How can I register a global hot key to say CTRL+SHIFT+(LETTER) using WPF and .NET 3.5?

I'm not sure of what you mean by "global" here, but here it goes (I'm assuming you mean a command at the application level, for example, Save All that can be triggered from anywhere by Ctrl + Shift + S.)

You find the global UIElement of your choice, for example, the top level window which is the parent of all the controls where you need this binding. Due to "bubbling" of WPF events, events at child elements will bubble all the way up to the root of the control tree.

Now, first you need

1. to bind the Key-Combo with a Command using an InputBinding like this
2. you can then hookup the command to your handler (e.g. code that gets called by SaveAll) via a CommandBinding.

For the Windows Key, you use the right Key enumerated member, Key.LWin or Key.RWin

public WindowMain()
{
   InitializeComponent();

   // Bind Key
   var ib = new InputBinding(
       MyAppCommands.SaveAll,
       new KeyGesture(Key.S, ModifierKeys.Shift | ModifierKeys.Control));
   this.InputBindings.Add(ib);

   // Bind handler
   var cb = new CommandBinding( MyAppCommands.SaveAll);
   cb.Executed += new ExecutedRoutedEventHandler( HandlerThatSavesEverthing );

   this.CommandBindings.Add (cb );
}

private void HandlerThatSavesEverthing (object obSender, ExecutedRoutedEventArgs e)
{
  // Do the Save All thing here.
}

If you're going to mix Win32 and WPF, here's how I did it:

using System;
using System.Runtime.InteropServices;
using System.Windows.Interop;
using System.Windows.Media;
using System.Threading;
using System.Windows;
using System.Windows.Input;

namespace GlobalKeyboardHook
{
    public class KeyboardHandler : IDisposable
    {

        public const int WM_HOTKEY = 0x0312;
        public const int VIRTUALKEYCODE_FOR_CAPS_LOCK = 0x14;

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vlc);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool UnregisterHotKey(IntPtr hWnd, int id);

        private readonly Window _mainWindow;
        WindowInteropHelper _host;

        public KeyboardHandler(Window mainWindow)
        {
            _mainWindow = mainWindow;
            _host = new WindowInteropHelper(_mainWindow);

            SetupHotKey(_host.Handle);
            ComponentDispatcher.ThreadPreprocessMessage += ComponentDispatcher_ThreadPreprocessMessage;
        }

        void ComponentDispatcher_ThreadPreprocessMessage(ref MSG msg, ref bool handled)
        {
            if (msg.message == WM_HOTKEY)
            {
                //Handle hot key kere
            }
        }

        private void SetupHotKey(IntPtr handle)
        {
            RegisterHotKey(handle, GetType().GetHashCode(), 0, VIRTUALKEYCODE_FOR_CAPS_LOCK);
        }

        public void Dispose()
        {
            UnregisterHotKey(_host.Handle, GetType().GetHashCode());
        }
    }
}

You can get the virtual-key code for the hotkey you want to register here: http://msdn.microsoft.com/en-us/library/ms927178.aspx

There may be a better way, but this is what I've got so far.

Cheers!

With the NHotKey package, you can make your hotkey global:

• https://github.com/thomaslevesque/NHotkey
• https://thomaslevesque.com/2014/02/05/wpf-declare-global-hotkeys-in-xaml-with-nhotkey/ (use web.archive.org if the link is broken)

In short, for XAML, all you need to do is to replace

<KeyBinding Gesture="Ctrl+Alt+Add" Command="{Binding IncrementCommand}" />

by

<KeyBinding Gesture="Ctrl+Alt+Add" Command="{Binding IncrementCommand}"
            HotkeyManager.RegisterGlobalHotkey="True" />

I'm not sure about WPF, but this may help. I used the solution described in RegisterHotKey (user32) (modified to my needs of course) for a C# Windows Forms application to assign a CTRL-KEY combination within Windows to bring up a C# form, and it worked beautifully (even on Windows Vista). I hope it helps and good luck!

RegisterHotKey() suggested by John could work - the only catch is that it requires an HWND (using PresentationSource.FromVisual(), and casting the result to an HwndSource).

However, you'll also need to respond to the WM_HOTKEY message - I'm not sure if there is a way to get access to the WndProc of a WPF window or not (which can be done for Windows Forms windows).