How to detect if a property exists on an ExpandoOb

Question

In javascript you can detect if a property is defined by using the undefined keyword:

if( typeof data.myProperty == "undefined" ) ...

How would you do this in C# using the dynamic keyword with an ExpandoObject and without throwing an exception?

Answer 1

I wanted to create an extension method so I could do something like:

dynamic myDynamicObject;
myDynamicObject.propertyName = "value";

if (myDynamicObject.HasProperty("propertyName"))
{
    //...
}

... but you can't create extensions on ExpandoObject according to the C# 5 documentation (more info here).

So I ended up creating a class helper:

public static class ExpandoObjectHelper
{
    public static bool HasProperty(ExpandoObject obj, string propertyName)
    {
        return ((IDictionary<String, object>)obj).ContainsKey(propertyName);
    }
}

To use it:

// If the 'MyProperty' property exists...
if (ExpandoObjectHelper.HasProperty(obj, "MyProperty"))
{
    ...
}

Answer 2

Try this one

public bool PropertyExist(object obj, string propertyName)
{
 return obj.GetType().GetProperty(propertyName) != null;
}

Answer 3

This extension method checks for the existence of a property and then returns the value or null. This is useful if you do not want your applications to throw unnecessary exceptions, at least ones you can help.

    public static object Value(this ExpandoObject expando, string name)
    {
        var expandoDic = (IDictionary<string, object>)expando;
        return expandoDic.ContainsKey(name) ? expandoDic[name] : null;
    }

If can be used as such :

  // lookup is type 'ExpandoObject'
  object value = lookup.Value("MyProperty");

or if your local variable is 'dynamic' you will have to cast it to ExpandoObject first.

  // lookup is type 'dynamic'
  object value = ((ExpandoObject)lookup).Value("PropertyBeingTested");

Answer 4

(authorDynamic as ExpandoObject).Any(pair => pair.Key == "YourProp");