What ": this" means in C#?

Question

I am looking on some code and I see:

public class AccountController : Controller
{
   public AccountController()   
          : this(new xxxxxx...

I understand it is a constructor of AccountController, but was is the meaning of ": this"?

Thanks, zalek

score 1 · Answer 1 · answered Mar 01 '15 at 15:00

:this after a constructor will invoke another overload of the constructor.

Consider this:

public class Offer {
    public string offerTitle { get; set; }
    public string offerDescription { get; set; }
    public string offerLocation { get; set; }

    public Offer():this("title") {

    }

    public Offer(string offerTitle) {
        this.offerTitle = offerTitle;
    }
}

If the caller invokes new Offer(), then, internally it will invoke another constructor which will set the offerTitle to "title".

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

0

It makes sure an overloaded constructor in the same class is called, e.g.:

class MyClass
{
    public MyClass(object obj) : this()
    {
        Console.WriteLine("world");
    }

    public MyClass()
    {
        Console.WriteLine("Hello");
    }
}

Output when calling the constructor with an argument:

Hello

world

edited Jun 20 '20 at 09:12

Community

1
1

answered Mar 01 '15 at 15:01

Emile Pels

3,837
1
15
23

Actually output will be "Helloworld" – JustSomeGuy Mar 01 '15 at 15:01
`Console.WriteLine` appends a line terminator, so no - it will not. – Emile Pels Mar 01 '15 at 15:03
Oops, even "Hello world" then. Nevermind – JustSomeGuy Mar 01 '15 at 15:03

score 0 · Answer 3 · answered Mar 01 '15 at 15:02

0

:this means that it will call parent's main class constructor (in this case Controller)

answered Mar 01 '15 at 15:02

Pedro Duque

15
3

This answer is wrong. – ataravati Mar 01 '15 at 15:21

ataravati · Answer 4 · 2015-03-01T15:25:15.363

The this keyword allows you to call one constructor from another constructor in the same class. Let's say you have two constructors in your class, one with parameters and one without parameters. You can use the this keyword on the constructor with no parameter to pass default values to the constructor with parameters, like this:

public class AccountController : Controller
{
   public AccountController() : this(0, "")   
   {
       // some code
   }

   public AccountController(int x, string y)   
   {
       // some code
   }
}

There's also a base keyword that you can use to call a constructor in the base class. The constructor in the following code will call the constructor of the Controller class.

public class AccountController : Controller
{
   public AccountController() : base()   
   {
       // some code
   }
}

What ": this" means in C#?

4 Answers4