A class to monitor when a WinForm form is found

WinFormMonitor.cs

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace WindowsFormsApp11
{
    public class WinFormMonitor : IDisposable
    {
        private readonly IntPtr _eventHook;
        private readonly IList<int> _detectedFormHashes = new List<int>();

        public event EventHandler<Form> NewFormCreated = (sender, form) => { };

        public WinFormMonitor()
        {
            _eventHook = SetWinEventHook(
                EVENT_OBJECT_CREATE,
                EVENT_OBJECT_CREATE,
                IntPtr.Zero,
                WinEventProc,
                0,
                0,
                WINEVENT_OUTOFCONTEXT);
        }

        public void Dispose()
        {
            _detectedFormHashes.Clear();
            UnhookWinEvent(_eventHook);
        }

        private void WinEventProc(IntPtr hWinEventHook, uint eventType,
            IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
        {
            // filter out non-HWND namechanges... (eg. items within a listbox)
            if (idObject != 0 || idChild != 0) return;
            if (!TryFindForm(hwnd, out var foundForm)) return;

            RaiseIfNewFormFound(foundForm);
        }

        private void RaiseIfNewFormFound(Form foundForm)
        {
            var formHash = foundForm.GetHashCode();
            if (_detectedFormHashes.Contains(formHash)) return;

            NewFormCreated(this, foundForm);
            _detectedFormHashes.Add(formHash);
        }

        private static bool TryFindForm(IntPtr handle, out Form foundForm)
        {
            foreach (Form openForm in Application.OpenForms)
            {
                if (openForm.Handle != handle) continue;
                foundForm = openForm;
                return true;
            }
            
            foundForm = null;
            return false;
        }

        private const uint EVENT_OBJECT_CREATE = 0x8000;
        private const uint WINEVENT_OUTOFCONTEXT = 0;

        private delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType,
            IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime);

        [DllImport("user32.dll")]
        private static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr
                hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess,
            uint idThread, uint dwFlags);

        [DllImport("user32.dll")]
        private static extern bool UnhookWinEvent(IntPtr hWinEventHook);
    }
}