Unity Editor Input example using the New Input System

EditorInputCapture.cs

using UnityEditor;
using UnityEngine;
#if ENABLE_INPUT_SYSTEM
using UnityEngine.InputSystem;
#endif

//Simple Editor-side New Input System capture
namespace Invertex.UnityEditor.InputTools
{
    [InitializeOnLoad]
    static class EditorInputCapture
    {
#if ENABLE_INPUT_SYSTEM
        private readonly static EditorInputButton keyP;
        readonly static EditorInputButton gamepadStartBtn;

        private static void EditorUpdate()
        {
            keyP.Update();
            gamepadStartBtn.Update();
        }

        static EditorInputCapture()
        {
            keyP = new EditorInputButton("<Keyboard>/p");
            keyP.OnPressDown += () => { Debug.Log("P Pressed!"); };
            keyP.OnPressUp += () => { Debug.Log("P Depressed!"); };
            keyP.OnPressHeld += () => { Debug.Log("P Held!"); };

            gamepadStartBtn = new EditorInputButton("<Gamepad>/start");
            gamepadStartBtn.OnPressDown += () => { 
                Debug.Log("Start Pressed!");
                EditorApplication.isPlaying = !EditorApplication.isPlaying;
            };
            gamepadStartBtn.OnPressUp += () => { Debug.Log("Start Depressed!"); };
            gamepadStartBtn.OnPressHeld += () => { Debug.Log("Start Held!"); };

            EditorApplication.update += EditorUpdate; //Could also just assign the key.Update() here if you don't need to process keys in a certain order.
        }

        private class EditorInputButton
        {
            private readonly InputControl button;

            public bool PressDown { get; private set; }
            public bool PressHeld { get; private set; }
            public bool PressUp { get; private set; }

            public delegate void PressAction();
            public PressAction OnPressDown;
            public PressAction OnPressHeld;
            public PressAction OnPressUp;

            public void Update()
            {
                if (button != null && button.device.enabled)
                {
                    bool pressed = button.IsPressed();
                    if (pressed)
                    {
                        if (!PressHeld)
                        {
                            PressDown = PressHeld = true;
                            OnPressDown?.Invoke();
                        }
                        else
                        {
                            PressDown = false;
                            OnPressHeld?.Invoke();
                        }
                    }
                    else if (PressHeld)
                    {
                        PressHeld = false;
                        PressUp = true;
                        OnPressUp?.Invoke();
                    }
                    else { PressUp = false; }
                }
            }

            public EditorInputButton(string controlPath)
            {
                button = InputSystem.FindControl(controlPath);
                if (button == null) { Debug.LogWarning("Couldn't find button mapping: " + controlPath + "\n Device may not be connected."); }
            }
        }
    }
#endif
}