koobas.hobune.stream
Setting a property in a 2D array giving me an Object not set to Instance error.
I've created a class called Cell which has one property which is an int called Value. I'm trying to create a 2D array to create a grid of cells with random values, however whenever I try to set the value of Cell [x, y] I get this error;
NullReferenceException: Object reference not set to an instance of an object
I know this means that the object isn't getting created correctly, but I can't see why.
My Cell class
public class Cell : iCell {
int _value;
public int Value {
get {return _value;}
set {_value = value; }
}
public Cell ()
{
_value = 0;
}
}
My Grid Class
public class SudokuGrid : iSudokuGrid {
private Cell[,] _cells;
private Cell _currentCell;
private Cell _previousCell;
public Cell[,] Cells {
get { return _cells; }
set { _cells = value; }
}
public Cell CurrentCell {
get { return _currentCell;}
set { _currentCell = value;}
}
public Cell PreviousCell {
get { return _previousCell;}
set { _previousCell = value;}
}
public SudokuGrid() {
Cell [,] _cells = new Cell[9,9];
//int x = 0;
//int y = 0;
}
public void Generate() {
for (int x = 0; x < 9; x++) {
for (int y = 0; y < 9; y++) {
int rnd = Random.Range(1,9);
_cells[x, y].Value = rnd;
UnityEngine.Debug.Log(x.ToString() + " " + y.ToString());
}
}
UnityEngine.Debug.Log("Process finsihed ");
}
}
The error is coming from line 38
_cells[x, y].Value = rnd;
I've created a script called Debug and I generate the Grid object in start(), not I've switched up the code a bit while trying to figure out what was going wrong...
void Start () {
SudokuGrid grid = new SudokuGrid ();
//grid.Generate ();
grid.Cells [2, 3].Value = 5;
UnityEngine.Debug.Log (grid.Cells [2, 3].Value.ToString ());
}
Hi, you instantiate an array of Cells. This is correct but the elements of the array are Cell reference or pointer, but they are each empty = null after the array is instantiated.
You need to instantiate a new Cell() for each element of the array!
If it was a value type like an int or a struct you wouldn't need to do that, but as it is a class, they need to be instantiated one by one.
Thanks for the reply.
However I tried this and I'm still getting the same error. I've tried adding this to both the constructor and the Generate() method and neither worked.
for (int x = 0; x < 9; x++) {
for (int y = 0; y < 9; y++) {
_cells[x, y] = new Cell();
}
}
The SudokuGrid constructor should be the place to do it, and your code seems correct.
On the line "public class Cell : iCell", what is this iCell it derives from ?
iCell is the interface for the Cell class.
I'll have another crack at it when I get home from work.
Ho, on line 23 "Cell [,] _cells = new Cell[9,9];": a new _cell[,] is created that is not the private member _cell and is deleted at the constructor's exit... That's why _cell itself is null later in Generate(). I guess that's your first bug. Not instantiating a cell for each element of the array would have cause further errors as well :)
