Hidden input for Dictionary in ASP.NET MVC 3

Question

I need to get my model properties in Post action, so need to hidden element for them, but I have a problem with type of Dictionary <string, string>. this is My model:

public class ViewModel{
 ...
 public ViewPart ViewPart { get; set; }
}

public class ViewPart {
 ...
 public Dictionary<string, string> Flags { get; set; }
}

And My Controller:

Dictionary<string, string> flags = new Dictionary<string, string>();
flags.Add("kind", "Edit");
flags.Add("Command", "Save");
ViewModel model = new ViewModel(){ Flags  = flags };
return View(model);

In View:

@foreach(var item in Model.ViewPart.Flags) { 
 <input type="hidden" id="ViewPart_Flags_@(item.Key)" value="@item.Value" name="ViewPart.Flags[@(item.Key)]" />
}

Also I try This one :

@foreach(var item in Model.ViewPart.Flags) { 
  @Html.HiddenFor(modelItem => item)
}

Update Post Action:

[HttpPost]
public ActionResult MyPostAction(ViewModel model){
  //model.ViewPart.Flags is null
}

But in Post action the Flags is Always null, why? where is my fault? Is there any better way to pass variables from View To Action?

What does the Post action look like, does it receive the Flags model like `public ActionResult Something(ViewPart viewPart)`? — Garrett Fogerlie, Jul 07 '12 at 10:21

score 8 · Accepted Answer · answered Jul 07 '12 at 11:08

You need two hidden fields one for the Key and one for the Value if you want to modelbind to a dictionary:

var index = 0;
foreach (var item in Model.ViewPart.Flags)
{

    <input type="hidden" value="@item.Key" 
                         name="ViewPart.Flags[@(index)].Key"/>
    <input type="hidden" value="@item.Value" 
                         name="ViewPart.Flags[@(index)].Value"/>

    index++;
}
    <input type="submit" value="Save"/>

Note, you will be also need a running index to make the model binder happy.

Or if you don't want to have a running you can solve with an addtional hidden Index field:

foreach (var item in Model.ViewPart.Flags)
{

    <input type="hidden" value="@item.Key" 
                         name="ViewPart.Flags.Index"/>
    <input type="hidden" value="@item.Key" 
                         name="ViewPart.Flags[@(item.Key)].Key" />
    <input type="hidden" value="@item.Value" 
                         name="ViewPart.Flags[@(item.Key)].Value" />
}
    <input type="submit" value="Save"/>
}

You can find a lots of info about modelbinding with collections in this two article:

score 0 · Answer 2 · answered Jul 07 '12 at 10:52

Change your post action to this

[HttpPost]
public ActionResult MyPostAction(ViewModel model, ViewPart viewPart)
{
    model.ViewPart.Flags = viewPart.Flags;
}

and in the view use

@foreach(var item in Model.ViewPart.Flags) { 
  @Html.HiddenFor(modelItem => item)
}

If this doesn't work, check the source of the rendered HTML and see if the the Hidden information is rendered. I'm not sure if @Html.HiddenFor will work with a Dictionary you may need to write it out like you had done previously if it doesn't.

Hidden input for Dictionary in ASP.NET MVC 3

2 Answers2

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