Create a new AnonymousType instance

问题

I'm trying to create an AnonymousType instance looks like:

new { Channel = g.Key.Channel, Comment = g.Key.Comment, Count = g.Count() }

On the dark, .NET creates an AnonymousType with a constructor that takes three arguments: String, String, Int32.

In order to create a new instance of this anonymous type, T, I do:

object[] args = new object[3];
args[0] = "arg1";
args[1] = "arg2";
args[2] = 200;
(T)Activator.CreateInstance(typeof(T), args);

.NET dumps me:

Additional information: Constructor not found in '<>f__AnonymousType2`3[[System.String, ...],[System.String, ...],[System.Int32, ...]]'.

I don't know why CreateInstance is trying to call a constructor like [[],[],[]]!

Scope

The real scope is a bit more hard to explain:

I've created a Linq provider. This provider translates Linq sentences to my server methods. When I receive json information I need to project this information to whichever Type user has specified. In this case:

var enumerable = UIContainer.UIController.Instance.getDigitalInputs()
    .GroupBy(di => new { Channel = di.Channel, Comment = di.Comment })
    .Select(g => new { Channel = g.Key.Channel, Comment = g.Key.Comment, Count = g.Count() });

So, I need to project each json item to a new { Channel = g.Key.Channel, Comment = g.Key.Comment, Count = g.Count() }). At the end I need to create an instance of this anonymous type.

So:

// make the HTTP request
IRestResponse response = (IRestResponse) this.client.CallApi(path, Method.GET, queryParams, postBody, headerParams, formParams, fileParams, authSettings);

if (((int)response.StatusCode) >= 400) {
    throw new ApiException (response.StatusCode, "Error calling Search: " + response.Content, response.Content);
}

Newtonsoft.Json.Linq.JArray feeds = Newtonsoft.Json.Linq.JArray.Parse(response.Content);
if (feeds.Any())
{
     PropertyDescriptorCollection dynamicProperties = TypeDescriptor.GetProperties(feeds.First());
     foreach (dynamic feed in feeds)
     {
         object[] args = new object[dynamicProperties.Count];
         int i = 0;
         foreach (PropertyDescriptor prop in dynamicProperties)
         {
             args[i++] = prop.GetValue(feed);
         }
         //args[0] = "";
         //args[1] = "";
         //args[2] = 2;

         yield return (T)Activator.CreateInstance(typeof(T), args);
    }
}

回答1:

Not sure where you obtain T, but the code works fine if you use the anonymous type from the previous variable:

var x = new { Channel = "Channel", Comment = "Comment", Count = 1 };

object[] args = new object[3];
args[0] = "arg1";
args[1] = "arg2";
args[2] = 200;
var y = Activator.CreateInstance(x.GetType(), args);

(And in to reply to Luaan: .NET uses a constructor for anonymous types, see the IL:)

.method public hidebysig specialname rtspecialname 
        instance void  .ctor(!'<Channel>j__TPar' Channel,
                             !'<Comment>j__TPar' Comment,
                             !'<Count>j__TPar' Count) cil managed

来源：https://stackoverflow.com/questions/36908078/create-a-new-anonymoustype-instance

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