Develop Reference

Unity - What is OOP - Null Reference Exception

im kind of newbie to unity and object oriented programming. Recently im trying to clone Cube Surfer mobile game. Basic idea from my view is this ;
-When we triggered to collactable cubes which consist script will be duplicated and it will be belong the main cube parent as child object then triggered cube will be destroyed.(After positioning)
-Later this duplicate child objects(cubes) will do the same when they enter trigger area of other collectable cubes(those will be the same prefab but did not yet create a prefab)
Im trying to collect(create a clone of it position and destroy the object) cubes. For first cube, I added some code to my movement script which is below.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class Movement : MonoBehaviour
{
public GameObject addup;
Rigidbody rb;
float controlSpeed = 1.25f;
float forwardMovementSpeed = 10f;
private Vector3 axisGet;
float deathTime;
public int collected;
// Start is called before the first frame update
void Start()
{
rb = gameObject.GetComponent<Rigidbody>();
collected = 0;
}
// Update is called once per frame
void FixedUpdate()
{
axisGet = new Vector3(0, 0, Input.GetAxis("Horizontal"));
rb.MovePosition(transform.position + Vector3.left * forwardMovementSpeed * Time.deltaTime + axisGet * controlSpeed * Time.deltaTime);
}
private void OnTriggerEnter(Collider other)
{
if(other.tag=="add up")
{
gameObject.transform.position += Vector3.up;
var newObject = Instantiate(addup.gameObject, Vector3.zero, Quaternion.identity);
newObject.transform.parent = transform;
newObject.transform.position = gameObject.transform.position + Vector3.down;
Destroy(other.gameObject);
newObject.GetComponent<BoxCollider>().isTrigger = false;
collected++;
}
}
}
WORKED WITHOUT ERROR BUT THEN, I applied the same method to collectable cubes scripts.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class UpNdown : MonoBehaviour
{
void Start()
{
}
// Update is called once per frame
void Update()
{
}
private void OnTriggerEnter(Collider other)
{
if (other.tag == "add up")
{
GameObject parentTransform;//?????????
parentTransform = gameObject.GetComponentInParent<GameObject>(); //get first cube component
parentTransform.transform.position += Vector3.up; //first cube one unit up
GameObject newObject; // ?????????
newObject = Instantiate(other.gameObject, Vector3.zero, Quaternion.identity) as GameObject; //???????????
Debug.Log(newObject);
var collect = parentTransform.GetComponent<Movement>().collected;
if (other != null)
{
Destroy(other.gameObject); //destroy triggered collactable
}
newObject.transform.parent = parentTransform.transform; //setting parent to new cube
newObject.transform.position = parentTransform.transform.position + Vector3.down * (collect + 1); //setting position of new cube
newObject.GetComponent<BoxCollider>().isTrigger = false; //prepare the below cubes(new cubes) for trigger with other collactable cubes
collect++;
}
}
}
And, I had nullexception error in every line in ontriggerenter method then, I changed(added) the lines with question marks. So, I get
ArgumentException: GetComponent requires that the requested component 'GameObject' derives from MonoBehaviour or Component or is an interface.
UnityEngine.GameObject.GetComponentInParent[T] (System.Boolean includeInactive) (at :0)
UnityEngine.GameObject.GetComponentInParent[T] () (at :0)
UpNdown.OnTriggerEnter (UnityEngine.Collider other)
I thought, I understood the OOP instance idea which objects in the scenes are instances scripts has their own value... but i dont understand that while I was operating on a instance why it is null in the memory :((((((((((((( if PC can't access how instantiates the object ?
SORRY I WRITE THIS LONG BUT IM ABOUT THE EDGE AGAIN I DON'T WANT TO QUIT BECAUSE OF FACING THIS PROBLEM AGAIN
TY FOR YOUR ANSWERS, ALREADY APPRECIATED :)

