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?
asked Sep 4, 2013 at 7:45
Mahmood Dehghan Tazereh
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1MSDN on collection initializers in C# and VBKyleMit– KyleMit ♦2016-11-21 15:41:11 +00:00Commented Nov 21, 2016 at 15:41
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2 Answers
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.
2 Comments
Mahmood Dehghan Tazereh
Are items in
IDictionary<string, object> of type KeyValuePair<string, object>?
Oliver
@Mahmoodvcs yes,
IDictionary<string, object> is essentially a collection of KeyValuePair<string, object>.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 }))
