Destroy collectible (e.g. coin) on collision

Hi people, I have a collision system in which if the player collides with a collectible coming towards them from the right hand side (parralaxed objects) then they gain a point. However the collectible currently does not disappear, the user simply faces through it and gets their point. I would like to change this so that the collectible disappears.

I can get the user/character to disappear on collision however if i use

Code (CSharp):

1.  
2.     void OnTriggerEnter2D(Collider2D col)
3.     {
4.         if (col.gameObject.tag == "Collectible")
5.         {
6.             PlayerScored();
7.             Destroy(col.gameObject);
8.         }
9.         if (col.gameObject.tag == "Death")
10.         {
11.             rigidbody.simulated = false;
12.             PlayerDied();
13.         }
14.  
15.     }
16.  
17. }
18.  

the Destroy(col.gameObject); line destroys every instance of the object resulting in this error:

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Transform.get_localPosition () (at C:/buildslave/unity/build/artifacts/generated/common/runtime/TransformBindings.gen.cs:41)
Parallaxer.Shift () (at Assets/scripts/Parallaxer.cs:140)
Parallaxer.Update () (at Assets/scripts/Parallaxer.cs:88)

If I change it to Destroy(gameObject); the player is destroyed instead but no errors occur and the game continues. If i remove the destroy line of code completely it returns to how I described it at the beginning, going through the collectible, getting the point but it does not disappear.

Does anyone have advice on how to get the single instance of the collectible to disappear without breaking it? I am a novice in Unity.

Many thanks.

 

You may need to make it a prefab by dragging it from the hierarchy into your assets folder. Then delete it, and drag the prefab onto a public variable to be instantiated.

 

Yah it is already a prefab as the parralaxing spawning of the collectible functions just the deletion of only one instance of it:

 

The error is a result of your Parallaxing script trying to access the coin after it has been destroyed. Because that script is maintaining its own list of game objects, it will need to be updated when an object on the list has been destroyed. The simple way would be to leave the list as is, and add a null check to the parallax script before it tries to modify any object on the list. You could also trigger an event when a coin is picked up, then the parallax script can listen for it and remove all destroyed objects when triggered.

Although, if it's a foreground object, why does the parallax script even need to know about the coin? Normally, foreground objects don't parallax and the camera movement is enough.

 

