Question NullReferenceException: Object reference not set to an instance of an object

Hi, I'm new to unity and trying to create a health system in a game I am making. But I keep getting this error:
NullReferenceException: Object reference not set to an instance of an object

This is the script for changing the Health Bar and it says the error message is on the line, Healthslider.value = health:

Code (CSharp):

1. public class HealthBarScript : MonoBehaviour
2. {
3.     public Slider HealthSlider;
4.     public UnitHealth _playerHealth = new UnitHealth(100, 100);
5.  
6.  
7.     private void start()
8.     {
9.         HealthSlider = GetComponent<Slider>();
10.     }
11.  
12.     public void SetHealth(int Health)
13.     {
14.         HealthSlider.value = Health;
15.     }
16.     public void SetMaxHealth(int maxHealth)
17.     {
18.         HealthSlider.maxValue = maxHealth;
19.         HealthSlider.value = maxHealth;
20.     }
21.  
22. }

This is the script I am calling the function from:

Code (CSharp):

1. public class playerBehavouir : MonoBehaviour
2. {
3.     [SerializeField] HealthBarScript healthbar;
4.     public UnitHealth _playerHealth = new UnitHealth(100, 100);
5.     public int test;
6.  
7.     void Start()
8.     {
9.         healthbar.SetMaxHealth(GameManager.gameManager._playerHealth.MaxHealth);
10.     }
11.  
12.     void Update()
13.     {
14.         if(Input.GetKeyDown(KeyCode.G))
15.         {
16.             PlayerTakeDamage(20);
17.             Debug.Log(GameManager.gameManager._playerHealth.Health);
18.         }
19.         if (Input.GetKeyDown(KeyCode.F))
20.         {
21.             PlayerHeal(10);
22.             Debug.Log(GameManager.gameManager._playerHealth.Health);
23.         }
24.     }
25.  
26.     private void PlayerTakeDamage(int Damage)
27.     {
28.         GameManager.gameManager._playerHealth.DamageUnit(Damage);
29.         healthbar.SetHealth(GameManager.gameManager._playerHealth.Health);
30.     }
31.     private void PlayerHeal(int Healing)
32.     {
33.         GameManager.gameManager._playerHealth.HealUnit(Healing);
34.         healthbar.SetHealth(GameManager.gameManager._playerHealth.Health);
35.     }
36. }

 

simple typo line 7. Code is very picky about case-sensitive stuff. So the compiler see's your void of

start()

as your own created method, rather than Unity's built in method of

Start()

 

Thank you for pointing that out, I still get the same error though

 

The answer is always the same... ALWAYS!

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Three steps to success:
- Identify what is null <-- any other action taken before this step is WASTED TIME
- Identify why it is null
- Fix that

 

I'd say another typo issue, line 3, 9, 14, 18, 19. As in line 3 that should be a lower case name, so you never get confused on what is a full class, versus some variable you declared at the top of the script. But to be honest, it should still work.

So since it's a public reference, can you not just put it in the proper slot, in the Inspector? And do away with trying to get it's component, since it already would have it?

But if you want to get it's component through script, you need to define it's path, and on which object it's on. Unless "Slider" is a component itself, on said object with the same script your using(which I don't think it is).