CODEWITHSUNDEEP
c#.netienumerable
Max Toro
Max Toro

Reputation: 28608

Best way to test if a Type is a collection

I have a method that accepts a parameter obj of type System.Object

Now I want to check if the actual type of obj is:

The first way I thought of is:

if (obj is IEnumerable) 
   // obj is a collection

But System.String implements IEnumerable, and I don't want to treat string as a collection.

The second way I thought is testing for ICollection instead of IEnumerable, since IEnumerable is more of a potential collection than an actual one. This would leave out string, but also ICollection-Of-T because it does not inherit ICollection (IEnumerable-Of-T is the only generic collection abstraction that's backwards compatible - it inherits IEnumerable).

So I guess the best way is:

if (obj is string) 
  // not a collection
else if (obj is IEnumerable) 
  // collection
else
  // not a collection

Is there a better way?

Upvotes: 7

Views: 6371

Answers (3)

Pavel Minaev
Pavel Minaev

Reputation: 101555

If you really only want to test:

bool isCollection = obj.GetType().GetInterfaces()
    .Any(iface => iface.IsGenericType && iface.GetGenericTypeDefinition() == typeof(ICollection<>))

But frankly, if you really only want to special-case string (why, by the way?), then just do so. If you test for ICollection<>, you will treat the result of a LINQ query as "non-collection", for example, for no good reason.

Upvotes: 5

Elvis Skensberg
Elvis Skensberg

Reputation: 149

If you want to do a check and get true for tpyes (includes nullables) any list/collection/IEnumerable, but get false for type of string, then

   private static bool IsIEnumerable(Type requestType)
   {
      var isIEnumerable = typeof(IEnumerable).IsAssignableFrom(requestType);
      var notString = !typeof(string).IsAssignableFrom(requestType);
      return isIEnumerable && notString;
   }

Upvotes: -1

JaredPar
JaredPar

Reputation: 754505

I think you're over complicating this a bit. If you really want to use IEnumerable but exclude System.String, why not just do that directly in code? 

public static bool IsCollection(object obj) {
  return obj is IEnumerable && !(obj is String);
}

Upvotes: 10

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