Finding the position and dimensions of the Windows system tray

Introduction

In my Tray Calendar application I wanted to make the "About" box and Options dialog appear to expand and contract into and out of the system tray. The animation was taken care of by using the DrawAnimatedRects function (see the article "Using the DrawAnimatedRects() function"), but I need to know where the system tray was.

Finding the System Tray

My first thought was to simply use FindWindow using the window name "TrayNotifyWnd", but unfortunately this did not work as planned. Instead I was able to get a handle to "Shell_TrayWnd", and from there work my way down using EnumChildWindows to get a hold of the system tray and the clock window. Subtracting the size of the system clock window from that of the system tray then gave me the working area of the system tray.

The code is shown below:

BOOL CALLBACK FindTrayWnd(HWND hwnd, LPARAM lParam)
{
    // lParam will contain a pointer to a CRect structure that will be used to 
    // store the coordinates of the tray

    TCHAR szClassName[256];
    GetClassName(hwnd, szClassName, 255);

    // Did we find the Main System Tray? If so, then get its size and keep going
    if (_tcscmp(szClassName, _T("TrayNotifyWnd")) == 0)
    {
        CRect *pRect = (CRect*) lParam;
        ::GetWindowRect(hwnd, pRect);
        return TRUE;
    }

    // Did we find the System Clock? If so, then adjust the size of 
    // the rectangle we have and quit (clock will be found after the 
    // system tray)
    if (_tcscmp(szClassName, _T("TrayClockWClass")) == 0)
    {
        CRect *pRect = (CRect*) lParam;
        CRect rectClock;
        ::GetWindowRect(hwnd, rectClock);
        
        // The system clock may be either to the right or above the system 
        // tray area. Adjust accordingly
        if (rectClock.bottom < lpRect->bottom-5)  // 5 = fudge factor
            lpRect->top = rectClock.bottom;
        else
            lpRect->right = rectClock.left;
        return FALSE;
    }
 
    return TRUE;
}
 
void GetTrayWndRect(LPRECT lprect)
{
#define DEFAULT_RECT_WIDTH 150
#define DEFAULT_RECT_HEIGHT 30

    HWND hShellTrayWnd = ::FindWindow(_T("Shell_TrayWnd"), NULL);
    if (hShellTrayWnd)
    {
        ::GetWindowRect(hShellTrayWnd, lprect);
        EnumChildWindows(hShellTrayWnd, FindTrayWnd, (LPARAM)lprect);
        return;
    }
    // OK, we failed to get the rect from the quick hack. Either explorer isn't
    // running or it's a new version of the shell with the window class names
    // changed (how dare Microsoft change these undocumented class names!) So, we
    // try to find out what side of the screen the taskbar is connected to. We
    // know that the system tray is either on the right or the bottom of the
    // taskbar, so we can make a good guess at where to minimize to
    APPBARDATA appBarData;
    appBarData.cbSize=sizeof(appBarData);
    if (SHAppBarMessage(ABM_GETTASKBARPOS,&appBarData))
    {
        // We know the edge the taskbar is connected to, so guess the rect of the
        // system tray. Use various fudge factor to make it look good
        switch(appBarData.uEdge)
        {
        case ABE_LEFT:
        case ABE_RIGHT:
            // We want to minimize to the bottom of the taskbar
            lprect->top    = appBarData.rc.bottom-100;
            lprect->bottom = appBarData.rc.bottom-16;
            lprect->left   = appBarData.rc.left;
            lprect->right  = appBarData.rc.right;
            break;
            
        case ABE_TOP:
        case ABE_BOTTOM:
            // We want to minimize to the right of the taskbar
            lprect->top    = appBarData.rc.top;
            lprect->bottom = appBarData.rc.bottom;
            lprect->left   = appBarData.rc.right-100;
            lprect->right  = appBarData.rc.right-16;
            break;
        }
        return;
    }
    
    // Blimey, we really aren't in luck. It's possible that a third party shell
    // is running instead of explorer. This shell might provide support for the
    // system tray, by providing a Shell_TrayWnd window (which receives the
    // messages for the icons) So, look for a Shell_TrayWnd window and work out
    // the rect from that. Remember that explorer's taskbar is the Shell_TrayWnd,
    // and stretches either the width or the height of the screen. We can't rely
    // on the 3rd party shell's Shell_TrayWnd doing the same, in fact, we can't
    // rely on it being any size. The best we can do is just blindly use the
    // window rect, perhaps limiting the width and height to, say 150 square.
    // Note that if the 3rd party shell supports the same configuraion as
    // explorer (the icons hosted in NotifyTrayWnd, which is a child window of
    // Shell_TrayWnd), we would already have caught it above
    if (hShellTrayWnd)
    {
        ::GetWindowRect(hShellTrayWnd, lprect);
        if (lprect->right - lprect->left > DEFAULT_RECT_WIDTH)
            lprect->left = lprect->right - DEFAULT_RECT_WIDTH;
        if (lprect->bottom - lprect->top > DEFAULT_RECT_HEIGHT)
            lprect->top = lprect->bottom - DEFAULT_RECT_HEIGHT;
        
        return;
    }
    
    // OK. Haven't found a thing. Provide a default rect based on the current work
    // area
    SystemParametersInfo(SPI_GETWORKAREA,0,lprect, 0);
    lprect->left = lprect->right - DEFAULT_RECT_WIDTH;
    lprect->top  = lprect->bottom - DEFAULT_RECT_HEIGHT;
}

Updates

Compensation was made for the case where the system clock is above the system tray, and Matthew Ellis improved the GetTrayWndRect to provide more fallbacks.