Dynamically adding properties to an ExpandoObject

Question

I would like to dynamically add properties to a ExpandoObject at runtime. So for example to add a string property call NewProp I would like to write something like

var x = new ExpandoObject();
x.AddProperty("NewProp", System.String);

Is this easily possible?

possible duplicate of [How to set a property of a C# 4 dynamic object when you have the name in another variable](http://stackoverflow.com/questions/3033410/how-to-set-a-property-of-a-c-sharp-4-dynamic-object-when-you-have-the-name-in-an) — nawfal, Jul 19 '14 at 15:55

score 577 · Accepted Answer · answered Feb 08 '11 at 21:05

577

dynamic x = new ExpandoObject();
x.NewProp = string.Empty;

Alternatively:

var x = new ExpandoObject() as IDictionary<string, Object>;
x.Add("NewProp", string.Empty);

answered Feb 08 '11 at 21:05

Stephen Cleary

406,130
70
637
767

38

I've never realized that Expando *implements* IDictionary. I've always thought that cast would copy it to a dictionary. However, your post made me understand that if you change the Dictionary, you also change the underlying ExpandoObject! Thanks a lot – Dynalon Jan 27 '12 at 18:48
It is amazing, and I have demonstrate that they are actually becoming properties of the object with sample code in my post on http://stackoverflow.com/questions/11888144/name-variable-using-string-net/11893463#11893463, thanks – yoel halb Aug 10 '12 at 02:42
3

getting `Error 53 Cannot convert type 'System.Dynamic.ExpandoObject' to 'System.Collections.Generic.IDictionary' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion` – TheVillageIdiot Oct 30 '12 at 09:23
27

It's `IDictionary`, not `IDictionary`. – Stephen Cleary Oct 30 '12 at 13:29
It might not be a good idea to cast to dictionary and add properties. https://connect.microsoft.com/VisualStudio/feedback/details/783541/expandoobjects-leak-memory-when-used-as-an-idictionary-string-object-to-add-new-properties – Marko Jan 16 '15 at 10:52
@Marko: That "leak" is only if you add many different property names, and would have the same exact behavior if you added the same property names via `dynamic`. – Stephen Cleary Jan 16 '15 at 14:27
May worth pointing out the first one doesn't work with `var x`. It only works with `dynamic x`. – Adam Szabo Sep 14 '15 at 10:44
That's beautiful, exactly what I wanted. – garryp Aug 17 '16 at 14:49
Kudos for providing 2 implementations – Leo Gurdian Mar 23 '17 at 00:13
11

It's important to note that when you're casting as `IDictionary` that you don't use `dynamic` as the variable type. – user3791372 May 14 '17 at 17:42
1

If you implement as an IDictionary, then you don't have to cast it to use the methods from either the parent or derived class: `IDictionary myExpando = new ExpandoObject();` – Abel Wenning Mar 11 '21 at 00:14

score 28 · Answer 2 · edited May 03 '22 at 20:55

28

As explained here by Filip - http://www.filipekberg.se/2011/10/02/adding-properties-and-methods-to-an-expandoobject-dynamicly/

You can add a method too at runtime.

var x = new ExpandoObject() as IDictionary<string, Object>;
x.Add("Shout", new Action(() => { Console.WriteLine("Hellooo!!!"); }));
x.Shout();

edited May 03 '22 at 20:55

Chris Marisic

31,683
22
160
255

answered Oct 15 '15 at 19:37

Himanshu Patel

646
7
12

1

Your code is plain wrong, you skipped the most important part, which is the cast to a Dictionary. – tocqueville Nov 18 '20 at 15:17

score 21 · Answer 3 · edited Oct 04 '21 at 07:14

Here is a sample helper class which converts an Object and returns an Expando with all public properties of the given object.

public static class dynamicHelper
    {
        public static ExpandoObject convertToExpando(object obj)
        {
            //Get Properties Using Reflections
            BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;
            PropertyInfo[] properties = obj.GetType().GetProperties(flags);

            //Add Them to a new Expando
            ExpandoObject expando = new ExpandoObject();
            foreach (PropertyInfo property in properties)
            {
                AddProperty(expando, property.Name, property.GetValue(obj));
            }

            return expando;
        }

        public static void AddProperty(ExpandoObject expando, string propertyName, object propertyValue)
        {
            //Take use of the IDictionary implementation
            var expandoDict = expando as IDictionary<String, object>;
            if (expandoDict.ContainsKey(propertyName))
                expandoDict[propertyName] = propertyValue;
            else
                expandoDict.Add(propertyName, propertyValue);
        }
    }

Usage:

//Create Dynamic Object
dynamic expandoObj= dynamicHelper.convertToExpando(myObject);
    
//Add Custom Properties
dynamicHelper.AddProperty(expandoObj, "dynamicKey", "Some Value");

"var expandoDict = expando as IDictionary;" this line need to change to "var expandoDict = expando as IDictionary;" — Jom George, Jun 02 '17 at 09:43
To make it even more awesome use those as extension methods. — Rogerio Schmitt, Apr 14 '21 at 17:30

Morteza ebrahim nejad · Answer 4 · 2020-03-30T14:33:05.583

0

i think this add new property in desired type without having to set a primitive value, like when property defined in class definition

var x = new ExpandoObject();
x.NewProp = default(string)

edited Mar 30 '20 at 14:33

answered Mar 30 '20 at 00:15

Morteza ebrahim nejad

11
2

7

Hey Morteza ! Code-only answers may solve the problem but they are much more useful if you explain how they solve it. Community requires theory as well as code both to understand your answer fully. – RBT Mar 30 '20 at 00:57

Dynamically adding properties to an ExpandoObject

4 Answers4

Linked

Related