https://blogs.msdn.microsoft.com/calvin_hsia/2016/11/30/its-easy-to-use-windows-hooks-even-from-c/

C# Hooks.cs

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interop;

// Start Visual Studio
// File->New->Project->C#->WPF Application
// Replace MainWindow.Xaml.cs with this code

namespace WpfApp1
{
  /// <summary>
  /// Interaction logic for MainWindow.xaml
  /// </summary>
  public partial class MainWindow : Window
  {
    IntPtr _hook;
    IntPtr _hwnd;
    NativeMethods.CBTProc _callback;
    TextBox _txtStatus;
    CheckBox _chkBox;
    public MainWindow()
    {
      InitializeComponent();
      this.WindowState = WindowState.Maximized;
      // create an instance of the delegate that
      // won't be garbage collected to avoid:
      //   Managed Debugging Assistant 'CallbackOnCollectedDelegate' :** 
      //   'A callback was made on a garbage collected delegate of type 
      //   'WpfApp1!WpfApp1.MainWindow+NativeMethods+CBTProc::Invoke'. 
      //   This may cause application crashes, corruption and data loss. 
      //   When passing delegates to unmanaged code, they must be 
      //   kept alive by the managed application until it is guaranteed 
      //   that they will never be called.'
      _callback = this.CallBack;
      _hook = NativeMethods.SetWindowsHookEx(
          NativeMethods.HookType.WH_MOUSE,
          _callback,
          instancePtr: IntPtr.Zero,
          threadID: NativeMethods.GetCurrentThreadId());
      this.Closed += MainWindow_Closed;
      this.Loaded += MainWindow_Loaded;
    }

    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
      try
      {
        _txtStatus = new TextBox()
        {
          Margin = new Thickness(10, 0, 0, 0),
          MaxLines = 60,
          IsReadOnly = true,
          VerticalScrollBarVisibility = ScrollBarVisibility.Auto
        };
        _chkBox = new CheckBox()
        {
          Content = "Divert mouse messages",
          ToolTip = "try to move the mouse around and click on the window controls\r" +
            "You can reenable the mouse by using the keyboard\r" + 
            "(spacebar when the chkbox has focus) to uncheck this option\r"+
            "Notice that tooltips don't show when checkbox is checked"
        };
        var btn = new Button()
        {
          Content = "Click Me",
          ToolTip = "Now you see me",
          Width = 150,
          HorizontalAlignment = HorizontalAlignment.Left
        };
        btn.Click += (ob, eb) =>
        {
          AddStatusMsg("Thanks, I needed that");
        };
        var sp = new StackPanel()
        {
          Orientation = Orientation.Vertical
        };
        sp.Children.Add(
          new Label()
          {
            Content = "Move the mouse around"
          });
        sp.Children.Add(_chkBox);
        sp.Children.Add(btn);
        sp.Children.Add(_txtStatus);
        this.Content = sp;
        AddStatusMsg("Starting");
      }
      catch (Exception ex)
      {
        this.Content = ex.ToString();
      }
    }
    public void AddStatusMsg(string msg)
    {
      Dispatcher.BeginInvoke(new Action(
          () =>
          {
            var txt = DateTime.Now.ToString("MM/dd/yy HH:mm:ss:fff ") + msg;
            _txtStatus.AppendText(txt + "\r\n");
            _txtStatus.ScrollToEnd();
          }
          ));
    }

    private void MainWindow_Closed(object sender, EventArgs e)
    {
      if (_hook != IntPtr.Zero)
      {
        NativeMethods.UnhookWindowsHookEx(this._hook);
      }
    }

    private IntPtr CallBack(int code, IntPtr wParam, IntPtr lParam)
    {
      var wind = Window.GetWindow(this);
      if (_hwnd == null)
      {
        _hwnd = (new WindowInteropHelper(wind)).EnsureHandle();
      }
      var mouseInfo = Marshal.PtrToStructure<NativeMethods.MOUSEHOOKSTRUCT>(lParam);
      AddStatusMsg($"{code} wParam {wParam} lParam {lParam} {mouseInfo}");
      if (_chkBox.IsChecked == true)
      {
        return new IntPtr(1); // non-zero indicates don't pass to target
      }
      return NativeMethods.CallNextHookEx(IntPtr.Zero, code, wParam, lParam);
    }

    private static class NativeMethods
    {
      [StructLayout(LayoutKind.Sequential)]
      public struct MOUSEHOOKSTRUCT
      {
        public POINT pt; // Can't use System.Windows.Point because that has X,Y as doubles, not integer
        public IntPtr hwnd;
        public uint wHitTestCode;
        public IntPtr dwExtraInfo;
        public override string ToString()
        {
          return $"({pt.X,4},{pt.Y,4})";
        }
      }

#pragma warning disable 649 // CS0649: Field 'MainWindow.NativeMethods.POINT.Y' is never assigned to, and will always have its default value 0
      public struct POINT
      {
        public int X;
        public int Y;
      }
#pragma warning restore 649

      // from WinUser.h
      public enum HookType
      {
        WH_MIN = (-1),
        WH_MSGFILTER = (-1),
        WH_JOURNALRECORD = 0,
        WH_JOURNALPLAYBACK = 1,
        WH_KEYBOARD = 2,
        WH_GETMESSAGE = 3,
        WH_CALLWNDPROC = 4,
        WH_CBT = 5,
        WH_SYSMSGFILTER = 6,
        WH_MOUSE = 7,
        WH_HARDWARE = 8,
        WH_DEBUG = 9,
        WH_SHELL = 10,
        WH_FOREGROUNDIDLE = 11,
        WH_CALLWNDPROCRET = 12,
        WH_KEYBOARD_LL = 13,
        WH_MOUSE_LL = 14
      }
      public enum HookCodes
      {
        HC_ACTION = 0,
        HC_GETNEXT = 1,
        HC_SKIP = 2,
        HC_NOREMOVE = 3,
        HC_NOREM = HC_NOREMOVE,
        HC_SYSMODALON = 4,
        HC_SYSMODALOFF = 5
      }
      public enum CBTHookCodes
      {
        HCBT_MOVESIZE = 0,
        HCBT_MINMAX = 1,
        HCBT_QS = 2,
        HCBT_CREATEWND = 3,
        HCBT_DESTROYWND = 4,
        HCBT_ACTIVATE = 5,
        HCBT_CLICKSKIPPED = 6,
        HCBT_KEYSKIPPED = 7,
        HCBT_SYSCOMMAND = 8,
        HCBT_SETFOCUS = 9
      }

      public delegate IntPtr CBTProc(int code, IntPtr wParam, IntPtr lParam);

      [DllImport("user32.dll")]
      [return: MarshalAs(UnmanagedType.Bool)]
      public static extern bool UnhookWindowsHookEx(IntPtr hookPtr);

      [DllImport("user32.dll")]
      public static extern IntPtr CallNextHookEx(IntPtr hookPtr, int nCode, IntPtr wordParam, IntPtr longParam);

      [DllImport("user32.dll")]
      public static extern IntPtr SetWindowsHookEx(HookType hookType, CBTProc hookProc, IntPtr instancePtr, uint threadID);

      [DllImport("kernel32.dll")]
      public static extern uint GetCurrentThreadId();
    }
  }

}