GameObject is no component (it is rather a container of all components attached to it!)
=> you can't get it using GetComponent or GetComponentInParent at all. (Btw Note that GetComponentInParent starts the search on this object itself first before bubling up the hierarchy so either way this isn't what you want to use).
What you want is simply transform.parent to get the Transform component of the parent object of the object this script is attached to (assuming the rest of your code does what it should)
private void OnTriggerEnter(Collider other)
{
// Rather use CompareTag instead of string ==
// The latter silently fails in case of typos making your debugging life miserabel
// it is also slightly less efficient
if (!other.CompareTag("add up")) return;
// Get the parent of this object
var parentTransform = transform.parent;
// Cache this you will need it later see below
var parentMovement = parentTransform.GetComponent<Movement>();
var collect = parentMovement.collected;
parentTransform.position += Vector3.up;
// By using the correct type you want later you can skip GetComponent
var newObjectCollider = Instantiate(other, Vector3.zero, Quaternion.identity);
Debug.Log(newObjectCollider);
Destroy(other.gameObject);
newObjectCollider.transform.parent = parentTransform;
newObjectCollider.transform.position = parentTransform.position + Vector3.down * (collect + 1);
newObjectCollider.isTrigger = false;
// This does absolutely nothing. Numeric values are passed by value and there is no connection
// between your local variable and the component you got it from
//collect++;
// you probably rather want to increase
parentMovement.collected++;
}
Or alternatively since you anyway have a specific component on your parent object you could also do
// Instead directly get this component
var parentMovement = GetComponentInParent<Movement>();
// Then wherever needed access the transform through it
var parentTransform = parentMovement.transform;
...
I'm quite sure though that the other way round it is more efficient since you already know exactly which parent you are searching the component on.
Or - and this would probably be the best option - cache that parent information once right away:
// If possible already reference this vis the Inspector
[SerializeField] private Movement parentMovement;
private Transform parentTransform;
private void Awake ()
{
if(! parentMovement) parentMovement = GetComponentInParent<Movement>();
parentTransform = parentMovement.transform;
}

Ty sir my first code was nearly the same of your first answer but didn't work again at least for error.
private Transform parentTransform;
private void Awake ()
{
if(! parentMovement) parentMovement = GetComponentInParent<Movement>();
parentTransform = parentMovement.transform;
}
But this worked, I guess the problem I need to define instances to class so they don't disappear instantly on the trigger function or direct I need to define them to class.
Anyway, thank you derHugo now need to solve different problems :D

Error "Object reference not set to an instance of an object" when dealing with prefab

I was trying to get the camera follow my player (which is instantiated from a prefab) but I keep getting the error in my camera script.
My camera script (the error is in line offset = transform.position - Game.currentPlayer.transform.position;):
public class CameraControl : MonoBehaviour
{
private Vector3 offset;
private void Awake()
{
offset = transform.position - Game.currentPlayer.transform.position;
}
void LateUpdate()
{
transform.position = Game.currentPlayer.transform.position + offset;
}
}
I set my currentPlayer variable here:
void Start()
{
GameObject newPlayer = Instantiate(player,transform.position,transform.rotation);
newPlayer.name = "Player";
currentPlayer = newPlayer;
}
If you need anymore scripts to help, just ask :)

Awake is called before Start. Actually even all Awake methods are finished before the first Start is called (also see Order of Execution for Event Functions).
Therefore the reference is not set yet in Awake.
You will have to either move it to the Start method or move the instantiation part to Awake.
In both cases it is still no warranty that the Game script will have its Start executed before the GameControl. Therefore you will still have to adjust the Script Execution Order thus that Game is always excuted before GameControl. Simply
open the Edit > Project Settings > Script Execution Order
drag&drop in the Game script before the DefaultTime block
optionally also sortr already existing items
Alternatively you could use an event system:
public class Game : MonoBehaviour
{
public static event Action OnInitilalized;
public static GameObject currentPlayer;
privtae void Start()
{
GameObject newPlayer = Instantiate(player,transform.position,transform.rotation);
newPlayer.name = "Player";
currentPlayer = newPlayer;
OnInitilalized?.Invoke();
}
}
and then in the GameControl add a callback to the OnInitialized event like
private void Awake()
{
// This makes sure the callback is added only once
Game.OnInitialized -= OnGameInitialized;
Game.OnInitialized += OnGameInitialized;
}
private void OnDestroy()
{
// always make sure to remove callbacks if no longer needed
Game.OnInitialized -= OnGameInitialized;
}
privtae void OnGameInitialized()
{
offset = transform.position - Game.currentPlayer.transform.position;
}

