Add property to ExpandoObject with the same name as a string

Question

Is there a way to add a property to an ExpandoObject with the same name as a string value?

For example, if I have:

string propName = "ProductNumber";
dynamic obj = new System.Dynamic.ExpandoObject();

I can create the property ProductNumber like:

obj.ProductNumber = 123;

But, can I create the property obj.ProductNumber based on the string propName? So, if I don't know what the name of the property will be in advanced, I can create it based on this input. If this is not possible with ExpandoObject, any other areas of C# I should look into?

possible duplicate of Adding unknown (at design time) properties to an ExpandoObject — stijn
– stijn, Commented Jun 11, 2013 at 17:08
Practical use of the above found here: stackoverflow.com/questions/2974008/… — Nic
– Nic, Commented Aug 5, 2014 at 14:41

phoog · Accepted Answer · 2012-04-06 20:02:11Z

44

ExpandoObject implements IDictionary<string, object>:

((IDictionary<string, object>)obj)[propName] = propValue

I don't know off the top of my head whether you can use the indexer syntax with a dynamic reference (i.e., without the cast), but you can certainly try it and find out.

edited Apr 6, 2012 at 20:02

answered Apr 6, 2012 at 19:45

phoog

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5 Comments

Mike Corcoran Over a year ago

you can't index an ExpandoObject as you've done in your first example

Paul Over a year ago

Second example is good. First example gives Cannot apply indexing with [] to an expression of type 'System.Dynamic.ExpandoObject'

phoog Over a year ago

@Paul thanks -- I had forgotten that the indexer is an explicit interface implementation. Answer edited.

phoog Over a year ago

@VBRonPaulFan yes, I had forgotten that the interface implementation is explicit. I've edited the answer.

Tony Over a year ago

man, i am so glad i found this post. i was about to implement some object off of DynamicObject from some other tutorials just to get this ability. life and time saver thanks!! :D

BrokenGlass · Accepted Answer · 2012-04-06 19:46:41Z

21

Cast the ExpandoObject to an IDictionary<string,object> to do this:

string propName = "ProductNumber";
dynamic obj = new System.Dynamic.ExpandoObject();
var dict = (IDictionary<string,object>)obj;
dict[propName] = 123;

answered Apr 6, 2012 at 19:46

BrokenGlass

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1 Comment

Jim Schubert Over a year ago

+1 for at least mentioning that ExpandoObject is IDictionary<string,object> underneath. See docs

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