(Unity) Drag and detect object below when dropping

For getting all the colliders which are below the touch position , we need to use the RaycastAll function.

This returns an array of hits from which we can determine the GameObject which is at the farthest distance from the camera.

Also take care of the situation where no objects where detected, to avoid the null reference error.

void Update() 
    {
        if (Input.GetMouseButtonUp (0)) 
        {
            RaycastHit[] hits;
            Ray camRay = Camera.main.ScreenPointToRay(Input.mousePosition);
            hits = Physics.RaycastAll (camRay);

            Debug.Log("hits "+hits.Length);
            GameObject LastGameObject = null;

            for (int i = 0; i < hits.Length; i++) 
            {
                RaycastHit hit = hits [i];

                if(LastGameObject == null)
                {
                    LastGameObject =  hit.transform.gameObject;

                }
                else 
                {

                    if(Vector3.Distance (LastGameObject.transform.position,Camera.main.transform.position) < Vector3.Distance (hit.collider.transform.position,Camera.main.transform.position))
                    {
                        LastGameObject =  hit.transform.gameObject;
                    }
                }

            }

            if(LastGameObject)
                Debug.Log("last "+LastGameObject.name);
        }


    }