Trying to draw lines using LineRenderer from tower to spawners

Question

So I have a tower surrounded by 4 spawner gameobjects. I want to draw lines to all of them using LineRenderer. I wrote the following code to achieve this but for some reason I am getting NullReferenceException: Object reference not set to an instance of an object at the line myLines[i].transform.position = startPos;

public Transform towerPos;
GameObject[] myLines;

void DrawLines()
        {
            myLines = new GameObject[spawnpoints.Count];
            Vector3 startPos = towerPos.transform.position;
            for (int i = 0; i < spawnpoints.Count; i++)
            {

                myLines[i].transform.position = startPos;
                myLines[i].AddComponent<LineRenderer>();
                LineRenderer lr = myLines[i].GetComponent<LineRenderer>();
                lr.material = new Material(Shader.Find("Particles/Alpha Blended Premultiply"));
                lr.SetColors(Color.red, Color.red);
                lr.SetWidth(0.3f, 0.3f);
                lr.SetPosition(0, startPos);
                lr.SetPosition(1, spawnpoints[i].spawnPoint.transform.position);
                //GameObject.Destroy(myLine, duration);
            }
        }

The above function is called at Start(). The tower GameObject is dragged into the towerPos variable in the editor so dont know why its a null.

Answer 1

In C#, new SomeReferenceType[length] doesn't create length number of objects of type SomeReferenceType. It creates an Array that could hold that many SomeReferenceType references, but initially contains nothing.

So, if you want to fill that array with actual objects, you need to assign them.

void DrawLines()
{
    myLines = new GameObject[spawnpoints.Count];
    Vector3 startPos = towerPos.transform.position;

    // Cache your material so you don't need to make so many copies.
    var material = new Material(Shader.Find("Particles/Alpha Blended Premultiply"));

    for (int i = 0; i < spawnpoints.Count; i++)
    {
        // FIRST: Create & assign your GameObject into the array slot.
        var lineObject = new GameObject("Line" + i);
        myLines[i] = lineObject;


        lineObject.transform.position = startPos;
        LineRenderer lr = lineObject.AddComponent<LineRenderer>();

        // No need to search for the component we just added!
        // LineRenderer lr = myLines[i].GetComponent<LineRenderer>();

        // Use sharedMaterial to be batching-friendly and avoid excess allocation.
        lr.sharedMaterial = material;

        lr.SetColors(Color.red, Color.red);
        lr.SetWidth(0.3f, 0.3f);
        lr.SetPosition(0, startPos);
        lr.SetPosition(1, spawnpoints[i].spawnPoint.transform.position);
    }
}