Subclassing Windows in C#

image I’ve been toying around with creating an Outlook addin recently that adds a new panel to the main Outlook inspector window. Actually it is going to be a ‘folding’ or ‘collapsing’ windows similar to the docked ToolWindows in Visual Studio.image

Anyway, the stuff around getting the correct window handle for the Outlook inspector window and resizing it to allow some space to insert my new panel was fairly simple, but I also had to hook into the message look of the window so that I could capture any move or resize messages and so resize things again to accommodate my panel.

I had started developing it as an Outlook add-in but to speed things up (and prevent me having to register / unregister the addin between tests etc I decided to develop it as a separate app- I could still hook into Outlook and move things around.

The problem came when I was trying to hook the inspector window message loop – it didn’t seem to work. I fired up Spy++ and check that the inspector window was getting the messages – which it was – but they were never getting delivered to my hook code.

I was using System.Windows.Form.NativeWindow and overriding the WndProc function (see my NativeWindowListener class below). To get the hook in place I was creating a new NativeWindowListener class with the inspector window handle as the parameter. Checking the handles and the delegates etc it all seemed to be correct, I just couldn’t fathom why it wasn’t getting any of the messages.

Then the penny dropped. Outlook is in a separate process… (NativeWindow only works across the current process and window handles that are contained in it). What would be needed in this case is a system wide hook, that requires use of the Win32API and interop. I reckon this is overkill just to save a bit of development pain, so will probably move to something where the Outlook addin dynamically loads the panel in and make something available to have the add-in reload the panel – this should allow me to develop the panel code (the majority of the app) without worrying to much about the Outlook addin side of things.

using System;
using System.Windows.Forms;
using System.Text;

namespace Outlook_Subclasser
{
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
internal class NativeWindowListener : NativeWindow
{

    // Constant value was found in the "windows.h" header file.
    private const int WM_SIZE = 0x0005;

    public NativeWindowListener(IntPtr handle)
    {
        AssignHandle(handle);
    }

    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    protected override void WndProc(ref Message msg)
    {
        switch (msg.Msg)
        {
            case WM_SIZE:
                // do your processing in here
                break;

            default:
                break;
        }
        base.WndProc(ref msg);
    }
}
}

and then to use the class you would find the handle of the window you want to subclass and create a new NativeWindowsListener passing in that handle to the constructor. Note – this does not cover a number of aspects around releasing handles etc – you will want to make sure these are covered off…

MyForm myForm = new MyForm();
NativeWindowListener nwl = new NativeWindowListener(myForm.Handle);

 

GEO 51.4043197631836:-1.28760504722595

  • did you succeed in subclassing from a different process? could you please help if you have done so?