I think I understand what you are saying but unsure how to add a null check in the write place. The reason the collectibles are parallax is that they are randomly generating off screen in the same way as the background and the enemies. This is the parralax script:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Parallaxer : MonoBehaviour
6. {
7.  
8.     class PoolObject
9.     {
10.         public Transform transform;
11.         public bool inUse;
12.         public PoolObject(Transform t)
13.         {
14.             transform = t;
15.         }
16.         public void Use()
17.         {
18.             inUse = true;
19.         }
20.         public void Dispose()
21.         {
22.             inUse = false;
23.         }
24.     }
25.  
26.     [System.Serializable]
27.     public struct YSpawnRange
28.     {
29.         public float min;
30.         public float max;
31.     }
32.  
33.  
34.     public GameObject Prefab;
35.     public int poolSize;
36.     public float shiftSpeed; //how fast the object is moving
37.     public float spawnRate; //how often it spawns
38.  
39.     public YSpawnRange ySpawnRange;
40.     public Vector3 defaultSpawnPos; //its starting position
41.     public bool spawnImmediate; //whether it will spawn immediately
42.     public Vector3 immediateSpawnPos; //the immediate spawn position
43.     public Vector2 targetAspectRatio; //target aspect ratio, accessibility stuff
44.  
45.     float spawnTimer;
46.     float targetAspect;
47.     PoolObject[] poolObjects;
48.     GameManager game;
49.  
50.     void Awake() //for initialisation
51.     {
52.         Configure();
53.     }
54.  
55.     void Start() //initialisate game
56.     {
57.         game = GameManager.Instance;
58.     }
59.  
60.     void OnEnable()
61.     {
62.         GameManager.GameOverConfirmed += GameOverConfirmed;
63.     }
64.  
65.     void OnDisable()
66.     {
67.         GameManager.GameOverConfirmed -= GameOverConfirmed;
68.     }
69.  
70.     void GameOverConfirmed()
71.     {
72.         for(int i = 0; i < poolObjects.Length; i++)
73.         {
74.             poolObjects[i].Dispose();
75.             poolObjects[i].transform.position = Vector3.one * 1000; //off screen
76.         }
77.  
78.         if (spawnImmediate)
79.         {
80.             SpawnImmediate();
81.         }
82.     }
83.  
84.     void Update()
85.     {
86.         if (game.GameOver) return;
87.  
88.         Shift();
89.         spawnTimer += Time.deltaTime;
90.         if (spawnTimer > spawnRate)
91.         {
92.             Spawn();
93.             spawnTimer = 0;
94.         }
95.     }
96.  
97.     void Configure()
98.     {
99.         targetAspect = targetAspectRatio.x / targetAspectRatio.y;
100.         poolObjects = new PoolObject[poolSize];
101.         for (int i = 0; i < poolObjects.Length; i++)
102.         {
103.             GameObject go = Instantiate(Prefab) as GameObject;
104.             Transform t = go.transform;
105.             t.SetParent(transform); //has the parent of object script is linked to
106.             t.position = Vector3.one * 1000; //offscreen again to avoid user seeing it
107.             poolObjects[i] = new PoolObject(t);
108.         }
109.         if (spawnImmediate)
110.         {
111.             SpawnImmediate();
112.         }
113.     }
114.  
115.     void Spawn()
116.     {
117.         Transform t = GetPoolObject();
118.         if (t == null) return; //true means pool size is too small
119.         Vector3 pos = Vector3.zero;
120.         pos.x = (defaultSpawnPos.x * Camera.main.aspect)/targetAspect;
121.         pos.y = Random.Range(ySpawnRange.min, ySpawnRange.max);
122.         t.position = pos;
123.     }
124.  
125.     void SpawnImmediate()//two objects to avoid gaps between objects
126.     {
127.         Transform t = GetPoolObject();
128.         if (t == null) return; //true means pool size is too small
129.         Vector3 pos = Vector3.zero;
130.         pos.x = (immediateSpawnPos.x * Camera.main.aspect)/targetAspect;
131.         pos.y = Random.Range(ySpawnRange.min, ySpawnRange.max);
132.         t.position = pos;
133.         Spawn();
134.     }
135.  
136.     void Shift()
137.     {
138.         for (int i = 0; i < poolObjects.Length; i++)
139.         {
140.             poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;
141.             CheckDisposeObject(poolObjects[i]); //checking if the position is less than spawn position
142.         }
143.     }
144.  
145.     void CheckDisposeObject(PoolObject poolObject)
146.     {
147.         if (poolObject.transform.position.x < ( -defaultSpawnPos.x * Camera.main.aspect)/targetAspect) //should spawn offscreen so assume negative x is out of sight so can be removed
148.         {
149.             poolObject.Dispose();
150.             poolObject.transform.position = Vector3.one * 1000; //high value the user wont see
151.         }
152.     }
153.  
154.     Transform GetPoolObject()
155.     {
156.         for (int i = 0; i < poolObjects.Length; i++)
157.         {
158.             if (!poolObjects[i].inUse)
159.             {
160.                 poolObjects[i].Use();
161.                 return poolObjects[i].transform;
162.             }
163.         }
164.         return null;
165.     }
166. }
167.  

I think I found someone with a similar issue here https://answers.unity.com/questions/51331/how-to-check-if-something-is-null.html that you are talking about, but unsure how to translate over to my code?

 

So, in your Shift() function, you'd replace:

Code (CSharp):

1. poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;

with:

Code (CSharp):

1. if (poolObjects[i] != null) {
2.     poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;
3. }

You may also need to move your CheckDispose() function if that causes an error too.

