I am trying to create a Sudoku in WinForms with C# as a school assignment. Everything in the sudoku MUST be object oriented so I have not chosen to structure the code like this, the teacher did.
When I put a number(int) in a Textbox in the SudokuGUI, it tries to put the number in the arrays but fails and give me the error well known:
An unhandled exception of type 'System.NullReferenceException' occurred in WindowsFormsApplication5.exe Additional information: Object reference not set to an instance of an object.
This is how the code look like:
First we send the Number when keyreleased from the TextBox to the method that will put the number in to the array
private void Valuechange_KeyUp(object sender, KeyEventArgs e)
{
TextBox text_box = sender as TextBox;
var position = tableLayoutPanel1.GetPositionFromControl(text_box);
int x = position.Row;
int y = position.Column;
if (int.TryParse(text_box.Text, out value) && int.Parse(text_box.Text) < 10 && int.Parse(text_box.Text) > 0 || value == 0)
{
add_value.Array_AddNumber(x, y, value);
}
else
{
MessageBox.Show("Skriv in en siffra mellan 1-9");
text_box.Clear();
}
}
Here is the method that will add the number from Textbox to the Array that will hold the numbers
class Ruta
{
Siffra number = new Siffra();
public Siffra[,] SudokuArray = new Siffra[9, 9];
public void Array_AddNumber(int x, int y, int value)
{
SudokuArray[x, y].nummer = value;
}
}
And here is the "Siffra" which means Number in Swedish, that is the the type of the Array
class Siffra
{
private int _nummer;
public int nummer
{
get { return _nummer; }
set { _nummer = value; }
}
}
What have I done wrong, I really don't understand, my teacher couldn't even help me :/
Here is the whole solution: https://dl.dropboxusercontent.com/u/13409794/WindowsFormsApplication5.zip
The problem is a misunderstanding of this line:
public Siffra[,] SudokuArray = new Siffra[9,9];
That line creates a new 2-dimensional array object in memory, with space for 9 items x 9 items (81 in total). The misunderstanding is that the contents of each spot in the array is still null. Therefore, later on in your code, when you do this:
SudokuArray[x,y].nummer = value;
The code first looks up the array reference and uses that to find the element at position (x,y). That value is still null. The code then ties to use the nummer property of a null reference. Oops. You can't do that.
To fix it, you need to add this code to the constructor for your Ruta class:
for (int x = 0; x < 9; x++)
for (int y = 0; y < 9; y++)
SudokuArray[x,y] = new Siffra();
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