C# this

Summary: in this tutorial, you’ll learn about C# this keyword and how to use it effectively.

What is this keyword in C#

A class is a blueprint for creating objects. To reference the current object inside the class, you use the this keyword. Therefore, the this keyword refers to the current instance of the class.

To explicitly reference a field inside a method of a class, you use the this keyword, followed by the dot operator (.), and the field name like this:

this.FieldNameCode language: C# (cs)

Likewise, you can use the this keyword to explicitly call a method in another method of the class:

this.MethodName(arguments)Code language: C# (cs)

C# this keyword example

The following example defines the Person class with the fields FirstName and LastName and two methods GetFullName() and SayHi():

// Person.cs

class Person
{
    public string FirstName;
    public string LastName;

    public string GetFullName()
    {
        return $"{this.FirstName} {this.LastName}";
    }
    public string SayHi()
    {
        return $"Hi, I'm {this.GetFullName()}.";
    }
}Code language: C# (cs)

In this example, we use the this keyword to reference the FirstName and LastName fields in the GetFullName() method. Also, we use the this keyword to call the GetFullName() method in the SayHi() method.

The following creates a new instance of the Person class and call the SayHi() method:

// Program.cs

// Create a new instance of the Person class
Person p1 = new();
p1.FirstName = "John";
p1.LastName = "Doe";

// Show the fullname
Console.WriteLine(p1.GetFullName());

// Display the greeting
Console.WriteLine(p1.SayHi());Code language: C# (cs)

When calling the p1.GetFullName() method, the this keyword references the p1 object. So the FirstName and LastName fields are "John" and "Doe" respectively.

The SayHi() method calls the GetFullName() method via the this keyword. Therefore, the p1.GetFullName() method returns the "John Doe" string. Hence, the SayHi() method returns the string "Hi, I'm John Doe.".

Using C# this keyword for method chaining

The following example adds two new methods SetFirstName() and SetLastName() to the Person class:

// Person.cs

class Person
{
    public string FirstName;
    public string LastName;

    public string GetFullName()
    {
        return $"{this.FirstName} {this.LastName}";
    }

    public string SayHi()
    {
        return $"Hi, I'm {this.GetFullName()}.";
    }

    public Person SetFirstName(string firstName)
    {
        this.FirstName = firstName;
        return this;
    }

    public Person SetLastName(string lastName)
    {
        this.LastName = lastName;
        return this;

    }
}Code language: C# (cs)

In this example, the SetFirstName() and SetLastName() methods assign their arguments to the FirstName and LastName fields and return the current instance of the Person class.

The following creates a new Person object, calls the SetFirstName(), SetLastName(), and SayHi() methods:

// Program.cs

Person p1 = new();

p1.SetFirstName("John");
p1.SetLastName("Doe");
string greeting = p1.SayHi();

Console.WriteLine(greeting);Code language: C# (cs)

Since both SetFirstName() and SetLastName() methods return the current Person‘s object, you can replace three statements with one statement as follows:

// Program.cs


Person p1 = new();

string greeting = p1.SetFirstName("John")
                    .SetLastName("Doe")
                    .SayHi();

Console.WriteLine(greeting);Code language: C# (cs)

This technique is called method chaining.

How it works.

The SetFirstName() method returns this that is the p1 object:

p1.SetFirstName("John");Code language: C# (cs)

However, you don’t need to use an immediate variable to store the p1. And you can immediately call SetLastName() of the p1 object like this:

p1.SetFirstName("John")
  .SetLastName("Doe");Code language: C# (cs)

Since the SetLastName() method also returns this that is the p1 object, you can call the SayHi() method on it immediately. Because the SayHi() method returns a string, you can assign it to the greeting variable:

// Program.cs

Person p1 = new();

string greeting = p1.SetFirstName("John")
                    .SetLastName("Doe")
                    .SayHi();

Console.WriteLine(greeting);Code language: C# (cs)

Summary

• The C# this keyword refers to the current object of the class.
• Use C# this keyword for method chaining to make the code more concise.