItem> Languages { get; set; } public List<SelectListItem> CategoryParents { get; set; } }
Controller:
[HttpPost] public ActionResult Categories(ArticleCategoryVm vm) { // Code here if (ModelState.IsValid) { } ReDrawDropDowns(vm); return View(vm) }
Why is everything in my viewmodel NULL? I can see in using Chromes tools that in the post the values are being posted for the strings and ints... As a work around I have just done the following to get the code working:
Workaround Controller:
[HttpPost] public ActionResult Categories(int LanguageIdDisplayed, string CategoryName, string ModeratorEmail, int LanguageId, int CategoryParentId) { var vm = new ArticleCategoryVm() { CategoryName = CategoryName, LanguageIdDisplayed = LanguageIdDisplayed, ModeratorEmail = ModeratorEmail, LanguageId = LanguageId, CategoryParentId = CategoryParentId }; if (ModelState.IsValid) { } ReDrawDropDowns(vm); return View(vm) }
Thanks
-
Ste W almost 10 yearsI just got caught out by this one... seems to be a lot of hidden reserved words / rules with action parameter names... a few days ago I wanted to have a parameter called 'action' which broke my routing! Somewhere under the hood I assume it’s making an anonymous object like the route values anonymous object that turns these parameters into properties on that object so if you use a name like ‘controller’, ‘action’ etc. it screws things up.
-
Samurai Ken almost 9 yearsThis was driving me NUTS. Sometimes you don't see what's right in front of your eyes.
-
Jeremy Ray Brown over 7 yearsThis fix worked perfectly. It was driving me nuts too, since I clearly saw the data posted while monitoring the request.
-
Clark Kent over 2 yearsThank you very much. That worked... I've been struggling for 3 hours. :-(