Cannot use pinvoke to send WM_CLOSE to a Windows Explorer window

Question

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);

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

Answer 1

It may be a security feature. There used to be many viruses that would WM_CLOSE Windows Explorer to prevent you from exploring and deleting the virus files. My guess is that you can't pinvoke close Task Manager anymore either, although that's just a guess.

Answer 2

One way to close explorer is to find the explorer.exe process via Process.GetProcesses(), then calling Kill() on the process. However, I suspect Windows has some built-in mechanism to restart explorer if it is killed.

A better question might be, why do you need to close explorer?

Answer 3

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