What is the best way to pass a List from a class and use it in other scripts? [duplicate]

I've searched around and I just can't get this to work. I think I just don't know the proper syntax, or just doesn't quite grasp the context.
I have a BombDrop script that holds a public int. I got this to work with public static, but Someone said that that is a really bad programming habit and that I should learn encapsulation. Here is what I wrote:
BombDrop script:
<!-- language: c# -->
public class BombDrop : MonoBehaviour {
public GameObject BombPrefab;
//Bombs that the player can drop
public int maxBombs = 1;
// Update is called once per frame
void Update () {
if (Input.GetKeyDown(KeyCode.Space)){
if(maxBombs > 0){
DropBomb();
//telling in console current bombs
Debug.Log("maxBombs = " + maxBombs);
}
}
}
void DropBomb(){
// remove one bomb from the current maxBombs
maxBombs -= 1;
// spawn bomb prefab
Vector2 pos = transform.position;
pos.x = Mathf.Round(pos.x);
pos.y = Mathf.Round(pos.y);
Instantiate(BombPrefab, pos, Quaternion.identity);
}
}
So I want the Bomb script that's attached to the prefabgameobject Bombprefab to access the maxBombs integer in BombDrop, so that when the bomb is destroyed it adds + one to maxBombs in BombDrop.
And this is the Bomb script that needs the reference.
public class Bomb : MonoBehaviour {
// Time after which the bomb explodes
float time = 3.0f;
// Explosion Prefab
public GameObject explosion;
BoxCollider2D collider;
private BombDrop BombDropScript;
void Awake (){
BombDropScript = GetComponent<BombDrop> ();
}
void Start () {
collider = gameObject.GetComponent<BoxCollider2D> ();
// Call the Explode function after a few seconds
Invoke("Explode", time);
}
void OnTriggerExit2D(Collider2D other){
collider.isTrigger = false;
}
void Explode() {
// Remove Bomb from game
Destroy(gameObject);
// When bomb is destroyed add 1 to the max
// number of bombs you can drop simultaneously .
BombDropScript.maxBombs += 1;
// Spawn Explosion
Instantiate(explosion,
transform.position,
Quaternion.identity);
In the documentation it says that it should be something like
BombDropScript = otherGameObject.GetComponent<BombDrop>();
But that doesn't work. Maybe I just don't understand the syntax here. Is it suppose to say otherGameObject? Cause that doesn't do anything. I still get the error : "Object reference not set do an instance of an object" on my BombDropScript.maxBombs down in the explode()

You need to find the GameObject that contains the script Component that you plan to get a reference to. Make sure the GameObject is already in the scene, or Find will return null.
GameObject g = GameObject.Find("GameObject Name");
Then you can grab the script:
BombDrop bScript = g.GetComponent<BombDrop>();
Then you can access the variables and functions of the Script.
bScript.foo();
I just realized that I answered a very similar question the other day, check here:
Don't know how to get enemy's health
I'll expand a bit on your question since I already answered it.
What your code is doing is saying "Look within my GameObject for a BombDropScript, most of the time the script won't be attached to the same GameObject.
Also use a setter and getter for maxBombs.
public class BombDrop : MonoBehaviour
{
public void setMaxBombs(int amount)
{
maxBombs += amount;
}
public int getMaxBombs()
{
return maxBombs;
}
}

use it in start instead of awake and dont use Destroy(gameObject); you are destroying your game Object then you want something from it
void Start () {
BombDropScript =gameObject.GetComponent<BombDrop> ();
collider = gameObject.GetComponent<BoxCollider2D> ();
// Call the Explode function after a few seconds
Invoke("Explode", time);
}
void Explode() {
//..
//..
//at last
Destroy(gameObject);
}
if you want to access a script in another gameObject you should assign the game object via inspector and access it like that
public gameObject another;
void Start () {
BombDropScript =another.GetComponent<BombDrop> ();
}

Can Use this :
entBombDropScript.maxBombs += 1;
Before :
Destroy(gameObject);
I just want to say that you can increase the maxBombs value before Destroying the game object. it is necessary because, if you destroy game object first and then increases the value so at that time the reference of your script BombDropScript will be gone and you can not modify the value's in it.

