[C#]特定のプロセスのコントロールのフォーカス変更を監視する

main.cs

using System;
using System.Diagnostics;
using System.Threading;
using System.Windows.Automation;

namespace ConsoleApplication1
{
    class Program
    {
        static AutomationFocusChangedEventHandler focusHandler = null;
        private static int processId;

        static void Main(string[] args)
        {
            // 監視するプロセス
            string processPath = @"WindowsFormsApplication1";

            Process process = Process.Start(processPath);

            Thread.Sleep(1000);
            processId = process.Id;

            try
            {
                SubscribeToFocusChange();
                Console.WriteLine("App Start");
                Console.ReadKey();
            }
            finally
            {
                UnsubscribeFocusChange();
                Console.WriteLine("App Close");
            }
        }

        /// <summary>
        /// Create an event handler and register it.
        /// </summary>
        public static void SubscribeToFocusChange()
        {
            focusHandler = new AutomationFocusChangedEventHandler(OnFocusChange);
            Automation.AddAutomationFocusChangedEventHandler(focusHandler);
        }

        /// <summary>
        /// Handle the event.
        /// </summary>
        private static void OnFocusChange(object src, AutomationFocusChangedEventArgs e)
        {
            if (src is AutomationElement)
            {
                var target = src as AutomationElement;
                if (target.Current.ProcessId == processId)
                {
                    if (string.IsNullOrEmpty(AutomationElement.FocusedElement.Current.Name))
                        Console.WriteLine("OnFocusChange?:{0}", AutomationElement.FocusedElement.Current.ClassName);
                    else
                        Console.WriteLine("OnFocusChange:{0}({1})", AutomationElement.FocusedElement.Current.Name, AutomationElement.FocusedElement.Current.ClassName);
                }
            }
        }

        /// <summary>
        /// Cancel subscription to the event.
        /// </summary>
        public static void UnsubscribeFocusChange()
        {
            if (focusHandler != null)
            {
                Automation.RemoveAutomationFocusChangedEventHandler(focusHandler);
            }
        }

    }
}