Instantiated Prefab no Rigidbody2D on Update function

Question

Hey there,

I have the following situation:

I got a GameplayManager script like this:

 public class GameplayManager : MonoBehaviour
 {
     public Transform spawnPoint1;
     public Rigidbody2D player;
 
     void Start()
     {
         Instantiate (player, spawnPoint1.position, spawnPoint1.rotation);
     }
 
         ....
 }

There is a prefab assigned to the "player" variable there is an empty gameobject assigned to the spawnPoint1 variable.

This script-component(GameplayManager) is attached to the camera component.

On my "player" prefab i assigned a new script component "PlayerManager":

 public class PlayerManager : MonoBehaviour
 {
     Rigidbody2D rb2d;
 
     void Start()
     {
         rb2d = GetComponent<Rigidbody2D> ();
     }
 
     void Update()
     {
         
     }
 
     public void Jump()
     {
         rb2d.AddForce (new Vector2 (rb2d.velocity.x, 500f));
     }
 
     ...
 }

Next i added a Button to my canvas and assigned a Event Trigger: Value: "Player" Prefab Select: PlayerManager.Jump()

When i press the button in the game, no force is applied to the rigidbody of the player prefab.

I simply dont know why..any help or advices?

Thansks and Greetings

Answer 1

Best Answer

Answer by incorrect · May 04, 2016 at 02:18 PM

You should understand the difference between a prefab and it's instance. A prefab is just a prototype that exists in a memory but not in a scene. An instance is a copy built from this prototype and placed into the scene.

So if you are calling a method on a prefab you are not calling a method on an actual instance you've created using Instantiate().

To call a method on the instance of the prefab you need to store a reference to this copy an use it like reference.method();

Try saving a reference when you instantiate the prefab in GameplayManager and assign it's method to the button:

 [SerializeField]
 private UnityEngine.UI.Button button;
 
 void Start()
 {
     //saving reference to a copy created
     GameObject instance = Instantiate (player, spawnPoint1.position, spawnPoint1.rotation) as GameObject;
         
     //getting PlayerManager on this copy
     PlayerManager pManager = instance.GetComponent<PlayerManager>();
         
     //if there is a PlayerManager on this copy
     if(pManager != null)
         //assign instance's method to the button onClick delegate
         button.onClick.AddListener(pManager.Jump);
 }

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brudi · May 04, 2016 at 06:24 PM 0

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thanks this was my mistake, i will still have to deal with some game logics in the future:)

brudi · May 04, 2016 at 09:34 PM 0

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But i still have a question... when i call Jump method, the rigidbody still needs to be created in "PlayerManager" right, and in this case its unassigned... any advices?

Between: Shouldnt you change

 button.onClick.AddListener(instance.Jump);

to:

 button.onClick.AddListener(pManager.Jump);

?

incorrect brudi · May 04, 2016 at 09:50 PM 1

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Yes, my bad. button.onClick.AddListener(pManager.Jump); is the right one. I'll edit my answer, thnx.

You don't need to create RigidBody2D if your prefab GameObject has this component. As I understand, you also have PlayerManager component on this prefab.

Your PlayerManager has Start() method that is executed once object is created. This code actually find a reference to the Rigidbody2D and saves it into rb2d variable.

   rb2d = GetComponent<Rigidbody2D> ();

So when Jump() is called, you already have a reference to rigidbody.

brudi incorrect · May 05, 2016 at 12:00 PM 0

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do i need this line:

 button.onClick.AddListener(pManager.Jump);

or can i just apply an "event trigger" to the button in the canvas?

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Instantiated Prefab no Rigidbody2D on Update function

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