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Asked: 2025-04-19T02:14:00+05:30

Why is InputManagerScript.Instance null during PlayerLocomotionInput’s OnEnable cycle, causing a NullReferenceException in Unity?

I’m hitting a frustrating wall with my Unity project and could really use some insights. I’ve been working on a 3D game with a third-person perspective, and initially, everything was going smoothly when I implemented my character controller with an ActionMap for basic movements like walking, sprinting, and jumping. That part was seamless.

However, things took a turn for the worse when I decided to create a separate ActionMap for other interactions like attacking, gathering, and interacting with objects. I thought centralizing the input management in a single script called `InputManagerScript` would make my life easier. My plan was to set it up as a singleton so that I could access the `PlayerControls` object from anywhere.

Here’s where the trouble starts. As soon as I hit play mode, I get this annoying `NullReferenceException` in the `OnEnable` method of my `PlayerLocomotionInput` script. After doing a little debugging, I discovered that `InputManagerScript.Instance` is null when `PlayerLocomotionInput`’s `OnEnable` is called. So, I’m left scratching my head because I expected the singleton to be initialized by then!

I noticed that the `DontDestroyOnLoad` object I expected to see in the hierarchy during play mode isn’t showing up either. I double-checked my `Awake` method in `InputManagerScript`, and it seems fine, but clearly, something is off.

Here’s a snippet of the relevant part of `InputManagerScript`:

“`csharp
private void Awake()
{
if (Instance != null && Instance != this)
{
Destroy(this.gameObject);
return;
}
else
{
Instance = this;
DontDestroyOnLoad(gameObject);
}
}
“`

And in `PlayerLocomotionInput`:

“`csharp
private void OnEnable()
{
InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.Enable();
InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.SetCallbacks(this);
}
“`

I’m just wondering if anyone can help me figure out why `Instance` is null during the execution of `PlayerLocomotionInput`’s `OnEnable`. Am I missing something in the order of operations, or could it be something else entirely? Your thoughts would be super appreciated!

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    2 Answers

    1. The core issue here stems from the script execution order in Unity and the lifecycle methods involved. Unity does not guarantee a specific order for the invocation of Awake, OnEnable, and Start methods across different scripts unless explicitly specified. In your case, the singleton instance of the InputManagerScript is being assigned in its Awake() method, yet PlayerLocomotionInput relies on it in its own OnEnable(). If PlayerLocomotionInput is enabled before InputManagerScript‘s Awake() has executed, you’ll encounter a NullReferenceException as the singleton has not yet been initialized. Additionally, double-check if you’re correctly instantiating and attaching this singleton script to a GameObject that’s active in your initial scene– absence of a DontDestroyOnLoad object in the hierarchy typically indicates it hasn’t been successfully instantiated or marked accordingly.

      To resolve your issue, explicitly set the script execution order in Unity (via Project Settings → Script Execution Order), ensuring InputManagerScript is executed before any scripts relying on its instance. Alternatively, move singleton-dependent logic from OnEnable() to the Start() method instead, because by the time Start() runs, all Awake and OnEnable methods across scripts are guaranteed to have completed. This change ensures InputManagerScript.Instance will be properly initialized and accessible, eliminating your NullReferenceException issue.

    2. It sounds like you’re running into a classic issue with Unity’s execution order! When you’re dealing with singletons like `InputManagerScript`, the timing of when they are created and when other scripts try to access them is super important.

      From what you’ve described, it looks like `PlayerLocomotionInput`’s `OnEnable` method is being called before `InputManagerScript`’s `Awake` method finishes setting up the singleton. This can happen if the `PlayerLocomotionInput` component is attached to an object that initializes earlier in the hierarchy compared to `InputManagerScript`.

      A couple of things to try:

      • Check Execution Order: You can set the script execution order in Unity. Try moving `InputManagerScript` higher than `PlayerLocomotionInput` so that the singleton initializes first.
      • Debug Logs: Add some `Debug.Log()` statements in both `Awake()` and `OnEnable()` to better trace when each is being called. This could give you more insight into the order they’re being executed.
      • DontDestroyOnLoad Check: Make sure that `InputManagerScript` truly is being instantiated and that other scripts aren’t accidentally destroying it elsewhere.

      The whole singleton pattern can be pretty tricky if you’re new to it, especially regarding the order of initializations. But once you get the hang of it, it makes management a lot easier!

      Hope that helps you debug your game!