Draw Trajectory in Sceneview

Hi folks,

I did a simple code to draw a trajectory of a gameObject whenever I move it. But, the trajectory was not drawn. was wondering what might be the mistake. Here is the snippet code

 using UnityEngine;
 using System.Collections;
 
 public class Trajectory : MonoBehaviour {
 
     public Color rayColor = Color.blue;
     Vector3 currentPos;
 
     Vector3 prev;
     bool flag = false;
 
 
     void OnDrawGizmos(){
 
         if (!flag) {
             prev = transform.position;
             flag = true;
         }
         
         if (transform.hasChanged){
             Gizmos.color = rayColor;
             currentPos = transform.position;
             transform.hasChanged = false;
 
 
         }
         Debug.Log ("prev: " + prev);
         Debug.Log ("curr: " + currentPos);
         
         Gizmos.DrawLine (prev, currentPos);
         prev = currentPos;
 
     }
 }
 

From debug info, I saw the prev and curr were different but line was not drawn. Does anyone can help to figure out why this code does not work?

Thanks in advance.