Cannot use pinvoke to send WM_CLOSE to a Windows Explorer window

I have a C# application that uses the SendMessage pinvoke method to send a "close window" message (WM_CLOSE / 16) to various windows outside the application. This works great, except when the window in question is a Windows Explorer window. I do not get an exception, but the window does not close.

Here's the signature:

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
    internal static extern IntPtr SendMessage(HandleRef hWnd, uint Msg, IntPtr wParam, IntPtr lParam开发者_JS百科);

Is there a different message that I need to send to Windows Explorer windows? Or an alternate way to accomplish this?

an alternative solution would be to use PostMessage win API call instead of SendMessage, below is an example which worked fine for me (I'm using winXP sp3):

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
[DllImport("user32.Dll")]
public static extern int PostMessage(IntPtr hWnd, UInt32 msg, int wParam, int lParam);

private const UInt32 WM_CLOSE          = 0x0010;

...

    IntPtr hWnd = FindWindow("ExploreWClass", null);
    if (hWnd.ToInt32()!=0) PostMessage(hWnd, WM_CLOSE, 0, 0);

differences between PostMessage and SendMessage api call are described here: http://msdn.microsoft.com/en-us/magazine/cc301431.aspx