Delete spawning list objects consistently

Already 2 days I'm trying to solve this problem but I can't.I'm trying to delete the unlimited spawning barriers consistently when they are collide with the boundary.The barriers are made from 5 cubes.Any ideas?
public List<GameObject> spawning=new List<GameObject>();
public Vector3[] positions = new Vector3[5];
public GameObject barrier;
public GameObject boundary;
void Start()
{
StartCoroutine (SpawnBarrier());
}
void Update()
{
if(true)
{
foreach (GameObject move in spawning)
move.transform.Translate (0f, 0f, -0.1f);
}
}
IEnumerator SpawnBarrier(){
yield return new WaitForSeconds (3f);
while (true) {
for(int i=0;i<=4;i++)
{
spawning.Add (Instantiate (barrier, positions [i], Quaternion.identity)as GameObject);
}
yield return new WaitForSeconds (3f);
}
}

Your barriers are marked as isTrigger on their colliders therefore you can use OnTriggerEnter to detect when any of the barriers collides with the boundary.
You need to create new script, lets call that BoundaryDetector and attach it to the barrier prefab so that every instance of the barrier will have this script attached to it.
When OnTriggerEnter is called, check if the trigger is made by the boundary. This can be done by checking for the "Player" tag since boundary is tagged as Player in your screenshot. If the detected trigger tag is "Player", first remove the spawning from the spawning List then Destroy it.
The BoundaryDetector script is as below (Must be attached to the barrier prefab):
ScriptFromYourQuestion yourInstancingSript;
void Start()
{
GameObject obj = GameObject.Find("NameOfObjectScriptInYourQuestionIsAttachedTo");
yourInstancingSript = obj.GetComponent<ScriptFromYourQuestion>();
}
void OnTriggerEnter(Collider other)
{
//Detect if we collided with the boundary
if (other.CompareTag("Player"))
{
//Remove Self/barrier from the List
yourInstancingSript.spawning.Remove(this.gameObject);
//Delete Self/barrier
Destroy(this.gameObject);
}
}
Note: The ScriptFromYourQuestion should be replaced with the name of the script in your question.
MUST DO:
To get the code above working, the following changes must be made in the Update function of the script from your question:
1.You must attach Rigidbody to at-least one of the Objects (boundary or barrier). In this case, I suggest you do so to the barrier prefab.
2.You must remove move.transform.Translate (0f, 0f, -0.1f); and replace it with Rigidbody.MovePosition and use that to move your barries because you have now attached Rigidbody to your barries and this is the proper way to move a Rigidbody Object.
Maybe something like this:
Your Update function in the code form your quesion should looks something like this:
public float speed = 100.0f;
void Update()
{
if (true)
{
foreach (GameObject move in spawning)
{
//Get Rigidbody component
Rigidbody rb = move.GetComponent<Rigidbody>();
//Calculate Z-axis pos to move to
Vector3 pos = new Vector3(0, 0, 1);
pos = pos.normalized * speed * Time.deltaTime;
//Move with Rigidbody
rb.MovePosition(rb.transform.position + pos);
}
}
}

Your problem is that you have an infinite loop while true that you're not breaking out of. Instead you should add a counter. You haven't explained what you want to do but my example is that it will breakout once it completes 10 instantiations of 5 blocks.
IEnumerator SpawnBarrier(){
spawnCount=0
yield return new WaitForSeconds (3f);
while (true) {
for(int i=0;i<=4;i++)
{
spawning.Add (Instantiate (barrier, positions [i], Quaternion.identity)as GameObject);
}
if (++spawnCount==10)
{
break;
}
yield return new WaitForSeconds (3f);
}
}

