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Question by Towsif-Khan · Aug 17, 2018 at 10:39 PM · programmingupdatenullreferenceexceptioninheritance

Object Reference to a global private variable is set in Awake function but lost in another function in the same class.

please look at the comments in the code provided for a better understanding of the problem.

Object reference is set in CharacterMovementModel.Awake() and as expected Debug.Log(m_Attributes) prints the gameObject name with the component name.

The Update function in JellyMovementModel, which inherits from CharacterMovementModel() also prints expected results when Debug.Log(m_Attributes) is used.

But when the CharacterMovementModel.UpdateMovement() is called from JellyMovementModel.Update() Debug.Log(m_Attributes) prints "NULL".

I found a "non graceful" work around. Setting the reference to m_Attributes right before it is used in CharacterMovementModel.UpdateMovement(). UpdateMovement() is only ever called from JellyMovementModel.Update() and hence I am not fond of it.

I do not understand how the work around works or how it doesn't work without the work around.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class CharacterMovementModel : MonoBehaviour
 {
     protected float m_speed;
 
     protected Rigidbody2D m_Body;
     protected CharacterAttributes m_Attributes;
 
     protected Vector2 m_MovmentDirection;
     private Vector2 m_RecievedDirection;
     private Vector2 m_FacingDirection;
 
     protected void Awake()
     {
         m_Attributes = GetComponent<CharacterAttributes>();
         m_Body = GetComponent<Rigidbody2D>();
         m_speed = m_Attributes.getSpeed();
 
         //this Returns the correct component of the corrent game object.
         Debug.Log(m_Attributes);
     }
 
     //this function is called from the class which inherits from this class
     protected void UpdateDirection()
     {
         //this Returns NULL
         Debug.Log(m_Attributes);
 
         m_MovmentDirection = new Vector2(m_RecievedDirection.x, m_RecievedDirection.y);
 
         if (m_RecievedDirection != Vector2.zero)
         {
             Vector2 facingDirection = m_MovmentDirection;
 
             if (facingDirection.x != 0 && facingDirection.y != 0)
             {
                 if (facingDirection.x == m_FacingDirection.x)
                 {
                     facingDirection.y = 0;
                 }
                 else if (facingDirection.y == m_FacingDirection.y)
                 {
                     facingDirection.x = 0;
                 }
                 else
                 {
                     facingDirection.x = 0;
                 }
             }
 
 
             m_FacingDirection = facingDirection;
         }
     }
 
     protected void ResetRecievedDirection()
     {
         m_RecievedDirection = Vector2.zero;
     }
 
     private void UpdateHit()
     {
 
     }
 
     virtual protected void UpdateMovement()
     {
         if (PlayerAttributes.instance.IsGameStateFrozen())
         {
             m_MovmentDirection = Vector2.zero;
         }
 
         if (m_MovmentDirection != Vector2.zero)
         {
             m_MovmentDirection.Normalize();
         }
 
         m_Body.velocity = m_MovmentDirection * m_speed;
     }
 
     
 
     public Vector2 GetFacingDirection()
     {
         return m_FacingDirection;
     }
 
     public bool IsMoving()
     {
         return m_MovmentDirection != Vector2.zero;
     }
 
     public void SetDirection(Vector2 direction)
     {
         if (direction == Vector2.zero)
         {
             return;
         }
 
         m_RecievedDirection = direction;
     }
 
     public virtual void DoAction()
     {
 
     }
 
     public void GetHit()
     {
         
     }
 }



 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class JellyMovementModel : CharacterMovementModel
 {
     protected void Update()
     {
         if (PlayerAttributes.instance.IsGameStateFrozen())
             return;
 
         //this Returns the correct component of the corrent game object.
         Debug.Log(m_Attributes);
 
         //this is a function from the base class but does not have the reference to m_Attributes
         UpdateDirection();
         ResetRecievedDirection();
     }
 
     protected void FixedUpdate()
     {
         UpdateMovement();
     }
 }

Pre thanks :)

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