C# Is Type in list question

Question

Basic c# question. In the sample bellow But the 'is' doesn't like the type variable. Any ideas there should be a simple answer.

    List<object> list = new List<object>();
    list.Add("one");
    list.Add(2);
    list.Add('3');

    Type desiredType = typeof(System.Int32);

    if (list.Any(w => w is desiredType))
    {
        //do something
    }

Putting heterogeneous data in a list is asking for trouble, btw... — Marc Gravell
– Marc Gravell, Commented Apr 27, 2011 at 12:01
That's a nasty way to use generics, but I guess it's for demonstration only. — vgru
– vgru, Commented Apr 27, 2011 at 12:03

as-cii · Accepted Answer · 2011-04-27 12:02:13Z

6

Try this:

List<object> list = new List<object>();
list.Add("one");
list.Add(2);
list.Add('3');

Type desiredType = typeof(System.Int32);

if (list.Any(w => w.GetType().IsAssignableFrom(desiredType)))
{
    //do something
}

Anyway: are you sure you want to create a list of objects?

answered Apr 27, 2011 at 12:02

as-cii

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Comments

Femaref · Accepted Answer · 2011-04-27 11:58:56Z

4

w.GetType() == desiredType.

Why are you abusing generics like that?

answered Apr 27, 2011 at 11:58

Femaref

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3 Comments

Marc Gravell Over a year ago

Note that type equality isn't quite the same as is; subclasses etc will be confusing...

Ryan Mrachek Over a year ago

Thank you.. IRL our app has a dozen panel types in a collection and wanted a generic way to determine if a panel of a particular type is already open.

vgru Over a year ago

Actually, AS-CII's answer should be closer to is behavior.

Todd Stout · Accepted Answer · 2011-04-27 12:12:22Z

3

You could use the Linq extension method OfType:

list.OfType<> will return an IEnumerable to any items of the specified type.

edited Apr 27, 2011 at 12:12

answered Apr 27, 2011 at 12:07

Todd Stout

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1 Comment

Mania Over a year ago

This is what you want 9 times out of 10. The other 1/10 time the type isn't known at compile time (ie it's passed as a parameter rather than type parameter of a generic method), in which case you should use AS-CII's method. But usually OfType is what you want. Additionally OfType saves you the cast when you want to retrieve the values, which is handy.

Morten Jacobsen · Accepted Answer · 2011-04-27 11:59:39Z

1

If I recall correctly you have to write w is System.Int32..

answered Apr 27, 2011 at 11:59

Morten Jacobsen

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Comments

matt · Accepted Answer · 2011-04-27 12:00:08Z

1

The delegate is expecting a type or a namespace, but you're supplying a type instance. Try this:

if (list.Any(w => w is Int32))
{
    //do something
}

answered Apr 27, 2011 at 12:00

matt

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1 Comment

matt Over a year ago

How was that "the point"? Your initial question stated that 'is doesn't like the type variable', and that there should be a simple answer. Saying w is Int32 is a lot simpler than getting a type instance and writing if (list.Any(w => w.GetType().IsAssignableFrom(desiredType)))

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