Object reference not set to instance of an object?

Question

Hello, I am attempting to make it so that once a trigger is entered, a Boolean value would be set to true. After that, an if statement in another script should allow me to shoot green balls. Here is the code:

The Trigger Script: using UnityEngine; using System.Collections;

 public class player_gun_manager_script : MonoBehaviour {
 
     public bool green = false;
 
     void OnTriggerEnter(Collider other) {
         if (other.gameObject.name == "gun_model_green")
         {
             green = true;
         }
         else
         {
             green = false;
         }
     }
 
 }

The Shooting Script: using UnityEngine; using System.Collections;

 public class player_gun_script : MonoBehaviour {
 
     public GameObject gun_green;
     public float thrust_green = 50;
     player_gun_manager_script hasGun;
 
     void Start () {
         hasGun = GetComponent<player_gun_manager_script>();
     }
 
 
     void Update () {
 
         if (hasGun.green == true && Input.GetMouseButtonDown(0)) {// <------Error here
             GameObject green = (GameObject)Instantiate(gun_green, Camera.main.transform.position + Camera.main.transform.forward, Quaternion.identity);
             green.GetComponent<Rigidbody>().AddForce(Camera.main.transform.forward * thrust_green, ForceMode.Impulse); 
             
         }
     
     }
 
 }

All looks good except the following error:

NullReferenceException: Object reference not set to an instance of an object player_gun_script.Update () (at Assets/scripts/player_gun_script.cs:17)

The problem seems to be on line 17 of the gun script, but I can't make out what the issue is... please help. Thank You :)

Answer 1

Best Answer

Answer by TBruce · May 23, 2016 at 06:33 PM

The problem is you are missing a player_gun_manager_script component. Below fixes your error and prints a debug warning

 public class player_gun_script : MonoBehaviour
 {
     public GameObject gun_green;
     public float thrust_green = 50;
     player_gun_manager_script hasGun;
 
     void Start ()
     {
         // if hasGun has not yet been set in the inspector see if there is one attched to the current component
         if ((hasGun == null) && (GetComponent<player_gun_manager_script>() != null))
         {
             hasGun = GetComponent<player_gun_manager_script>();
         }
         else
         {
             Debug.LogWarning("Missing player_gun_manager_script component. Please add one");
         }
     }
 
 
     void Update ()
     {
         if ((hasGun != null) && (hasGun.green == true) && (Input.GetMouseButtonDown(0)))
         {
             GameObject green = (GameObject)Instantiate(gun_green, Camera.main.transform.position + Camera.main.transform.forward, Quaternion.identity);
             green.GetComponent<Rigidbody>().AddForce(Camera.main.transform.forward * thrust_green, ForceMode.Impulse); 
         }
     }
 
 }

Note: Your code was doing this

 hasGun = GetComponent<player_gun_manager_script>();

If you had already set hasGun in the inspector you would be nullifying the value with the statement above.

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aurreco · May 23, 2016 at 07:00 PM 0

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Hi, thank you for letting me know what the problem is. However, I cannot figure out why Unity thinks the component is not attached. alt text

This is the inspector view of the player object, and, as you can see, it does have the component player_gun_manager_script attached. Please help me figure out the solution to this. Thank you.

Also, I do not believe I had set hasGun to a value in the inspector.

inspector-view.png (100.5 kB)

TBruce aurreco · May 24, 2016 at 02:00 AM 0

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hasGun is a private field so you can not set it in the inspector. You are showing me the object that the player_gun_manager_script is attached to but I see no player_gun_script. So when you go to get the component like this

 hasGun = GetComponent<player_gun_manager_script>();

you will error. Where is the object that has the player_gun_script?

This is the script that defines

 public GameObject gun_green;
 public float thrust_green = 50;
 player_gun_manager_script hasGun;

and calls

 hasGun = GetComponent<player_gun_manager_script>();

On the GameObject that has the player_gun_script attached you need to do one of three things

Add the player_gun_manager_script to the same GameObject as the one the player_gun_script is on.
$$anonymous$$ake hasGun a public and set it in the inspector.
Search for the GameObject that has the player_gun_manager_script attached to it in the player_gun_script.

aurreco TBruce · May 26, 2016 at 01:52 PM 0

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Thank you for helping (my apologies for getting back to you so late)

I did as told and now I receive no error and everything is working! I appreciate the help :)

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Object reference not set to instance of an object?

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