EditorWindow.focusedWindowChanged

Description

Called whenever the focused editor window is changed.

using UnityEditor;
using UnityEngine;

public class FocusedWindowTracker : EditorWindow
{
    [MenuItem("Window/Focused Window Tracker")]
    private static void ShowTracker() => GetWindow<FocusedWindowTracker>();

    private void OnGUI() => GUILayout.Label("I'm logging every focused window");

    private void OnEnable()
    {
        EditorWindow.focusedWindowChanged += TrackFocusedWindow;
    }

    private void OnDisable()
    {
        EditorWindow.focusedWindowChanged -= TrackFocusedWindow;
    }

    private static void TrackFocusedWindow()
    {
        Debug.Log($"Current focused window is {focusedWindow.titleContent.text}.");
    }
}