Problem with scopes? "Object reference not set to an instance of an object "

Question

I'm trying to build a 3D Spectograph and get a bunch of frequency data for a given point in time. I need to simplify this in order to be able to handle the instantiating of a lot of prefabs. So I use a fixed count of Rows of fequency data to look at:

int spectrumRows = 24;

I then call this function to "simplify" the detail of the frequency spectrum by adding values together and then just adding their median to a float array called "floatArray". This then is passed to another float array, "simpleSpectrum", which tells me that there is this reference error.

public void addToSimpleSpectrum(float[] spectrum) {
    float spectralsInRow = spectrum.Length / spectrumRows;
    Math.Round(spectralsInRow);
    float[] floatArray = new float[(int)spectralsInRow];
    for(int i = 0; i < spectralsInRow; i++){    
        float median = 0f;
        float sum = 0f;
        for (float o = spectralsInRow*i; o < (spectralsInRow*(i+1)); o++) {
            sum = sum + spectrum[(int)o];
        }
        median = sum / spectralsInRow;  
        floatArray[i] = median;
    }   
    simpleSpectrum.Add(floatArray);
}

The error I'm getting in Unity is:

System.NullReferenceException: Object reference not set to an instance of an object at [...]:46

Which means that the "simpleSpectrum.Add(floatArray);" doesn't work because it doesn't know what the floatArray is. The "public List<float[]> simpleSpectrum" is created in global scope. But the floatArray should be accessible within the function, or not?

I hope somebody can help me. C# is new to me!

`Math.Round(spectralsInRow);` is a no-op as you are not saving the result. `simpleSpectrum` needs an assigned value somewhere `= new List()`. I suggest you read up on how assignments work. — Charlieface, Jan 04 '21 at 23:33
Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Charlieface, Jan 04 '21 at 23:33
Also, after rounding `spectralsInRow` you can store it in an `int` to save converting it every time — Charlieface, Jan 04 '21 at 23:34
Hang on there. The error means that the object being referenced, which is to say `simpleSpectrum`, is null. It has nothing to do with the value of `floatArray`. — Ruzihm, Jan 04 '21 at 23:58

score 1 · Accepted Answer · answered Jan 04 '21 at 23:38

Please make it:

private  List<float[]> _simpleSpectrum = new List<float>();

Or if you need to access it outside the class:

public List<float[]> SimpleSpectrum { get; set; }

This way it will a) work and b) be aligned with standard C# naming convention

passed to another float array, "simpleSpectrum"

Be careful using the words "array" and "list" - other developer professionals will expect you to really actually be using those things if that's what you say. SimpleSpectrum is a list, not an array. A fellow C# dev would be very confused if you insisted it was an array and then showed some code where you called an Add method on it

Problem with scopes? "Object reference not set to an instance of an object "

1 Answers1