OfType

This C# method searches for elements by their types. The System.Linq namespace provides this generic method to test derived types.

By using this method, we get all the elements of a matching type. We do not need to cast the returned objects—we can use them directly.

To start, this example allocates an array of objects on the managed heap. It then assigns more derived types into each of the object reference elements.

using System;
using System.Linq;
using System.Text;

class Program
{
    static void Main()
    {
        // Create an object array.
        object[] array = new object[4];
        array[0] = new StringBuilder();
        array[1] = "example";
        array[2] = new int[1];
        array[3] = "another";

        // Filter the objects by their type.
        // ... Only match strings.
        // ... Print those strings to the screen.
        var result = array.OfType<string>();
        foreach (var element in result)
        {
            Console.WriteLine(element);
        }
    }
}
example
another

Inheritance

Consider this example: it has a base class Animal, and then derives 2 classes from it—Bird and Dog. We then use OfType to test the most derived types.

using System;
using System.Collections.Generic;
using System.Linq;

class Animal
{
}

class Bird : Animal
{
}

class Dog : Animal
{
    public int Color { get; set; }
}


class Program
{
    static void Main()
    {
        // Part 1: create List of Animal objects.
        var list = new List<Animal>();
        list.Add(new Dog() { Color = 20 });
        list.Add(new Bird());

        // Part 2: use OfType to get all Dogs in the list.
        foreach (Dog value in list.OfType<Dog>())
        {
            Console.WriteLine(value.Color);
        }
    }
}
20

A discussion

What is another way of using the OfType extension? One thing you can do is invoke OfType on the collection of Forms in a Windows Forms program.

A summary

The OfType extension is located in the System.Linq namespace in the C# language. It provides a useful way to query for elements of a certain type.