Declaring an Array from a Class in C#

Question

I want to create an Array of "Highscore" objects that I defined with a class.
I'm always getting a NullReferenceException when I try to set or read the Value of a specific Array content.

It does work when I use a single Highscore object instead of an Array.

It also does work when I use an integer array instead of an Highscore Array.

Code

class Highscore
{
    public int score;
}
class Program
{
    static void Main()
    {
        Highscore[] highscoresArray = new Highscore[10];
        highscoresArray[0].score = 12;
        Console.WriteLine(highscoresArray[0].score);
        Console.ReadLine();
    }
}

System.NullReferenceException:

highscoresArray[] was null.

Highscore[] highscoresArray = Enumerable.Range(0, 10).Select(x => new Highscore()).ToArray(); — Dmitrii Bychenko
– Dmitrii Bychenko, Commented Nov 6, 2019 at 11:16

Dmitrii Bychenko · Accepted Answer · 2019-11-06 11:16:46Z

7

in this code:

Highscore[] highscoresArray = new Highscore[10];

you instantiate an array of Highscore objects but you do not instantiate each object in the array.

you need to then do

for(int i = 0; i < highscoresArray.Length; i++)
    highscoresArray[i]  = new Highscore();

edited Nov 6, 2019 at 11:16

Dmitrii Bychenko

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answered Nov 6, 2019 at 11:08

Tim Rutter

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Comments

Marce · Accepted Answer · 2019-11-06 11:08:42Z

1

You have to add a Highscore to the array first, for example:

highscoresArray[0] = new Highscore();

answered Nov 6, 2019 at 11:08

Marce

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Comments

Aly Elhaddad · Accepted Answer · 2019-11-06 11:09:13Z

1

That's because you've created an array, set its length, but never actually instantiated any of its elements. One way to do so would be:

Highscore[] highscoresArray = new Highscore[10];
highscoresArray[0] = new Highscore();

answered Nov 6, 2019 at 11:09

Aly Elhaddad

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Comments

CR0N0S.LXIII · Accepted Answer · 2019-11-06 11:08:36Z

0

Maybe you need to initialize every item of the array:

 for (int i = 0; i < highscoresArray.length; i++)
 {
      highscoresArray[i] = new Highscore();
 }

answered Nov 6, 2019 at 11:08

CR0N0S.LXIII

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Comments

Dmitriy Gavrilenko · Accepted Answer · 2019-11-06 12:32:20Z

0

.. Or use a Struct

struct Highscore
{
    public int score;
}

answered Nov 6, 2019 at 12:32

Dmitriy Gavrilenko

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3 Comments

Joshua Drake Over a year ago

What are the dis/advantages of a struct?

Dmitriy Gavrilenko Over a year ago

@JoshuaDrake Specifically in this case - no initialization required.

Joshua Drake Over a year ago

The comment came from the review queue, we prefer answers to include the why, and not just the code.

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