C# Process.MainWindowHandle always returns IntPtr Zero

Solution 1:

The main window is the window opened by the process that currently has the focus (the TopLevel form). You must use the Refresh method to refresh the Process object to get the current main window handle if it has changed.

You can get the MainWindowHandle property only for processes that are running on the local computer. The MainWindowHandle property is a value that uniquely identifies the window that is associated with the process.

A process has a main window associated with it only if the process has a graphical interface. If the associated process does not have a main window, the MainWindowHandle value is zero. The value is also zero for processes that have been hidden, that is, processes that are not visible in the taskbar. This can be the case for processes that appear as icons in the notification area, at the far right of the taskbar.

If you have just started a process and want to use its main window handle, consider using the WaitForInputIdle method to allow the process to finish starting, ensuring that the main window handle has been created. Otherwise, an exception will be thrown.

Solution 2:

while (!proc.HasExited)
{
    proc.Refresh();
    if (proc.MainWindowHandle.ToInt32() != 0)
    {
        return proc.MainWindowHandle;
    }
}

Solution 3:

A workaround is to enumerate through all top-level windows and examine their process ids until you find a match...

    [DllImport("user32.dll")]
    public static extern IntPtr FindWindowEx(IntPtr parentWindow, IntPtr previousChildWindow, string windowClass, string windowTitle);

    [DllImport("user32.dll")]
    private static extern IntPtr GetWindowThreadProcessId(IntPtr window, out int process);

    private IntPtr[] GetProcessWindows(int process) {
        IntPtr[] apRet = (new IntPtr[256]);
        int iCount = 0;
        IntPtr pLast = IntPtr.Zero;
        do {
            pLast = FindWindowEx(IntPtr.Zero, pLast, null, null);
            int iProcess_;
            GetWindowThreadProcessId(pLast, out iProcess_);
            if(iProcess_ == process) apRet[iCount++] = pLast;
        } while(pLast != IntPtr.Zero);
        System.Array.Resize(ref apRet, iCount);
        return apRet;
    }