Cant Figure out this c# reference

Question

I was using the "this" keyword in my default constructor, below is the code in the class movie

namespace Movie_List
{ enum GenreType { Action, War, Drama, Thriller }; 
 class Movie 
 { 
    //Data Members 
    private String _title; 
    private int _rating; 
    private GenreType _type;

    //Properties


    public GenreType GenType
    {
        get { return _type; }
        set { _type = value; }
    }
    public String Title
    {
        get { return _title; }
        set { _title = value; }
    }


    public int Rating
    {
        get { return _rating; }
        set { _rating = value; }
    }




    public Movie()
        : this("Jaws", GenreType.Action, 4) { } 

    public Movie(String title, GenreType type, int rating ) //working ctor
    {
        Title = title;
        GenType = type;
        Rating = rating;

    }

    public override string ToString()
    {           
        return String.Format(" {0} Genre : {1},  Rating: {2:d} Stars. ", Title, GenType, Rating);
    }

}

I wanted to read in from a text file so i used this code in the MainWindow.xaml.cs

private void btnLoad_Click(object sender, RoutedEventArgs e)
{

    string lineIn = "";
    string[] filmarray;
    using (StreamReader file = new StreamReader("filmlist.txt"))
    {
        while ((lineIn = file.ReadLine()) != null)
        {
            filmarray = lineIn.Split(new char[] { ',' });
            moviecollection.Add(new Movie()

            {
                Title = filmarray[0],
                GenType = (GenreType)Enum.Parse(typeof(GenreType), filmarray[1]),
                Rating = Convert.ToInt32(filmarray[2]),
            });
            lstFilms.ItemsSource = moviecollection;
        }


    }
}

I dont need this bit of code now

: this("Jaws", GenreType.Action, 4)

But when i deleted it, the genre action and rating 0 stars still prints.

Why is this Happening does anyone know?

Answer 1

When you have this initialization:

Movie movie = new Movie();

the empty constructor

public Movie() : this("Jaws", GenreType.Action, 4) { } 

calls the overloaded constructor which have several parameters:

public Movie(String title, GenreType type, int rating) { ... }

When you delete this line: this("Jaws", GenreType.Action, 4) { } , what is happening now is that you are only calling the empty constructor which does nothing at all.

So when you call

int ratingValue = movie.Rating;

the default value of integer which is zero is returned because you did set anything on it.

UPDATE

a simple if ( maybe, if I understand what you mean )

Assuming Rating should be greater than zero.

public override string ToString()
{     
    if (Rating == 0)
    {
        return String.Format("{0}", Title);
    }
    else
    {
        return String.Format(" {0} Genre : {1},  Rating: {2:d} Stars. ", Title, GenType, Rating);
    }
}

Answer 2

It's because enum and int are always initialized with default value of 0.

It's not like string - if you don't initialize it will equal null . If you want to emulate this behavior for int , you can always try using int? type.

To get more details on this subject take a look at Default Values Table (C#) .