Question

The keyword this in C# is slightly different from other languages. I’ve been googling for a while, but I cannot find an article that will sum up all.

How can I use this in C#?

Answer 1

What is “this”? It is a keyword used in many object-oriented programming languages to refer to the current object. It can be implemented as a pointer (f.e. C++) or reference (f.e. Java), but in C# it has a few different meanings.

Classes

We can use “this” in 3 different contexts

• call other contructors
• refer to instance fields or methods
• pass current object

example:

public class Person
{
        private string name;

        public Person()
        {
            name = "John";
        }

        public Person(string name)
            : this() // call other constructor
        {
            // this is used to qualify the field
            // “name” is hidden by parameter
            this.name = name;
        }

        public string Name
        {
            get { return name; }
        }

        private void sayHi()
        {
            Console.WriteLine("Hi");
            Foo.SayName(this); //use this to pass current object 
        }

        public void Speak()
        {
            this.sayHi(); // use this to refer to an instance method
            Console.WriteLine("Want to come up and see my etchings? ");
        }
    }

class Foo 
{
    public static void SayName(Person person)
    {
        Console.WriteLine("My name is  {0}", person.Name);
    }
}

Indexers

Define an indexer for the type to have array-like semantics.

public int this[int index]
{
    get { return array[index]; }
    set { array[index] = value; }
}

Extension methods

class Foo 
{  
    // with “this” modifiler we can use it like instance method of Person
    public static void SayName(this Person person) 
    {
        Console.WriteLine(“My name is  {0}”, person.Name);
    }
}

Structures

struct MyVeryOwnInteger 
{
    private int x;
    public int Gimme() 
{
       // inside struct this is treated as a variable
       // not reference to current structure 
        return this.x; 
}