Question GetComponent() in script no longer returning a value, how do I work out what is going wrong?

After saving and commiting to my repo, all of the getcomponents in my script have just stopped working. One of them I fixed after just multiple recompiles but another one just refuses to work.

Code (CSharp):

1. public abstract class BaseBar : MonoBehaviour
2. {
3.     [HideInInspector] public Slider slider;
4.     [HideInInspector] public Player.Player player;
5.  
6.     private TextMeshProUGUI text;
7.  
8.     private void Start()
9.     {
10.         this.slider = GetComponent<Slider>();
11.         this.text = gameObject.transform.Find("ValueText").GetComponent<TextMeshProUGUI>();
12.         this.player = GameObject.FindWithTag("Player").GetComponent<Player.Player>();
13.     }
14.  
15.     public virtual void SetMaxValue(int value)
16.     {
17.         this.slider.maxValue = value;
18.         this.slider.value = value;
19.     }
20.  
21.     public void SetValue(int value)
22.     {
23.         this.slider.value = value;
24.     }
25.  
26.     public void SetTextValues(int current, int max)
27.     {
28.         this.text.text = current.ToString() + "/" + max.ToString();
29.     }
30. }
31.  

However this still causes:

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. BaseBar.SetTextValues (System.Int32 current, System.Int32 max) (at Assets/Scripts/UI/Hud/BaseBar.cs:32)
3. HpBar.SetInitialValues (System.Int32 maxHp, System.Int32 hp) (at Assets/Scripts/UI/Hud/HpBar.cs:12)
4. Player.Player.Start () (at Assets/Scripts/Player/Player.cs:31)
5.  

I don't understand how this is even happening as I've verified that these are the correct paths to getting the components. However saving the scene and commiting has just broke this.

 

1. Try to avoid .Find, as it's very inaccurate and prone to make bugs.
2. Debug everything, log the .Find stuff as well to see how that does

 

What would be the alternative to .Find?

 

Typically you would either hard link references in the editor or use/create a more robust dependency injection system that is more reliable and more performant.

Either way in this situation as DevDunk said you should use the debugger to find out precisely what is happening. More than likely the values assigned in Start are invalid because they didn't find what was needed. Perhaps the objects are missing from the scene? Or the tags are wrong? Or the hierarchy has been changed and your code isn't robust enough to work around that.

 

There are multiple alternatives: (i) direct assignment through the Inspector, (ii) static field referencing the instance of the object, (iii) a service locator, etc. Here's an example of a static field.

Add a static field to Player:

Code (csharp):

1. public static Player Instance;

Assign it in Awake():

Code (csharp):

1. Instance = this;

Access it in Start() from BaseBar:

Code (csharp):

1. this.player = Player.Player.Instance;

 

Keep in mind that using GetComponent<T>() and its kin (in Children, in Parent, plural, etc) to try and tease out Components at runtime is definitely deep into super-duper-uber-crazy-Ninja advanced stuff.

This sort of coding is to be avoided at all costs unless you know exactly what you are doing.

If you run into an issue with any of these calls, start with the documentation to understand why.

There is a clear set of extremely-well-defined conditions required for each of these calls to work, as well as definitions of what will and will not be returned.

In the case of collections of Components, the order will NEVER be guaranteed, even if you happen to notice it is always in a particular order on your machine.

It is ALWAYS better to go The Unity Way(tm) and make dedicated public fields and drag in the references you want.

Remember the first rule of GameObject.Find():

Do not use GameObject.Find();

More information: https://starmanta.gitbooks.io/unitytipsredux/content/first-question.html

More information: https://forum.unity.com/threads/why-cant-i-find-the-other-objects.1360192/#post-8581066

In general, DO NOT use Find-like or GetComponent/AddComponent-like methods unless there truly is no other way, eg, dynamic runtime discovery of arbitrary objects. These mechanisms are for extremely-advanced use ONLY.

If something is built into your scene or prefab, make a script and drag the reference(s) in. That will let you experience the highest rate of The Unity Way(tm) success of accessing things in your game.