Unable to destroy collider Unity3d

Question

So I was making an android game in unity3d. I wrote a script to draw straight lines with touch what I do is I first create a gameobject named temp and add line renderer to it and give the line renderer properties. Then I create a collider gameobject , parent it to the line and change its dimensions to the dimension of the line. What I am trying to do is add two colliders one while the line is being moved i.e "touch.phase == TouchPhase.Moved" and delete this collider and add another collider when "touch.phase == TouchPhase.Ended". For some weird reasons I am not able to delete the first collider.

Here is my code

void Update()
{

    foreach (Touch touch in Input.touches)
    {

        if (touch.phase == TouchPhase.Began)
        {
            temp = new GameObject();
            temp.AddComponent<LineRenderer>();
            temp.layer = LayerMask.NameToLayer("lines");


            lr = temp.GetComponent<LineRenderer>();
            lr.positionCount = 2;
            lr.SetWidth(0.2f, 0.2f);
            lr.material = new Material(Shader.Find("Sprites/Default"));
            lr.SetColors(Color.black, Color.black);

            temp.transform.position = camera.ScreenToWorldPoint(touch.position) + camOffset;
            fingerUp = camera.ScreenToWorldPoint(touch.position)+camOffset;

            lr.useWorldSpace = true;
            spawnCollider = false;



        }

        //Detects Swipe while finger is still moving
        if (touch.phase == TouchPhase.Moved)
        {
            lr.SetPosition(0, fingerUp);
            fingerDown = camera.ScreenToWorldPoint(touch.position)+camOffset;
              lr.SetPosition(1,fingerDown);
            spawnCollider = true;

            lastLine = temp;

            // The first collider temporary one

            BoxCollider2D col1 = new GameObject().AddComponent<BoxCollider2D>();
            col1.transform.parent = temp.transform;
            float lineLength = Vector2.Distance(fingerUp, fingerDown);
            col1.size = new Vector2(lineLength, 0.2f);
            Vector2 midPoint = (fingerUp + fingerDown) / 2;
            col1.transform.position = midPoint;
            float angle = (Mathf.Abs(fingerDown.y - fingerUp.y) / Mathf.Abs(fingerDown.x - fingerUp.x));
            if ((fingerUp.y < fingerDown.y && fingerUp.x > fingerDown.x) || (fingerDown.y < fingerUp.y && fingerDown.x > fingerUp.x))
            {
                angle *= -1;
            }
            angle = Mathf.Rad2Deg * Mathf.Atan(angle);
            col1.transform.Rotate(0, 0, angle);

        }

        if (touch.phase == TouchPhase.Ended)
        {
            if (spawnCollider == true)
            {  
                Destroy(col1);  // Deleting the first collider

                // Adding the final collider 
                BoxCollider2D col = new GameObject("Collider").AddComponent<BoxCollider2D>();
                col.transform.parent = temp.transform;
                float lineLength = Vector2.Distance(fingerUp, fingerDown);
                col.size = new Vector2(lineLength, 0.2f);
                Vector2 midPoint = (fingerUp + fingerDown) / 2;
                col.transform.position = midPoint;
                float angle = (Mathf.Abs(fingerDown.y - fingerUp.y) / Mathf.Abs(fingerDown.x - fingerUp.x));
                if ((fingerUp.y < fingerDown.y && fingerUp.x > fingerDown.x) || (fingerDown.y < fingerUp.y && fingerDown.x > fingerUp.x))
                {
                    angle *= -1;
                }
                angle = Mathf.Rad2Deg * Mathf.Atan(angle);
                col.transform.Rotate(0, 0, angle);
            }
        }




    }


}

I have added comments where I am doing what.

Answer 1

I assume that col1 is also declared elsewhere in the code, otherwise I don't understand how this would've compiled.

Notice this line:

BoxCollider2D col1 = new GameObject().AddComponent<BoxCollider2D>();

You're re-declaring col1 within a limited scope, and so you're not setting the external col1, which is used when the touch phases ends. Use

col1 = new GameObject().AddComponent<BoxCollider2D>();

Instead, and it should work, although you will get a new collider on every move, which sounds excessive.

On a side note, try to avoid calls to AddComponent/GetComponent in the Update() method - it will incur a significant performance hit. These should be cached in a local field once, instead of queried repeatedly. Also, avoid creating temporary game objects.

I'm not near a work machine, so I haven't tested this code, and it'll probably need some adjustment for it to compile, but I think it shows the gist of my suggestion.

GameObject temp;
private LineRenderer lr;
private BoxCollider2D move_collider;
private BoxCollider2D final_collider;

void Start() {
    temp = new GameObject();
    lr = AddComponent<LineRenderer>();
    lr.positionCount = 2;
    lr.SetWidth(0.2f, 0.2f);
    lr.material = new Material(Shader.Find("Sprites/Default"));
    lr.SetColors(Color.black, Color.black);
    temp.layer = LayerMask.NameToLayer("lines");
    lr.useWorldSpace = true;
    move_collider = temp.AddComponent<BoxCollider2D>();

}

void Update()
{
    foreach (Touch touch in Input.touches)
    {

        if (touch.phase == TouchPhase.Began)
        {
            temp.transform.position = camera.ScreenToWorldPoint(touch.position) + camOffset;
            fingerUp = camera.ScreenToWorldPoint(touch.position)+camOffset;
            move_collider.enabled = true;
            final_collider.enabled = false;
        }

        //Detects Swipe while finger is still moving
        if (touch.phase == TouchPhase.Moved)
        {
            lr.SetPosition(0, fingerUp);
            fingerDown = camera.ScreenToWorldPoint(touch.position)+camOffset;
              lr.SetPosition(1,fingerDown);

            lastLine = temp;

            float lineLength = Vector2.Distance(fingerUp, fingerDown);

            move_collider.size = new Vector2(lineLength, 0.2f);
            Vector2 midPoint = (fingerUp + fingerDown) / 2;
            move_collider.transform.position = midPoint;
            float angle = (Mathf.Abs(fingerDown.y - fingerUp.y) / Mathf.Abs(fingerDown.x - fingerUp.x));
            if ((fingerUp.y < fingerDown.y && fingerUp.x > fingerDown.x) || (fingerDown.y < fingerUp.y && fingerDown.x > fingerUp.x))
            {
                angle *= -1;
            }
            angle = Mathf.Rad2Deg * Mathf.Atan(angle);
            move_collider.transform.Rotate(0, 0, angle);
        }

        if (touch.phase == TouchPhase.Ended)
        {
            if (spawnCollider == true)
            {  
                move_collider.enabled = false;
                final_collider.enabled = true;

                // Adding the final collider 
                final_collider.transform.parent = temp.transform;
                float lineLength = Vector2.Distance(fingerUp, fingerDown);
                final_collider.size = new Vector2(lineLength, 0.2f);
                Vector2 midPoint = (fingerUp + fingerDown) / 2;
                final_collider.transform.position = midPoint;
                float angle = (Mathf.Abs(fingerDown.y - fingerUp.y) / Mathf.Abs(fingerDown.x - fingerUp.x));
                if ((fingerUp.y < fingerDown.y && fingerUp.x > fingerDown.x) || (fingerDown.y < fingerUp.y && fingerDown.x > fingerUp.x))
                {
                    angle *= -1;
                }
                angle = Mathf.Rad2Deg * Mathf.Atan(angle);
                final_collider.transform.Rotate(0, 0, angle);
            }
        }
    }
}