architecture

[Input System] Fix FindAction NullReferenceException and Reference Breakage

Solution

input systemproject architecturedebugging

Unity 2020.3.x - Unity 6.3.x

Published Thu, Mar 26

Reviewed by _architect

Chief Editor

80 posts

Issue

A NullReferenceException is triggered within the Update loop when FindAction fails to return a valid instance. This common regression occurs after script refactoring or moving classes into a namespace, causing string-based lookups like GameObject.Find to fail silently or FindAction to mismatch with the updated Input Action Asset configuration.

Runtime crashes are mitigated by replacing fragile string-based lookups with Object.FindAnyObjectByType and validating that FindAction successfully binds to the active asset.

Explanation

Ensure the strings provided to FindAction exactly match the names defined in the active Input Action Asset editor.
Verify the InputActionMap containing the actions is enabled via Enable() before polling IsPressed() in the logic loop.
Replace name-dependent lookups with Object.FindAnyObjectByType<your game management class>() to maintain robust references regardless of hierarchy or namespace changes.
Implement null-conditional access or debug assertions in Start() to verify FindAction has correctly bound to the expected input actions.

Additional Tips

Use a generated C# class for your input asset to access actions via strongly-typed properties instead of using FindAction strings.
Check the PlayerInput component on your player object to confirm the correct asset is assigned and initialized.

Copy


using UnityEngine;
using UnityEngine.InputSystem;

namespace GamesChallenge.FlorpyBorb
{
    public class PlayerController : MonoBehaviour
    {
        private InputAction m_flapSpace;
        private InputAction m_flapMouse;
        private Rigidbody2D m_rigidbody;
        private GameManager m_gameManager;

        void Start()
        {
            // Ensure action names match the .inputactions asset exactly
            m_flapSpace = InputSystem.actions.FindAction("Jump");
            m_flapMouse = InputSystem.actions.FindAction("Flap");

            m_rigidbody = GetComponent<Rigidbody2D>();
            
            // Replace GameObject.Find with type-safe lookup
            m_gameManager = Object.FindAnyObjectByType<GameManager>();
            
            if (m_flapSpace == null) Debug.LogError("Jump action not found!");
        }

        void Update()
        {
            if (m_gameManager != null && m_gameManager.isGameRunning)
            {
                // Use null-conditional to prevent NRE if FindAction failed
                bool inputDetected = (m_flapSpace?.IsPressed() ?? false) || (m_flapMouse?.IsPressed() ?? false);
                
                if (inputDetected)
                {
                    PerformFlap();
                }
            }
        }

        private void PerformFlap()
        {
            m_rigidbody.linearVelocity = Vector2.zero;
            m_rigidbody.AddForce(Vector2.up * 5.0f, ForceMode2D.Impulse);
        }
    }
}

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[Input System] Fix FindAction NullReferenceException and Reference Breakage