JavaScriptSerializer: Object reference not set to an instance of an object

Question

What am I doing wrong here?

using System.Web.Script.Serialization;

string json = "{\"numbers\":[{\"one\":\"1\"},{\"two\":\"2\"},{\"three\":\"3\"}]}";
dynamic dictionary = new JavaScriptSerializer().Deserialize<dynamic>(json);
Assert.AreEqual(3, dictionary["numbers"].Count);

System.NullReferenceException : Object reference not set to an instance of an object
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToObject (IDictionary`2 dict, System.Type type) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToType (System.Type type, System.Object obj) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToList (System.Collections.ArrayList col, System.Type type) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToType (System.Type type, System.Object obj) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToObject (IDictionary`2 dict, System.Type type) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToType (System.Type type, System.Object obj) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToType[Object] (System.Object obj) [0x00000] in <filename unknown>:0 
  at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize[Object] (System.String input) [0x00000] in <filename unknown>:0

Just one thing that I don't get: why are you using the dynamic keyword there, it bring no benefit in your case. — MeTitus
– MeTitus, Commented May 8, 2013 at 0:02
and if you look at this line: "at System.Web.Script.Serialization.JavaScriptSerializer.ConvertToObject (IDictionary`2 dict, System.Type type) [0x00000] in <filename unknown>:0", the error seems to be related when converting to the dictionary. Did you try using the static type instead just to narrow the problem? — MeTitus
– MeTitus, Commented May 8, 2013 at 0:04

MeTitus · Accepted Answer · 2013-05-08 00:13:57Z

2

As I see no problems with your code, apart from the use of the count property, and since the code is breaking when the json is being deserialized, I would advise you to use the static type definition instead, just to narrow the changes of problems with your code:

        string json = "{\"numbers\":[{\"one\":\"1\"},{\"two\":\"2\"},{\"three\":\"3\"}]}";
        var dictionary = new JavaScriptSerializer().Deserialize<Dictionary<string, object>>(json);

Maybe just maybe there is an issue with using dynamic types with the JavaScriptSerializer and if there is indeed a problem with the JavaScriptSerializer you can always report that to MSFT.

answered May 8, 2013 at 0:13

MeTitus

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4 Comments

Tiago Fernandez Over a year ago

Using <Dictionary<string, object>> over dynamic still gives me the same error :(

MeTitus Over a year ago

I tried that code myself and if does work properly, and even if the JSON was not valid you would get a different exception. I've got not clue what the problem is then. Is that piece of code being use by multiple threads? I can't think of anything else.

Tiago Fernandez Over a year ago

There's nothing special about this code, I'm reproducing the issue with a simple NUnit test case. Now I'm using Xamarin Studio 4.0, I wonder if Mono's implementation is buggy or whatever.

MeTitus Over a year ago

Ok that says it all, yes I would say that mono has an implementation problem, I thought you were using .Net (windows)

Tiago Fernandez · Accepted Answer · 2013-05-10 16:43:15Z

1

Since I could not make Dictionary<string, object> work, I've decided to drop it and use static types instead. BTW, this online tool is quite handy for generating C# classes from JSON.

answered May 10, 2013 at 16:43

Tiago Fernandez

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