Question

When left single click on the clock in the taskbar on Windows 7 (maybe Vista too) a popup opens showing calender and clock(s) (thus not the date and time adjust window). How do I open this window myself (preferred in C#)?

I was hoping timedate.cpl would call this, but this opens the date and time adjust window.

Answer 1

To show the clock you need to send the appropriate window message to the tray window. This can be done using the Windows API function SendMessage:

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Text;

class ShowCalendar
{
    private delegate bool EnumChildCallback(IntPtr hwnd, 
            ref IntPtr lParam);

    [DllImport("User32.dll")]
    private static extern bool EnumChildWindows(IntPtr hWndParent, 
            EnumChildCallback lpEnumFunc, 
            ref IntPtr lParam);

    [DllImport("User32.dll")]
    private static extern int GetClassName(IntPtr hWnd, 
        StringBuilder lpClassName, 
        int nMaxCount);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern IntPtr SendMessage(IntPtr hWnd, 
        UInt32 Msg, 
        IntPtr wParam, 
        IntPtr lParam);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern IntPtr FindWindow(string lpClassName, 
        string lpWindowName);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern IntPtr FindWindowEx(IntPtr hwndParent, 
        IntPtr hwndChildAfter, 
        string lpszClass, 
        string lpszWindow);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetWindowRect(IntPtr hWnd, 
            out RECT lpRect);

    [StructLayout(LayoutKind.Sequential)]
    private struct RECT
    {
        public int Left;        
        public int Top;         
        public int Right;       
        public int Bottom;      
    }

    private static readonly string TrayWndClassName = "Shell_TrayWnd";
    private static readonly string TrayNotifyWndClassName = "TrayNotifyWnd";
    private static readonly string ClockWndClassName = "TrayClockWClass";
    private static readonly uint WM_NCLBUTTONDOWN = 0x00A1;
    private static readonly uint HTCAPTION = 2;

    private static bool EnumChildProc(IntPtr hwndChild, ref IntPtr lParam)
    {
        StringBuilder className = new StringBuilder(128);
        GetClassName(hwndChild, className, 128);

        if (className.ToString() == ClockWndClassName)
        {
            lParam = hwndChild;
            return false;
        }
        return true;
    }


    static void Main(string[] args)
    {
        IntPtr hWndTray = FindWindow(TrayWndClassName, string.Empty);
        if (hWndTray == IntPtr.Zero)
        {
            throw new Win32Exception();
        }

        IntPtr hWndTrayNotify = FindWindowEx(hWndTray, 
            IntPtr.Zero, 
            TrayNotifyWndClassName, 
            string.Empty);
        if (hWndTrayNotify == IntPtr.Zero)
        {
            throw new Win32Exception();
        }

        // search clock window
        EnumChildCallback cb = new EnumChildCallback(EnumChildProc);
        IntPtr hWndClock = IntPtr.Zero;
        EnumChildWindows(hWndTray, cb, ref hWndClock);
        if (hWndClock == IntPtr.Zero)
        {
            throw new Win32Exception();
        }

        // get clock window position
        RECT rect;
        if (!GetWindowRect(hWndClock, out rect))
        {
            throw new Win32Exception();
        }

        // send click, lParam contains window position
        IntPtr wParam = new IntPtr(HTCAPTION);
        IntPtr lParam = new IntPtr(rect.Top << 16 | rect.Left);
        SendMessage(hWndTray, WM_NCLBUTTONDOWN, wParam, lParam);
    }
}