Storing Lists Inside An Array

Question

Is it possible to store a Class that contains a List inside an array?

I am having some trouble with this concept.

Here's my code:

My Class Called "arrayItems":

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EngineTest
{
    [Serializable] //List olarak save etmemiz için bu gerekli.
    public class arrayItems
    {
        public List<items> items = new List<items>();
    }
}

Here's the definition of my Array called "tileItems":

 public static arrayItems[, ,] tileItems;

Here's how I create my Array:

    Program.tileItems = new arrayItems[Program.newMapWidth, Program.newMapHeight, Program.newMapLayers];

The problem I am facing is that the content of my Array is null. And I am getting this error:

Object reference not set to an instance of an object.

When I try to populate the List inside the array by Add() command I get the same error.

Can you direct me to the right direction please? Thanks in advance.

Answer 1

You need to initialise each list within the array:

for (int i = 0; i < newMapWidth; i++)
{
    for (int j = 0; j < newMapHeight; j++)
    {
        for (int k = 0; k < newMapLayers; k++)
        {
            arrayItems[i,j,k] = new arrayItems();
        }
    }
}

first.

Answer 2

You are creating and array of arrayItems , which is a reference type, because you defined it as a class. So when you initialize your array, all elements will be assigned null by default. That's why you get the error. You have to initialize each element of your array.

Answer 3

Since you are already initializing the list within the class definition you do not need to re-initialize the list property of arrayItems within the loop.

You have an array that has a bunch of pointers that point to nothing. So you actually need to instiante a new arrayItems in each array element first.

for (int i = 0; i < newMapWidth; i++)
{
    for (int j = 0; j < newMapHeight; j++)
    {
        for (int k = 0; k < newMapLayers; k++)
        {
            arrayItems[i,j,k]= new arrayitem();
        }
    }
}