vsdingextension/VsDingExtensionProject/WinApiHelper.cs

namespace VitaliiGanzha.VsDingExtension
{
    using System;
    using System.Diagnostics;
    using System.Runtime.InteropServices;

    public static class NativeMethods
    {
        [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
        private static extern IntPtr GetForegroundWindow();

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern int GetWindowThreadProcessId(IntPtr handle, out int processId);

        public static bool ApplicationIsActivated()
        {
            var activatedHandle = GetForegroundWindow();
            if (activatedHandle == IntPtr.Zero)
            {
                return false;       // No window is currently activated
            }
            var procId = Process.GetCurrentProcess().Id;
            int activeProcId;
            GetWindowThreadProcessId(activatedHandle, out activeProcId);
            return activeProcId == procId;
        }
    }
}