How to handle WndProc messages in WPF?

You can do this via the System.Windows.Interop namespace which contains a class named HwndSource.

Example of using this

using System;
using System.Windows;
using System.Windows.Interop;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        protected override void OnSourceInitialized(EventArgs e)
        {
            base.OnSourceInitialized(e);
            HwndSource source = PresentationSource.FromVisual(this) as HwndSource;
            source.AddHook(WndProc);
        }

        private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            // Handle messages...

            return IntPtr.Zero;
        }
    }
}

Completely taken from the excellent blog post: Using a custom WndProc in WPF apps by Steve Rands

Actually, as far as I understand such a thing is indeed possible in WPF using HwndSource and HwndSourceHook. See this thread on MSDN as an example. (Relevant code included below)

// 'this' is a Window
HwndSource source = HwndSource.FromHwnd(new WindowInteropHelper(this).Handle);
source.AddHook(new HwndSourceHook(WndProc));

private static IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    //  do stuff

    return IntPtr.Zero;
}

Now, I'm not quite sure why you'd want to handle Windows Messaging messages in a WPF application (unless it's the most obvious form of interop for working with another WinForms app). The design ideology and the nature of the API is very different in WPF from WinForms, so I would suggest you just familiarise yourself with WPF more to see exactly why there is no equivalent of WndProc.

HwndSource src = HwndSource.FromHwnd(new WindowInteropHelper(this).Handle);
src.AddHook(new HwndSourceHook(WndProc));


.......


public IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{

  if(msg == THEMESSAGEIMLOOKINGFOR)
    {
      //Do something here
    }

  return IntPtr.Zero;
}

There are ways to handle messages with a WndProc in WPF (e.g. using a HwndSource, etc.), but generally those techniques are reserved for interop with messages that can't directly be handled through WPF. Most WPF controls aren't even windows in the Win32 (and by extension Windows.Forms) sense, so they won't have WndProcs.

WPF doesn't operate on WinForms type wndprocs

You can host an HWndHost in an appropriate WPF element then override the Hwndhost's wndproc, but AFAIK that's as close as you're going to get.

http://msdn.microsoft.com/en-us/library/ms742522.aspx

http://blogs.msdn.com/nickkramer/archive/2006/03/18/554235.aspx

The short answer is you can't. WndProc works by passing messages to a HWND on a Win32 level. WPF windows have no HWND and hence can't participate in WndProc messages. The base WPF message loop does sit on top of WndProc but it abstracts them away from core WPF logic.

You can use a HWndHost and get at a WndProc for it. However this is almost certainly not what you want to do. For the majority of purposes, WPF does not operate on HWND and WndProc. Your solution almost certainly relies on making a change in WPF not in WndProc.