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VC++ MFC Codes: Display Message Balloon Tip Window with SetWindowRgn and CreateRectRgn and CombineRgn

 
 

Sample Image - MessageBalloons.jpg

Introduction

There are times when one would like to display messages in an non-obtrusive way. Message Balloons are one of the new ways. Message Balloons are taking precedence over message boxes for small display messages as they even prevent the user from clicking an �OK� and still get the message across. These kind of Message Balloons are becoming a part of standard user interface with MSN explorer and Windows XP. Still no library has been provided for making these balloons. Hence this attempt.

How to use the class provided ?

Include the following two files in your project:

  • BalloonTip.h
  • BalloonTip.cpp

There are two interfaces to create and show the message balloons.

  • CBalloonTip::Show()
  • CBalloonTip::Hide()

CBalloonTip::Show()-:

This is a pseudo constructor because we want to force heap creation of the balloon, so that it remains in the memory even after it has been called. It will be automatically destroyed when a it receives a WM_TIMER message which is set in the CBalloon::MakeVisible(). The other method to destroy the Balloon before the timer ticks is to call the static function CBalloon::Hide(). The constructor for CBalloonTip is protected, hence this helps in forcing heap creation. The following code shows how to create a Message Balloon and show it.

Collapse Copy Code
LOGFONT lf;
::ZeroMemory (&lf, sizeof (lf));
lf.lfHeight = 16;
lf.lfWeight = FW_BOLD;
lf.lfUnderline = FALSE;
::strcpy (lf.lfFaceName, _T("Arial"));
        
CBalloonTip::Show(
    CPoint(200, 200),         // Point on the screen where the tip will be shown
    CSize(250, 100),          // Size of the total rectangle encompassing the balloon 
    _T("Please enter a password !!"), // Message to be shown in the balloon
    lf,                               // LOGFONT structure for font properties 
    5,                 // Time in seconds to show the balloon
    FALSE              // TRUE  == Balloon is up(Balloon Tip is down) 
                       // FALSE ==  Balloon is down(Balloon Tip is up)
);

CBalloonTip::Hide()-:

This is for destroying the Balloon for any particular condition that may arise before it is automatically destroyed in the CBalloonTip::OnTimer(). Either way if CBalloonTip::Hide() is not called the Balloon is destroyed in CBalloonTip::OnTimer(). So the caller (user of this class) does not need to worry about the memory cleanup.

Class Design Details

CBalloonTip is derived from CFrameWnd. The balloon is created from the combination of two regions, one is a polygon region to show the the Balloon Tip and the other is a Round Rectangle region. This is done in the CBalloonTip::OnCreate().

Collapse Copy Code
int CBalloonTip::OnCreate(LPCREATESTRUCT lpCreateStruct) 
{
    //..........Some code
    //...................

    CRgn rgnComb;	
    
    rgnComb.CreateRectRgn(t_Rect.left, t_Rect.top, t_Rect.right, t_Rect.bottom);
		
    int iRetComb = rgnComb.CombineRgn(&m_rgnTip, &m_rgnRoundRect, RGN_OR);
}

The m_rgnTip and m_rgnRoundRect are created with different calculations depending upon whether the balloon tip is down or up. The visible window or balloon region is finally set using SetWindowRgn (rgnComb.operator HRGN(), TRUE) in the CBalloonTip::OnCreate().

The Balloon window is not shown up in the tucancode.netbar by making the Balloon a child of an invisible parent in CBalloonTip::PreCreateWindow() This parent window is a member variable (CBalloon::m_wndInvisibleParent) of the class itself and is destroyed automatically when the Balloon is destroyed. So the non-appearance of the Balloon window in the tucancode.net bar is taken care of automatically.

Collapse Copy Code
BOOL CBalloonTip::PreCreateWindow(CREATESTRUCT& cs)
{
    //...............Some code
    //........................

    if (!::IsWindow(m_wndInvisibleParent.m_hWnd))
    {
        // Try creating the invisible parent window
        PCSTR pstrOwnerClass = ::AfxRegisterWndClass(0);
       
        BOOL bError = m_wndInvisibleParent.CreateEx(
                          0,
                          pstrOwnerClass, 
                          _T(""), 
                          WS_POPUP,
	                  0,
                          0,
                          0,
                          0,
		          NULL,
                          0
                      );
    }
}

Window Creation

The balloon is created with respect from the point where it is supposed to be displayed. So the calculation of balloon rectangle has to be recalculated w.r.t. the point at which it is to be shown. Different calculations have to be done if the Balloon tip is down or up. This is done in CBalloontip::Show() as shown below.

Collapse Copy Code
CBalloonTip* CBalloonTip::Show(CPoint pt, CSize size, CString strMessage, 
        LOGFONT lf, UINT nSecs, BOOL bBalloonUp)
{
    //.........Some code
    //..................

    if (bBalloonUp)
    {
        nRectLeft   = pt.x - (size.cx * 0.65);
        nRectRight  = pt.x + (size.cx * 0.35);
        nRectTop    = pt.y - size.cy;
        nRectBottom = pt.y;
    }
    else
    {
        nRectLeft   = pt.x - (size.cx * 0.35);
        nRectRight  = pt.x + (size.cx * 0.65);
        nRectTop    = pt.y;
        nRectBottom = pt.y + (size.cy);
    }
}

The actual Windows� window balloon is created in CBalloonTip::Show() using

Collapse Copy Code
pBalloonTip->Create(CRect(nRectLeft, nRectTop, nRectRight, nRectBottom));

The CRect passed in the above function will represent the actual position of the balloon in screen co-ordinates. The timer for the Balloon destruction is set in the next line in CBalloonTip::Show()

Collapse Copy Code
pBalloonTip->MakeVisisble(nSecs);
  • Only one instance of the Balloon is allowed to created at a time using the static variable CBalloonTip::nBalloonInstances

Overview of the demo project

Demo

Just try clicking the "OK" button without entering anything in the the edit boxes.

Compatibility

Tested using VC++ 6 with MFC on Windows 2000. Should work fine on other Windows OSs(95/98/NT/ME/XP) also, as it uses no OS specific code.

Updates

The following changes to the code in the updated version have been made:

  1. The OnPaint and Show methods have been updated to do a better job.
  2. The message balloon doesn't stay on top of applications as you switch between apps.
  3. There is more rigorous checking to prevent crashes as a result of null pointers, etc...

Conclusion

I hope that this contribution will make some improvement in the user interface code of your forthcoming programs!!! Any suggestions, improvements or bugs detected are welcome. Enjoy...

 

 

 

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