C# object null reference exception - not sure how to set array values

Question

I guess I'm not setting the array correctly or something, but this throws a "nullreferenceexception" when it gets to the line where it actually sets the new array value to the color_table array (should be the 7th and 12th lines of what you see below). How should I write this so that it works?

public int[] colors = new int[] { 0, 255, 0, 255, 0, 255 };

private int[][] color_table;

public void setcolors()
{
    this.color_table[0] = new int[] { 0, 0, 0 };
    for (int i = 1; i <= this.precision; i++) {
        int r = (((this.colors[1] - this.colors[0]) * ((i - 1) / (this.precision - 1))) + this.colors[0]);
        int g = (((this.colors[3] - this.colors[2]) * ((i - 1) / (this.precision - 1))) + this.colors[2]);
        int b = (((this.colors[5] - this.colors[4]) * ((i - 1) / (this.precision - 1))) + this.colors[4]);
        this.color_table[i] = new int[] { r, g, b };
    }
}

I've heard something about that you MUST initialize an array with its length before using it, but a) I don't know how to do that and b) I'm not sure if it's problem. The issue there is that I don't know what the array length is going to be. I tried this to no avail:

private int[this.precision][3] color_table;

Thanks!

Your color_table is never initialized to any length... You should consider declaring it as [this.precision+1][3] — Ravi Y
– Ravi Y, Commented Dec 28, 2012 at 8:18
It underlines the [3] in red and says Invalid rank specifier: expected ',' or ']' ... That's what I had tried before that didn't work. — stingray-11
– stingray-11, Commented Dec 28, 2012 at 8:25
@user1653653: You should leave the second arrays empty as in my example. — jgauffin
– jgauffin, Commented Dec 28, 2012 at 8:27

jgauffin · Accepted Answer · 2012-12-28 08:23:10Z

3

this.color_table has not been initialized. Hence you can't assign values to it.

Did you mean something like this:

public void setcolors()
{
    color_table = new int[precision + 1][];
    for (int i = 1; i <= this.precision; i++)
    {
        int r = (((this.colors[1] - this.colors[0]) * ((i - 1) / (this.precision - 1))) + this.colors[0]);
        int g = (((this.colors[3] - this.colors[2]) * ((i - 1) / (this.precision - 1))) + this.colors[2]);
        int b = (((this.colors[5] - this.colors[4]) * ((i - 1) / (this.precision - 1))) + this.colors[4]);
        this.color_table[i] = new int[] { r, g, b };
    }
}

answered Dec 28, 2012 at 8:23

jgauffin

101k45 gold badges245 silver badges378 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

stingray-11 Over a year ago

Thanks that worked :) I didn't know you had to leave the second array empty and then my other problem was that I was trying to declare it outside of a method.

jgauffin Over a year ago

You have to declare it in the constructor (or a method) unless precision is a constant (private const int precision = 4;)

king · Accepted Answer · 2012-12-28 08:29:35Z

0

try to use list if you don't know the length of your array

    List<int[]> color_table = new List<int[]>();
...
    color_table.Add(new int[] { r, g, b });

answered Dec 28, 2012 at 8:29

king

3041 silver badge8 bronze badges

Collectives™ on Stack Overflow

C# object null reference exception - not sure how to set array values

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related