Initializer syntax: new ViewDataDictionary { { "Name", "Value" } }

Question

I was searching for a way to pass ViewDataDictionary to a partial view in ASP.NET MVC that I came to this syntax:

new ViewDataDictionary { { "Name", "Value" } } 

I'm a bit confused about the initializer syntax here. can anyone explain it to me?

Answer 1

ViewDataDictionary implements IDictionary<string, object>.

IDictionary<string, object> is essentially a collection of KeyValuePair<string, object>.

Your ViewDataDictionary initializer (outer curly braces) contains another set of curly braces that represents a KeyValuePair<string, object> initializer.

The reason this is possible is explained in this answer.

You can Add multiple items by comma separating the KeyValuePair<string, object> initializers:

var data = new ViewDataDictionary  {      { "Name", "Value" },      { "Name2", "Value2" }  }; 

Is the same as:

var data = new ViewDataDictionary  {      new KeyValuePair<string, object>("Name", "Value"),      new KeyValuePair<string, object>("Name2", "Value2")  }; 

Essentially, the inner curly braces are nice syntax for initializing KeyValuePair<string, object> objects.

Answer 2

I solved this using an extension method:

/// <summary> /// Use this extension method to create a dictionary or objects ///     keyed by their property name from a given container object /// </summary> /// <param name="o">Anonymous name value pair object</param> /// <returns></returns> public static Dictionary<string, object> ToDictionary(this object o) {     var dictionary = new Dictionary<string, object>();      foreach (var propertyInfo in o.GetType().GetProperties())     {         if (propertyInfo.GetIndexParameters().Length == 0)         {             dictionary.Add(propertyInfo.Name, propertyInfo.GetValue(o, null));         }     }      return dictionary; } 

And an Html Helper extension:

/// <summary> /// When viewData is null, we just return null.  Otherwise, we ///     convert the viewData collection to a ViewDataDictionary /// </summary> /// <param name="htmlHelper">HtmlHelper provided by view</param> /// <param name="viewData">Anonymous view data object</param> /// <returns></returns> public static ViewDataDictionary vd(this HtmlHelper htmlHelper, object viewData) {     if (viewData == null) return null;      IDictionary<string, object> dict = viewData.ToDictionary();      //We build the ViewDataDictionary from scratch, because the     //  object parameter constructor for ViewDataDictionary doesn't     //  seem to work...     ViewDataDictionary vd = new ViewDataDictionary();     foreach (var item in dict)     {         vd[item.Key] = item.Value;     }      return vd; } 

Use from a razor file as:

@Html.Partial("~/Some/Path.cshtml", Model, Html.vd(new { SomeKey = SomeObj }))