If I understood corrently, you want to destroy barriers that collided with some kind of boundary?
If the 'boundary' is the visible screen space
In this case, we can assume that, once the object is invisible to MainCamera it can be counted as out of the boundary. Keeping that in mind, we can use OnBecameInvisible() method, which is method (or message, as stated in Unity Scripting API) called by MonoBehaviour class:
// A piece of barrier that gets destroyed once out of screen
public sealed class BarrierPiece : MonoBehaviour
{
// Called once the object is no longer visible to any (scene editor included) camera
private void OnBecameInvisible()
{
Destroy(gameObject);
}
}
NOTE: if you have more than one Camera in your scene, the object must be invisible to all of the cameras in order for the OnBecameInvisible() to be called.
If the 'boundary' is other object
In this case, there are many approaches based on your game:
Create GameObject with Rigidbody component and add a script which would have OnTriggerEnter(...) method and destroy colliding barriers in it.
(Inefficient) have two static Vector2 variables, one for pivotPosition, other for maximumOffset (this one should be squared for faster calculations). Then, have script on each of the barriers and in Update() checks whether the object's squared distance to the pivotPosition is greater than maximumOffset and call Destroy(gameObject) if the condition is true.
(others) ...
Those are two that came up quickly in my mind.
Hope this helps!
EDIT
Didn't look at the images...
So for your solution, you would need to assign Rigidbody component to the Boundary and add BoxCollider component on all of the barriers. Now, create a tag, called Barrier and tag all the barriers with it. Create a script:
// Destroys barriers on collision
public sealed class BarrierBoundary : MonoBehaviour
{
// Called once the script is created
// Checks if the object has Rigidbody component attached
private void Awake()
{
Debug.Assert(GetComponent<Rigidbody>() != null);
}
private void OnCollisionEnter(Collision collision)
{
if(collision.collider.tag == "Barrier")
Destroy(collision.collider.gameObject);
}
}
(The code wasn't tested, so it can have some typos.)
Now, assign the script to the Boundary. And voila! Barriers are destroyed once hitting the boundary.
Hope (again) this helps!

How do I Transfer Instantiate put inside OnCollisionEnter() after created on another function OnCollisionExit() in Unity 3D?

I'm creating my first game "Endless Runner" and my problem is in the code, I don’t need to destroy the new object, I need to transfer them to the old place.
public class GenerateEnv1 : MonoBehaviour {
public GameObject []EnvTile;
float tileZ = 29.31f;
// Use this for initialization
void Start () {
}
// Update is called once per frame
void Update () {
}
void OnCollisionEnter (Collision col) {
if(col.gameObject.tag =="ground"){
GameObject o = Instantiate (EnvTile[Random.Range(0,4)], new Vector3(0f,0f,tileZ), Quaternion.EulerAngles(0,0,0));
tileZ += 2.96f;
}
}
void OnCollisionExit (Collision col) {
if(col.gameObject.tag =="ground"){
Destroy (col.gameObject,3); // this's i need to replace that in the new object
}
}
}

Since instantiating and destroying a tile is more costly, every time you leave a tile OnCollisionExit will fire and you will move that tile right after the next tile and so on and so forth, also instantiating two tiles onStart is enough since we're reusing them
public class GenerateEnv1 : MonoBehaviour
{
public GameObject[] EnvTile;
float tileZ = 29.31f;
// Use this for initialization
void Start()
{
Instantiate(EnvTile[Random.Range(0, 4)], new Vector3(0f, 0f, tileZ), Quaternion.EulerAngles(0, 0, 0));
Instantiate(EnvTile[Random.Range(0, 4)], new Vector3(0f, 0f, tileZ * 2), Quaternion.EulerAngles(0, 0, 0));
}
void OnCollisionExit(Collision col)
{
if (col.gameObject.tag == "ground")
{
col.gameObject.transform.position = new Vector3(col.gameObject.transform.position.x , col.gameObject.transform.position.y, col.gameObject.transform.position.z + (tileZ * 2));
}
}
}

The solution to your problem is called Object Pooling.
There's a tiny bit too little detail to provide a full code as an answer, but in general it works like that: Instantiate all the objects you'll need when the game loads, this is farily expensive and is best done at front.
Than, everything you do is do some juggling with gameObject.SetActive(true/false).
Generic implementation will contain a list of gameobjects (pool), you deactivate (instead of destroing) an object on OnCollisionExit, than you take new object from the pool (pick one that is not active), and activate it (and place it).
It is not clear however how the colliders are placed, obviously collision will not be triggered by an object that is not yet active on scene.
Is your script meant to go on the player?