An array of classes where you pass the neighbors (Conways GoL)

Question

i tried to create the 'Conweys game of life'. So at first i create a empty (null) arrays of tile's. Then i set a list for each neightbour tile to commit it on the creating tile on this place of the array.

        private static Tile[,] GenerateGeneration(int rowlenght, int colLenght)
        {

            Tile[,] newGeneration = new Tile[rowlenght, colLenght]; //Emty array 

            for (int row = 0; row < rowlenght; row++)
            {
                for (int column = 0; column < colLenght; column++)
                {
                    List<Tile> tiles = new() //Set neighbourtiles in a list
                    {
                        newGeneration[row,CalculateIndexOverOrUnderflow(column - 1,colLenght)], //Left
                        newGeneration[CalculateIndexOverOrUnderflow(row - 1, rowlenght), CalculateIndexOverOrUnderflow(column - 1, colLenght)], //LeftAbove
                        newGeneration[CalculateIndexOverOrUnderflow(row - 1, rowlenght), column], //Above
                        newGeneration[CalculateIndexOverOrUnderflow((row - 1), rowlenght), CalculateIndexOverOrUnderflow((column + 1), colLenght)], //AboveRight
                        newGeneration[row, CalculateIndexOverOrUnderflow((column + 1), colLenght)], //Right
                        newGeneration[CalculateIndexOverOrUnderflow((row + 1), rowlenght), CalculateIndexOverOrUnderflow(column + 1, colLenght)], //BelowRight
                        newGeneration[CalculateIndexOverOrUnderflow((row + 1), rowlenght), column], //Below
                        newGeneration[CalculateIndexOverOrUnderflow((row + 1), rowlenght), CalculateIndexOverOrUnderflow(column - 1, colLenght)], //BelowLeft
                    };
                    

                    newGeneration[row, column] = new Tile(tiles, row, column); //commit the neighbours
                }
            }

            return newGeneration;
        }

The 'CalculateIndexOverOrUnderflow' methode sets the index to the upperbound of the array if it's < 0 and vice versa.

So my question is. On running this programm the most of the neighbours ar null. In my opinion all tiles should not be null, because a class is a reference type and I always pass the reference.

Answer 1

I always pass the reference

This's right, but null is also a reference in a sense, and all your tiles are null on initial. When you do this:

 List<Tile> tiles = new() //Set neighbourtiles in a list
 {
     newGeneration[row, column],
     ...
 }

If newGeneration[row, column] isn't set at that moment, the tile list will contain a null value.

The easiest solution is full fill the array with empty tiles first:

for (int row = 0; row < rowlenght; row++)
{
    for (int column = 0; column < colLenght; column++)
    {
        newGeneration[row, column] = new Tile(new Tiles(), row, column);
    }
}

Fill the tile list in each tile next:

for (int row = 0; row < rowlenght; row++)
{
    for (int column = 0; column < colLenght; column++)
    {
        var tiles = newGeneration[row, column].Tiles; // Assume the tile list is public
        tiles.Add(newGeneration[row,CalculateIndexOverOrUnderflow(column - 1,colLenght)]);
        tiles.Add(...);
    }
}