Cast received object to a List<object> or IEnumerable<object>

user_75846 0
Viewed 258709

I'm trying to perform the following cast 

private void MyMethod(object myObject)  
{  
    if(myObject is IEnumerable)  
    {
        List<object> collection = (List<object>)myObject;  
        ... do something   
    }  
    else  
    {  
        ... do something  
    }  
}

But I always end up with the following excepction:

Unable to cast object of type 'System.Collections.Generic.List1[MySpecificType]' to type 'System.Collections.Generic.List1[System.Object]'

I really need this to work because this method needs to be very generic to receive single objects and collections both of unspecified types.

Is this possible, or is there another way of accomplishing this.

Thank you.

.net c#
10 Answers

C# 4 will have covariant and contravariant template parameters, but until then you have to do something nongeneric like

IList collection = (IList)myObject;
user_471610

You can't cast an IEnumerable<T> to a List<T>.

But you can accomplish this using LINQ:

var result = ((IEnumerable)myObject).Cast<object>().ToList();
user_642620

Problem is, you're trying to upcast to a richer object. You simply need to add the items to a new list: 

if (myObject is IEnumerable)
{
   List<object> list = new List<object>();
   var enumerator = ((IEnumerable) myObject).GetEnumerator();
   while (enumerator.MoveNext())
   {
      list.Add(enumerator.Current);
   }
}
user_621860

Do you actually need more information than plain IEnumerable gives you? Just cast it to that and use foreach with it. I face exactly the same situation in some bits of Protocol Buffers, and I've found that casting to IEnumerable (or IList to access it like a list) works very well.

user_226560

How about

List<object> collection = new List<object>((IEnumerable)myObject);
Cameron_MacFarland_38200

Nowadays it's like:

var collection = new List<object>(objectVar);
user_47459820

You could also convert object to a list of your DTO.

First serialize myObject and then deserilize it into your List.

Here is the code:

List<MyDto> myList = JsonConvert.DeserializeObject<List<MyDto>>(JsonConvert.SerializeObject(myObject));

The Newtonsoft.Json is used in the above code.

user_78267740
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