POST json dictionary

Question

I\'m trying the following : A model with a dictionary inside send it on the first ajax request then take the result serialize it again and send it back to the controller.

Answer 1

I came across the same issue today and came up with a solution which doesn't require anything but registering a new model binder. It's a bit hacky but hopefully it helps someone.

    public class DictionaryModelBinder : IModelBinder
    {
        /// 

        /// Binds the model to a value by using the specified controller context and binding context.
        /// 
        /// 
        /// The bound value.
        /// 
        /// The controller context.The binding context.
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            if (bindingContext == null)
                throw new ArgumentNullException("bindingContext");

            string modelName = bindingContext.ModelName;
            // Create a dictionary to hold the results
            IDictionary result = new Dictionary();

            // The ValueProvider property is of type IValueProvider, but it typically holds an object of type ValueProviderCollect
            // which is a collection of all the registered value providers.
            var providers = bindingContext.ValueProvider as ValueProviderCollection;
            if (providers != null)
            {
                // The DictionaryValueProvider is the once which contains the json values; unfortunately the ChildActionValueProvider and
                // RouteDataValueProvider extend DictionaryValueProvider too, so we have to get the provider which contains the 
                // modelName as a key. 
                var dictionaryValueProvider = providers
                    .OfType>()
                    .FirstOrDefault(vp => vp.ContainsPrefix(modelName));
                if (dictionaryValueProvider != null)
                {
                    // There's no public property for getting the collection of keys in a value provider. There is however
                    // a private field we can access with a bit of reflection.
                    var prefixsFieldInfo = dictionaryValueProvider.GetType().GetField("_prefixes",
                                                                                      BindingFlags.Instance |
                                                                                      BindingFlags.NonPublic);
                    if (prefixsFieldInfo != null)
                    {
                        var prefixes = prefixsFieldInfo.GetValue(dictionaryValueProvider) as HashSet;
                        if (prefixes != null)
                        {
                            // Find all the keys which start with the model name. If the model name is model.DictionaryProperty; 
                            // the keys we're looking for are model.DictionaryProperty.KeyName.
                            var keys = prefixes.Where(p => p.StartsWith(modelName + "."));
                            foreach (var key in keys)
                            {
                                // With each key, we can extract the value from the value provider. When adding to the dictionary we want to strip
                                // out the modelName prefix. (+1 for the extra '.')
                                result.Add(key.Substring(modelName.Length + 1), bindingContext.ValueProvider.GetValue(key).AttemptedValue);
                            }
                            return result;
                        }
                    }
                }
            }
            return null;
        }
    }

The binder is registered in the Global.asax file under application_start

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        RegisterGlobalFilters(GlobalFilters.Filters);
        RegisterRoutes(RouteTable.Routes);

        ModelBinders.Binders.Add(typeof(Dictionary), new DictionaryModelBinder());
    }