View returns null model

Question

I'm fairly new to working with ASP.NET MVC and I'm currently trying to solve a problem I just can't get my head around:

I'm trying to load a currentArea from my Database and create a CurrentArea object from it like this:

  //My view ("PlayGame")
 @model SE2_S2P2_opdracht.Models.CurrentArea     

<html>
<body>    
<div style="position:absolute; margin-top:8%; background-color:dimgrey; border:solid thin; border-color:darkgrey; width:59.45%; height:20%; opacity: 0.9">
 @if (Model.area.GoNorth(Model.area.NorthMap))
      {
            using (Html.BeginForm("NextArea", "Game", new { direction = "North" }, FormMethod.Post))
            {

            <div style="position:absolute;top:8%; left:7%;">

                @Html.HiddenFor(m => m.area)
                @Html.HiddenFor(m => m.player)
                <input id="submit" type="submit" value="Go North" class="btn" />
            </div>
            }
        }
</div>    
</body>
</html>

So when I press the Go North button it should trigger this:
(In summary: it should load a new CurrentArea based on the view-passed currentArea)

//My Controller ("GameController")
    public ActionResult NextArea(CurrentArea currentarea, string direction)
    {

        if (direction == "North")
        {
            return View("PlayGame", currentarea = new CurrentArea(AreaRepo.GetByNorthMap(currentarea.area), currentarea.player));
        }

After pressing the button I get a null reference saying that my CurrentArea (passed to the controller) is null. It does, however, read my direction string.

My CurrentArea Class is just a wrapper

public class CurrentArea
{
    public Area area { get; set; }
    public Player player { get; set; }
    public Enemy enemy { get; set; }

    public CurrentArea()
    {

    }

    public CurrentArea(Area area, Player player)
    {
        this.area = area;
        this.player = player;
    }

I made sure all required class properties had "{get; set;}" on them as well. (The ones I use in the required constructors, at least)

I suppose I'm missing something which more experienced programmers can instantly spot. (by using the @html.hiddenfor() I can pass certain class objects/properties without showing them, right?)

The debugger showed that all of my "CurrentArea" properties returned as a null. The issue is resolved now, though. :) — R. Filippini, Jan 24 '17 at 18:15

score 1 · Accepted Answer · edited May 23 '17 at 11:45

@Html.HiddenFor renders exactly one <input type="hidden"/>.

So if you want to post a complex object, make sure you render hidden fields for all properties of this object that shall be posted back. I don't know how your Area object looks like, but something along these lines:

@model CurrentArea 

@* post back the properties of CurrentArea.area we are interested in *@
@Html.HiddenFor(m => m.area.Name)
@Html.HiddenFor(m => m.area.Id)
@Html.HiddenFor(m => m.area.Coordinates.X)

@* post back the properties of CurrentArea.player ... *@
@Html.HiddenFor(m => m.player.Name)

See also Extend hiddenfor templates in asp net mvc.

That fixed the problem for me. Thinking about it like that also sounds very logical in hindsight. Thanks you for helping me out! — R. Filippini, Jan 24 '17 at 18:13

View returns null model

1 Answers1