How to read properties from anonymous types using "dynamic" variable

Question

I had the cunning idea of using a dynamic variable to test the results of a method that returns an anonymous type - more specifically it returns a JsonResult, which as json looks like this

{ "newData" : [ 1120741.2697475906,
      826527.64681837813
    ],
  "oldData" : [ 1849870.2326665826,
      1763440.5884212805
    ],
  "timeSteps" : [ 0,
      4.8828124999999998e-10
    ],
  "total" : 2
}

I can read the JSonResult which will give me the anonymous type. Here's my code:

var jsonResult = controller.GetChangeData(1) as JsonResult;
dynamic data = jsonResult.Data;
Assert.AreEqual(2, data.total); // This works fine :)

But how do I get at "newData" for example? This code....

var newData = data.newData;

Gives me a System.Linq.Enumerable.WhereSelectArrayIterator, but I don't know what to do with it to be able to just use it as an arry of doubles.

I tried casting it as a double[], but it doesn't work either.

As an aside, can I easily check if a property is defined on the dynamic?

var data2 = data.newData.ToArray(); --- > 'object' does not contain a definition for 'ToArray' (tried with some casts too) — Matt Roberts
– Matt Roberts, Commented Nov 12, 2010 at 12:49

Gabe · Accepted Answer · 2010-11-14 00:56:38Z

3

The reason .ToArray() doesn't work is that it's an extension method, and extension methods aren't available at runtime. That just means you have to call the function statically. Does Enumerable.ToArray<double>(data.newData) work?

You may need Enumerable.ToArray(Enumerable.Cast<double>(data.newData)) depending on what elements newData actually has.

edited Nov 14, 2010 at 0:56

answered Nov 12, 2010 at 13:23

Gabe

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Matt Roberts Over a year ago

Yes! Enumerable.ToArray<double>(data.newData) does the job for me :) Thanks

Shiv Kumar · Accepted Answer · 2010-11-12 13:22:54Z

2

To get the properties of an instance of a dynamic type

PropertyDescriptorCollection props = TypeDescriptor.GetProperties(dyn);
foreach (PropertyDescriptor prop in props)
{
  object val = prop.GetValue(dyn);
  var propName = prop.Name;
  var propValue = val;
}

where dyn is an instance of a dynamic object.

edited Nov 12, 2010 at 13:22

answered Nov 12, 2010 at 13:17

Shiv Kumar

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Bryan B Over a year ago

This was a helpful copy+pastable nugget of code, that I'm pretty sure is going to become an extension method at work...

Si Phillipson · Accepted Answer · 2010-11-12 13:25:06Z

1

Could you use the JavaScriptSerializer class to parse the Json string into a dynamic variable? Eg:

var serializer = new JavaScriptSerializer();
var jsonObj = serializer.Deserialize<dynamic>(jsonString);
var newData1 = jsonObj["newData"][0];

answered Nov 12, 2010 at 13:25

Si Phillipson

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1 Comment

Matt Roberts Over a year ago

+1 for a working answer. The prob with this is since my json was in a JsonResult, I needed to Serialize it to a string and then deserialize it back into a dynamic, so less ideal.

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