How to use the “is” operator in System.Type variables?

Question

here is what a I'm doing:

object ReturnMatch(System.Type type)  
{  
    foreach(object obj in myObjects)  
    {
        if (obj == type)  
        {  
            return obj;  
        }  
    }  
}  

However, if obj is a subclass of type , it will not match. But I would like the function to return the same way as if I was using the operator is .

I tried the following, but it won't compile:

if (obj is type) // won't compile in C# 2.0  

The best solution I came up with was:

if (obj.GetType().Equals(type) || obj.GetType().IsSubclassOf(type))  

Isn't there a way to use operator is to make the code cleaner?

Answer 1

I've used the IsAssignableFrom method when faced with this problem.

Type theTypeWeWant; // From argument or whatever
foreach (object o in myCollection)
{
    if (theTypeWeWant.IsAssignableFrom(o.GetType))
         return o;
}

Another approach that may or may not work with your problem is to use a generic method:

private T FindObjectOfType<T>() where T: class
{
    foreach(object o in myCollection)
    {
        if (o is T)
             return (T) o;
    }
    return null;
}

(Code written from memory and is not tested)

Answer 2

也许

type.IsAssignableFrom(obj.GetType())

Answer 3

Not using the is operator, but the Type.IsInstanceOfType Method appears to be what you're looking for.

http://msdn.microsoft.com/en-us/library/system.type.isinstanceoftype.aspx

Answer 4

the is operator indicates whether or not it would be 'safe' to cast one object as another obeject (often a super class).

if(obj is type)

if obj is of type 'type' or a subclass thereof, then the if statement will succeede as it is 'safe' to cast obj as (type)obj.

see: http://msdn.microsoft.com/en-us/library/scekt9xw(VS.71).aspx

Answer 5

Is there a reason why you cannot use the "is" keyword itself?

foreach(object obj in myObjects)
{
  if (obj is type)
  {
    return obj;
  }
}

EDIT - I see what I was missing. Isak's suggestion is the correct one; I have tested and confirmed it.

  class Level1
  {
  }

  class Level2A : Level1
  {
  }

  class Level2B : Level1
  {
  }

  class Level3A2A : Level2A
  {
  }


  class Program
  {
    static void Main(string[] args)
    {
      object[] objects = new object[] {"testing", new Level1(), new Level2A(), new Level2B(), new Level3A2A(), new object() };


      ReturnMatch(typeof(Level1), objects);
      Console.ReadLine();
    }


    static void ReturnMatch(Type arbitraryType, object[] objects)
    {
      foreach (object obj in objects)
      {
        Type objType = obj.GetType();

        Console.Write(arbitraryType.ToString() + " is ");

        if (!arbitraryType.IsAssignableFrom(objType))
          Console.Write("not ");

        Console.WriteLine("assignable from " + objType.ToString());

      }
    }
  }