 

Yeah still getting the same error:

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Transform.get_localPosition () (at C:/buildslave/unity/build/artifacts/generated/common/runtime/TransformBindings.gen.cs:41)
Parallaxer.Shift () (at Assets/scripts/Parallaxer.cs:142)
Parallaxer.Update () (at Assets/scripts/Parallaxer.cs:88)

Code (CSharp):

1.  
2.     void Shift()
3.     {
4.         for (int i = 0; i < poolObjects.Length; i++)
5.         {
6.             if (poolObjects[i] != null)
7.             {
8.                 poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;
9.             }
10.             CheckDisposeObject(poolObjects[i]); //checking if the position is less than spawn position
11.         }
12.     }
13.  
14.     void CheckDisposeObject(PoolObject poolObject)
15.     {
16.         if (poolObject.transform.position.x < ( -defaultSpawnPos.x * Camera.main.aspect)/targetAspect) //should spawn offscreen so assume negative x is out of sight so can be removed
17.         {
18.             poolObject.Dispose();
19.             poolObject.transform.position = Vector3.one * 1000; //high value the user wont see
20.         }
21.     }
22.  

What do you mean by move the CheckDispose() function? Where to?

 

Code (CSharp):

1. void Shift()
2.     {
3.         for (int i = 0; i < poolObjects.Length; i++)
4.         {
5.             if(poolObjects[i] != null)
6.             {
7.                 poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;
8.                 CheckDisposeObject(poolObjects[i]); //checking if the position is less than spawn position
9.             }
10.            
11.         }
12.     }
13.  
14.     void CheckDisposeObject(PoolObject poolObject)
15.     {
16.         if (poolObject.transform.position.x < ( -defaultSpawnPos.x * Camera.main.aspect)/targetAspect) //should spawn offscreen so assume negative x is out of sight so can be removed
17.         {
18.             poolObject.Dispose();
19.             poolObject.transform.position = Vector3.one * 1000; //high value the user wont see
20.         }
21.     }

Either position of CheckDisposeObect in the shift function gives the same error

 

Could you post the error you get with the Check inside the if statement?

 

Error:

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Transform.get_localPosition () (at C:/buildslave/unity/build/artifacts/generated/common/runtime/TransformBindings.gen.cs:41)
Parallaxer.Shift () (at Assets/scripts/Parallaxer.cs:142)
Parallaxer.Update () (at Assets/scripts/Parallaxer.cs:88)


Code:

Code (CSharp):

1.  
2.     void Shift()
3.     {
4.         for (int i = 0; i < poolObjects.Length; i++)
5.         {
6.             if (poolObjects[i] != null)
7.             {
8.                 poolObjects[i].transform.localPosition += -Vector3.right * shiftSpeed * Time.deltaTime;
9.                 CheckDisposeObject(poolObjects[i]); //checking if the position is less than spawn position
10.             }
11.  
12.         }
13.     }
14.  
15.     void CheckDisposeObject(PoolObject poolObject)
16.     {
17.         if (poolObject.transform.position.x < ( -defaultSpawnPos.x * Camera.main.aspect)/targetAspect) //should spawn offscreen so assume negative x is out of sight so can be removed
18.         {
19.             poolObject.Dispose();
20.             poolObject.transform.position = Vector3.one * 1000; //high value the user wont see
21.         }
22.     }
23.  

 

Ah, okay. So the destroy operation didn't remove the entire GameObject, only its Transform. So if you null check, you'll have to be more specific and do:

Code (CSharp):

1. if (poolObjects[i].transform != null) { }

 

Great so now the collectible disappears as intended and points are still awarded, however its now made in even larger error when game over occurs. E.g. when the user dies, they are presented with the game over screen and you click the menu button at the bottom to return to the menu, this now breaks everything:

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Transform.set_position (Vector3 value) (at C:/buildslave/unity/build/artifacts/generated/common/runtime/TransformBindings.gen.cs:28)
Parallaxer.GameOverConfirmed () (at Assets/scripts/Parallaxer.cs:75)
GameManager.ConfirmGameOver () (at Assets/scripts/GameManager.cs:168)
UnityEngine.Events.InvokableCall.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:165)
UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:58)
UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update()

 

You still have something trying to access the destroyed objects. Seems to be in the parallax script again. You're going to want to remove the null entries from the list. One way to do it, since you're already looping through all the objects, is to mark each null index, then delete them all once the loop finishes.

