Use IMessageFilter
public partial class MyForm: Form, IMessageFilter
...
public ImageForm(Image initialImage)
{
InitializeComponent();
Application.AddMessageFilter(this);
}
/// <summary>
/// Filters out a message before it is dispatched.
/// </summary>
/// <returns>
/// true to filter the message and stop it from being dispatched; false to allow the message to continue to the next filter or control.
/// </returns>
/// <param name="m">The message to be dispatched. You cannot modify this message. </param><filterpriority>1</filterpriority>
public bool PreFilterMessage( ref Message m )
{
if (m.Msg.IsWindowMessage(WindowsMessages.MOUSEWHEEL)) //if (m.Msg == 0x20a)
{ // WM_MOUSEWHEEL, find the control at screen position m.LParam
var pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);
var hWnd = WindowFromPoint(pos);
if (hWnd != IntPtr.Zero && hWnd != m.HWnd && FromHandle(hWnd) != null)
{
SendMessage(hWnd, m.Msg, m.WParam, m.LParam);
return true;
}
}
return false;
}
[DllImport("user32.dll")]
private static extern IntPtr WindowFromPoint(Point pt);
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
also in form closing add:
Application.RemoveMessageFilter(this);
This will pick up an all windows messages (although only mousewheel is trapped here) - by using the mouseposition to find the control its over, you can then force windows to send the message to that control even if it has no focus.
NOTE: I have used WindowsMessages.MOUSEWHEEL which is from a class I have that enumerates the messages, just replace
if (m.Msg.IsWindowMessage(WindowsMessages.MOUSEWHEEL))
with the commented bit at the end
if (m.Msg == 0x20a)