Scenario

You are running a Windows Forms application that runs as a System Tray. You have a few notifications that you would like to show the user.

However, what good is notifications, if the user is on the Loo? She will not see them.

Solution

Run a timer that detects when the user is active on the machine, and then show the notification or other task you would like to provide.

Below is the sample code that will do this for you. Of course for your production environment you would use a timer of some sort or event subscription service.

I have tested this by using other applications whilst the program monitors my input and it is safe to say it works across all my applications, even when the screen is locked.

So you might want to deal with an issue where the screen is locked but the user is moving the mouse. However such an issue is an edge case that is unlikely to happen.

I know the MSDN mentions that GetLastInputInfo is not system wide, however on my Windows 10 machine, it does seem to be the case that it is system wide.

using System;
using System.Runtime.InteropServices;
using System.Timers;

namespace MyMonitor
{
    class Program
    {
        private static Timer _userActivityTimer;
        static void Main()
        {
            _userActivityTimer = new Timer(500);
            _userActivityTimer.Elapsed += OnTimerElapsed;
            _userActivityTimer.AutoReset = true;
            _userActivityTimer.Enabled = true;
            Console.WriteLine("Press the Enter key to exit the program at any time... ");
            Console.ReadLine();
        }

        private static void OnTimerElapsed(object sender, ElapsedEventArgs e)
        {
            Console.WriteLine($"Last Input: {LastInput.ToShortTimeString()}");
            Console.WriteLine($"Idle for: {IdleTime.Seconds} Seconds");
        }

        [DllImport("user32.dll", SetLastError = false)]
        private static extern bool GetLastInputInfo(ref Lastinputinfo plii);
        private static readonly DateTime SystemStartup = DateTime.Now.AddMilliseconds(-Environment.TickCount);

        [StructLayout(LayoutKind.Sequential)]
        private struct Lastinputinfo
        {
            public uint cbSize;
            public readonly int dwTime;
        }

        public static DateTime LastInput => SystemStartup.AddMilliseconds(LastInputTicks);

        public static TimeSpan IdleTime => DateTime.Now.Subtract(LastInput);

        private static int LastInputTicks
        {
            get
            {
                var lii = new Lastinputinfo {cbSize = (uint) Marshal.SizeOf(typeof(Lastinputinfo))};
                GetLastInputInfo(ref lii);
                return lii.dwTime;
            }
        }
    }
}

• .Net Development