However, as long as you're deleting your objects from outside of the parallax script, you're going to have to keep manually syncing the data, so if you change something after fixing the issue, it might come back.

If you're going to continue with the strategy of the parallax script controlling coin movement, then you could have the coins mark themselves to-be-deleted, which the parallax script would pick up later, or they could ask the parallax script directly to remove them from the list. Something like:

Code (CSharp):

1. public class Coin : MonoBehaviour {
2.     private ParallaxController controller;
3.     public ParallaxController Controller { private get; set; }
4.    
5.     private void OnCollide(Collider other) { // This line probably not accurate
6.         controller.GetRidOf(this);
7.     }
8. }

Then the parallax script would give each spawned coin a reference to itself. Thus your config method would become this:

Code (CSharp):

1. void Configure()
2.     {
3.         targetAspect = targetAspectRatio.x / targetAspectRatio.y;
4.         poolObjects = new PoolObject[poolSize];
5.         for (int i = 0; i < poolObjects.Length; i++)
6.         {
7.             GameObject go = Instantiate(Prefab) as GameObject;
8.             Transform t = go.transform;
9.             t.SetParent(transform); //has the parent of object script is linked to
10.             t.position = Vector3.one * 1000; //offscreen again to avoid user seeing it
11.             poolObjects[i] = new PoolObject(t);
12.            
13.             // NEW STUFF
14.             t.GetComponent<Coin>().Controller = this;
15.         }
16.         if (spawnImmediate)
17.         {
18.             SpawnImmediate();
19.         }
20.     }

Lastly, you'd add that GetRidOf() method in the parallax script which finds the object in the pool and removes it. You currently have a fixed size array, so that might be a bit of a finicky operation. You may want to consider implementing your pool with a typed List<>, since you're iterating in order and removing from the middle.

 

Was this post ever resolved? I am having the same issue with my parallax script, once I collect the coins

 

Not Sure if this was ever resolved but I kinda figuered it out with trying all the above stuff as per trial and error, and finally got to where you guys are right now.Soif You got stuck like me
like at this below point ...

instead of doing the (GetRidOf) part which (CDMcGwire) suggested...not that he was wrong. he just gave an alternate approach and it tested out fine .... but if you guys get stuck at this part where you get the bellow errors.

That just means that when you hit the replay button and the bellow error popsup...

i guess we are all following the flappy bird project. so weshould all have the same files...and functions..

On replay you will get the big chunk of errors.which just means that the

the replay button calls(ConfirmeGameOver() function) which intern calls the (OnGameOverConfirmed()) which is in the Paralaxer script.

just replace that with
void OnGameOverConfirmed()
{
for (int i = 0; i < poolObjects.Length; i++)
{
if (poolObjects.transform != null) // call the null check function on this line and everything should be fine
{
poolObjects.Dispose();//
poolObjects.transform.position = UnityEngine.Vector3.one * 1000;//
}
}//
if (spawnImmediate)
{
SpawnImmediate();//
}//
}//

the entire big chunk of error dissapears...
Hope it helps the next person that jumps to this page in the future....

Happy flappybird to you too...
Took me a long time to figure it out since Visual studioc doesnt let me debug unity projects on the go... wish they could find a way to let us debug all the codes via VS things would have been easier to find.

But what the hell...
old school (Trial and Error) is the best way.
Just saved 3 hours of your time, hope you guys pay it forward 3 folds.

this officially ends the unsolved mystery