GameObject is not reading the rigidbody2D component of instantiated prefab,GameObject is not reading the Rigidbody2D component from instantiated prefab

Question

I am making a Pong game to practice Unity. I have a GameManagerPong.cs that spawns in the ball.

 public class GameManagerPong : MonoBehaviour
 {
     public GameObject ballPrefab;
     // Start is called before the first frame update
     void Start()
     {
         Instantiate(ballPrefab, new Vector2(0, 0), Quaternion.identity);
     }
     
     public void SpawnBall()
     {
         StartCoroutine(ballTimer());
     }
 
     IEnumerator ballTimer()
     {
         yield return new WaitForSeconds(1.5f);
         Instantiate(ballPrefab, new Vector2(0, 0), Quaternion.identity);
     }
 }

I also have a ball prefab w$$anonymous$$ch has a Rigidbody2D component. I have two paddles in the scene. Paddle1(player paddle) and paddle2(AI paddle) Paddle2 has public gameObject reference to the prefab Ball.

alt text

Also t$$anonymous$$s is the code in the ComputerPaddle script

 public class ComputerPaddle : Paddle
 {
     public GameObject ball;
     private Rigidbody2D rbBall;
 
     [Tooltip("Larger number makes the paddle react more slowly")]
     public float computerMoveThreshold = 3.0f; //increase number to make paddle move with delay
 
     private void Start()
     {
         rbBall = ball.GetComponent<Rigidbody2D>();
     }
     private void FixedUpdate()
     {
         Debug.Log(rbBall.velocity); //t$$anonymous$$s just returns (0.0, 0.0)
         if (t$$anonymous$$s.rbBall.velocity.x > 0.0f && t$$anonymous$$s.rbBall.position.x > computerMoveThreshold)
         {
             if (t$$anonymous$$s.rbBall.position.y > t$$anonymous$$s.transform.position.y)
             {
                 rb.AddForce(Vector2.up * t$$anonymous$$s.speed);
             }
             else if (t$$anonymous$$s.rbBall.position.y < t$$anonymous$$s.transform.position.y)
             {
                 rb.AddForce(Vector2.down * t$$anonymous$$s.speed);
             }
         }
         else
         {
             if(t$$anonymous$$s.transform.position.y > 2.0f)
             {
                 rb.AddForce(Vector2.down * t$$anonymous$$s.speed);
             }
             else if(t$$anonymous$$s.transform.position.y < -2.0f)
             {
                 rb.AddForce(Vector2.up * t$$anonymous$$s.speed);
             }
         }
     }
 }

At first I just tried making a public Rigidbody2D variable and dragged the Ball prefab on there and it still didn't work. T$$anonymous$$s version also doesn't work. T$$anonymous$$s may be a simple fix but I'm a bit stumped. Any help is appreciated. Thank you!

Answer 1

You can t$$anonymous$$nk of a prefab like a GameObject that doesn't exist in a scene. It exists somewhere, but not in any place that it can interact with anyt$$anonymous$$ng. When you Instantiate a prefab, you are making a copy of it that does exist in the scene. In fact, you can make as many copies of t$$anonymous$$s object as you want in the scene.

So if you have a reference to a prefab then you instantiate that prefab, your reference is still the original prefab object, NOT the one that was just copied into the scene, w$$anonymous$$ch is what you want. So how do you get a reference to the instance of the prefab?

Well, there are a million different ways. The easiest way is for whatever object is spawning the ball (your game manager in t$$anonymous$$s case) to just keep track of the ball, and give out references whenever another script asks.

 public GameObject theBallInstance;
 theBallInstance = Instantiate(ballPrefab...);
 ...
 //Get the ball instance from another script
 GameObject theBall = gameManager.theBallInstance;

Just make sure that the ball is actually instantiated before you ask the game manager for the ball instance ($$anonymous$$nt - put your Instantiate call in Awake, because your other script is accessing the ball on Start).

You can also use calls like GameObject.Find, GameObject.FindObjectOfType, to dynamically find objects or components in a scene, but keep in mind that these are expensive and shouldn't be called every frame.

GameObject is not reading the rigidbody2D component of instantiated prefab,GameObject is not reading the Rigidbody2D component from instantiated prefab

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