koobas.hobune.stream
Why is my component coming back as null?
I'm trying to update a variable from one script in another and was initially getting the error
NullReferenceException: Object reference not set to an instance of an object GameController+<asteroidWaves>c__Iterator2.MoveNext () (at Assets/Scripts/GameController.cs:51)
Line 51 is asteroid.increaseSpeed(speed);
When I did a check to make sure that it is indeed null, I'm being told that it is. Why am I returning null on AsteroidMover and how do I fix it?
public class GameController:MonoBehaviour{
public GameObject hazard;
public Vector3 hazard_values;
public int min_asteroids;
public int max_asteroids;
private int hazard_count;
public float spawn_wait;
public float start_wait;
public float wave_wait;
private int wave_count = 0;
public Text score_text;
private int score;
public Text restart;
public Text game_over_text;
private bool game_over;
private bool new_game;
private AsteroidMover asteroid;
void Start(){
game_over = false;
new_game = false;
restart.text = "";
game_over_text.text = "";
score = 0;
updateScore();
StartCoroutine(asteroidWaves());
}
void Update(){
if(new_game){
if(Input.GetKeyDown(KeyCode.Return)){
Application.LoadLevel(Application.loadedLevel);
}
}
}
IEnumerator asteroidWaves(){
yield return new WaitForSeconds(start_wait);
while(true){
asteroid = GetComponent<AsteroidMover>();
wave_count += 1;
if(asteroid != null){
if(wave_count > 1){
min_asteroids *= wave_count;
max_asteroids += min_asteroids;
asteroid.increaseSpeed();
}
}
else{
Debug.Log ("Asteroid is null");
}
hazard_count = Random.Range(min_asteroids, max_asteroids);
for(int i = 0; i < hazard_count; i++){
Vector3 hazard_position = new Vector3(Random.Range(-hazard_values.x, hazard_values.x), hazard_values.y, hazard_values.z);
Quaternion hazard_rotation = Quaternion.identity;
Instantiate(hazard, hazard_position, hazard_rotation);
yield return new WaitForSeconds(spawn_wait);
}
yield return new WaitForSeconds(wave_wait);
}
}
}
public class AsteroidMover:MonoBehaviour{
private Rigidbody asteroid;
public float speed;
void Start(){
asteroid = GetComponent<Rigidbody>();
asteroid.velocity = transform.forward * speed;
}
public void increaseSpeed(){
speed += 0.5f;
Debug.Log (speed);
}
}
I suspect it is because you only set 'asteroid' in the Start function of GameController, however your logic is:
if(asteroid != null)
{
asteroid = FindObjectOfType<AsteroidMover> ();
}
So that says "if my asteroid is not null, find an asteroid"
So if your asteroid is already null, you will never attempt to find an asteroid.
Presumably that's a typo, and should read:
if(asteroid == null)
{
asteroid = FindObjectOfType<AsteroidMover> ();
}
Although unless you intend to set 'asteroid' in the inspector, the 'if statement' is probably redundant, as you always want to find your asteroid in the Start function, so it could probably just be:
asteroid = FindObjectOfType<AsteroidMover> ();
Hope that helps
-Chris
Ok, so if I just get rid of the if statement, asteroid should never return null?
Assu$$anonymous$$g there is an object in the world with an 'Asteroid$$anonymous$$over' component attached to it, yes!
If you don't have an 'Asteroid$$anonymous$$over' in your scene, then it won't find one.
Give it a try :)
-Chris
I have the Asteroid$$anonymous$$over script attached to a prefab that gets instantiated when the game starts.
No problem - we all have to learn :)
FindObjectOfType simply searches the scene for a GameObject that contains a component of type Asteroid$$anonymous$$over.
If one doesn't exist, it will return null.
If you are waiting until the game actually runs before Instantiating them, then you would need to make sure you didn't look for it until they had been instantiated. I don't know enough about your code to know if that'll be the case, but if GameController exists when the scene starts up, then you'll be relying on the asteroids being instantiated before 'Start' is called on it, which is probably optimisitic.
You could try fiddling with script priorities, but the simplest approach is probably just to find it when you need it:
IEnumerator asteroidWaves()
{
yield return new WaitForSeconds(start_wait);
while(true)
{
wave_count += 1;
//just locally find our asteroid here before we use it
//NOTE: we can now get rid of the member variable called 'asteroid'
Asteroid$$anonymous$$over asteroid = FindObjectOfType<Asteroid$$anonymous$$over> ();
if(asteroid != null)
{
if(wave_count > 1)
{
$$anonymous$$_asteroids *= wave_count;
max_asteroids += $$anonymous$$_asteroids;
asteroid.increaseSpeed(speed);
}
}
hazard_count = Random.Range($$anonymous$$_asteroids, max_asteroids);
for(int i = 0; i < hazard_count; i++)
{
Vector3 hazard_position = new Vector3(Random.Range(-hazard_values.x, hazard_values.x), hazard_values.y, hazard_values.z);
Quaternion hazard_rotation = Quaternion.identity;
Instantiate(hazard, hazard_position, hazard_rotation);
yield return new WaitForSeconds(spawn_wait);
}
yield return new WaitForSeconds(wave_wait);
if(game_over)
{
restart.text = "Press 'Enter' to start a new game.";
new_game = true;
break;
}
}
}
So, I implemented this and asteroid is still returning as null.
