How can I deserialize JSON to a simple Dictionary<string,string> in ASP.NET?

Json.NET does this...

string json = @"{""key1"":""value1"",""key2"":""value2""}";

var values = JsonConvert.DeserializeObject<Dictionary<string, string>>(json);

More examples: Serializing Collections with Json.NET

I did discover .NET has a built in way to cast the JSON string into a Dictionary<String, Object> via the System.Web.Script.Serialization.JavaScriptSerializer type in the 3.5 System.Web.Extensions assembly. Use the method DeserializeObject(String).

I stumbled upon this when doing an ajax post (via jquery) of content type 'application/json' to a static .net Page Method and saw that the method (which had a single parameter of type Object) magically received this Dictionary.

System.Text.Json

This can now be done using System.Text.Json which is built-in to .NET Core 3.0. It's now possible to deserialize JSON without using third-party libraries.

var json = @"{""key1"":""value1"",""key2"":""value2""}";
var values = JsonSerializer.Deserialize<Dictionary<string, string>>(json);

Also available in NuGet package System.Text.Json if using .NET Standard or .NET Framework.

Make sure to read and understand:

• https://github.com/dotnet/runtime/issues/30452

Edit: This works, but the accepted answer using Json.NET is much more straightforward. Leaving this one in case someone needs BCL-only code.

It’s not supported by the .NET framework out of the box. A glaring oversight – not everyone needs to deserialize into objects with named properties. So I ended up rolling my own:

VB.NET:

<Serializable()> Public Class StringStringDictionary
    Implements ISerializable
    Public dict As System.Collections.Generic.Dictionary(Of String, String)
    Public Sub New()
        dict = New System.Collections.Generic.Dictionary(Of String, String)
    End Sub
    Protected Sub New(info As SerializationInfo, _
          context As StreamingContext)
        dict = New System.Collections.Generic.Dictionary(Of String, String)
        For Each entry As SerializationEntry In info
            dict.Add(entry.Name, DirectCast(entry.Value, String))
        Next
    End Sub
    Public Sub GetObjectData(info As SerializationInfo, context As StreamingContext) Implements ISerializable.GetObjectData
        For Each key As String in dict.Keys
            info.AddValue(key, dict.Item(key))
        Next
    End Sub
End Class

same on C#:

public class StringStringDictionary : ISerializable
{
    public System.Collections.Generic.Dictionary<string, string> dict;
    public StringStringDictionary()
    {
        dict = new System.Collections.Generic.Dictionary<string, string>();
    }
    protected StringStringDictionary(SerializationInfo info, StreamingContext context)
    {
        dict = new System.Collections.Generic.Dictionary<string, string>();
        foreach (SerializationEntry entry in info)
            dict.Add(entry.Name, (string)entry.Value);
    }
    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        foreach (string key in dict.Keys)
            info.AddValue(key, dict[key]);
    }
}

Called with:

string MyJsonString = "{ \"key1\": \"value1\", \"key2\": \"value2\"}";
System.Runtime.Serialization.Json.DataContractJsonSerializer dcjs = new
  System.Runtime.Serialization.Json.DataContractJsonSerializer(
    typeof(StringStringDictionary));
System.IO.MemoryStream ms = new
  System.IO.MemoryStream(Encoding.UTF8.GetBytes(MyJsonString));
StringStringDictionary myfields = (StringStringDictionary)dcjs.ReadObject(ms);
Response.Write("Value of key2: " + myfields.dict["key2"]);

Sorry for the mix of C# and VB.NET…

For anyone who is trying to convert JSON to dictionary just for retrieving some value out of it. There is a simple way using Newtonsoft.JSON

using Newtonsoft.Json.Linq
...

JObject o = JObject.Parse(@"{
  'CPU': 'Intel',
  'Drives': [
    'DVD read/writer',
    '500 gigabyte hard drive'
  ]
}");

string cpu = (string)o["CPU"];
// Intel

string firstDrive = (string)o["Drives"][0];
// DVD read/writer

IList<string> allDrives = o["Drives"].Select(t => (string)t).ToList();
// DVD read/writer
// 500 gigabyte hard drive

Here is my solution with System.Text.Json. You get a json string for the nested objects which in own turn can be converted to needed type later on.

public static Dictionary<string,string> JsonToDictionary(this string json)
        {
            var objectValues = JsonSerializer.Deserialize<Dictionary<string, object>>(json);
            var stringValues = objectValues.Select(o => new KeyValuePair<string, string>(o.Key, o.Value?.ToString()));
            return stringValues.ToDictionary(pair => pair.Key, pair => pair.Value);
        }

Here is the usage example to fetch values from a nested object:

 var result= json.JsonToDictionary()["outerField"]
                .JsonToDictionary()["innerField"];

Note that this solution does not cover the json objects starting as an array like [12, 13]. These objects can be read as an array in the begining and then the extension method can be applied on each item, in case the items are complex objects with their own properties.