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How to make a resizable dialog bar in Microsoft Foundation Classes (MFC)

This article was previously published under Q143255
Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code.
SUMMARY
The default MFC implementation of CDialogBar does not allow for the dialog bar to be resizable when it is floating. If the dialog bar contains controls that are sensibly resized, the programmer may want to make the dialog bar resizable by using the technique described in this article.

To make the dialog bar resizable when using versions of MFC earlier than version 4.0:
  1. Change the style of the mini frame window enclosing the floating dialog bar so that it is resizable.
  2. Override CDialogBar to provide a CalcFixedLayout, which allows the dialog bar and its controls to be resized.
To make the dialog bar resizable when using MFC version 4.0 or later, you can use the built-in support for resizable control bars. However, dialog bars do not get this behavior by default. To make a dialog bar resizable:
  1. Use the new CBRS_SIZE_DYNAMIC style when creating the dialog bar.
  2. Add code to an override of the new CalcDynamicLayout() function.
MORE INFORMATION
For more information about how to create a DialogBar class, click the following article number to view the article in the Microsoft Knowledge Base:
185672 How to initialize child controls in a derived CDialogBar

For versions of MFC earlier than version 4.0

CDialogBar contains an embedded member variable m_sizeDefault of type CSize. On creation, m_sizeDefault is set to the size of the dialog template embedded in the dialog bar. Whenever the dialog bar is resized or repositioned, MFC calls CDialogBar::CalcFixedLayout(). This member function is intended to return the appropriate size of the control bar; for CDialogBar, CalcFixedLayout() usually returns m_sizeDefault. This causes the dialog bar to always snap back to its default size.

To create a resizable dialog bar, you must ensure that the following things are handled in some manner by an application:
  1. The CMiniDockFrameWnd surrounding the floating dialog bar must have its window styles changed so that it is resizable.
  2. A member variable must be added to a class derived from CDialogBar to represent the appropriate floating size.
  3. CalcFixedLayout() must be overridden in this class to set and return the floating size of the dialog bar when the dialog bar is being resized.
With the appropriate tests, both 1 and 3 can be implemented in CalcFixedLayout(). See the "Sample Code" section of this article for an example of this.

For MFC version 4.0 and later

In MFC 4.0 and higher, control bars support the new CBRS_SIZE_DYNAMIC style. CBRS_SIZE_DYNAMIC allows a floating control bar to be dynamically resized when the user drags the control bar's border. The virtual function CControlBar::CalcDynamicLayout() has been added to determine the size that a control bar should be resized to.

CalcDynamicLayout() is called for CBRS_SIZE_DYNAMIC control bars when the border of a floating control bar is dragged and when the control bar is docked or floated. The default CControlBar implementation simply calls CalcFixedLayout(), which prevents control bar objects from resizing unless CalcDynamicLayout() is overridden. CDialogBar does not override CalcDynamicLayout(), so by default, dialog bars are not resizable.

Therefore, to make a resizable dialog bar using MFC 4.0:
  1. Create a new class derived from CDialogBar and override the CalcDynamicLayout() function. Depending on the behavior you want, it may be necessary to add a member variable to the class.
  2. Create an instance of this class using the CBRS_SIZE_DYNAMIC style bit. Dialog bars are typically created in CMainFrame::OnCreate():
          if (!m_wndDialogBar.Create(this, IDD_DIALOGBAR,                                 CBRS_TOP | CBRS_SIZE_DYNAMIC, 777))      {         TRACE0("Failed to create dialogbar\n");         return -1;      }      m_wndDialogBar.EnableDocking(CBRS_ALIGN_ANY);      DockControlBar(&m_wndDialogBar); 						

Note You must use the WS_CHILD style with the IDD_DIALOGBAR dialog template. Do not use the WS_VISIBLE style or any other style.

See the "Sample Code" section in this article for a examples of this.

Sample code

Sample code for MFC versions prior to Visual C++ 4.0

   /* Compile options needed: Default   */    // RSZDLGBR.H : header file   //    class CResizableDlgBar : public CDialogBar   {   // Construction   public:        BOOL Create( CWnd* pParentWnd, UINT nIDTemplate, UINT nStyle,                    UINT nID, BOOL = TRUE);        BOOL Create( CWnd* pParentWnd, LPCTSTR lpszTemplateName,                 UINT nStyle, UINT nID, BOOL = TRUE);   // Attributes   public:        CSize m_sizeDocked;        CSize m_sizeFloating;        BOOL m_bChangeDockedSize;   // Indicates whether to keep                                 // a default size for docking   // Operations   public:   // Overrides       virtual CSize CalcFixedLayout(BOOL bStretch, BOOL bHorz);   // Implementation   public:   };   /////////////////////////////////////////////////////////////////////    // RSZDLGBR.CPP : implementation file   //    #include "stdafx.h"   #include <afxpriv.h>   #include "ResizableDlgBar.h"   #include "resource.h"   ////////////////////////////////////////////////////////////////////    // CResizableDlgBar Construction/Destruction   BOOL CResizableDlgBar::Create( CWnd* pParentWnd, UINT nIDTemplate,                                  UINT nStyle, UINT nID, BOOL bChange)   {        if(!CDialogBar::Create(pParentWnd,nIDTemplate,nStyle,nID))             return FALSE;        m_bChangeDockedSize = bChange;        m_sizeFloating = m_sizeDocked = m_sizeDefault;        return TRUE;   }   BOOL CResizableDlgBar::Create( CWnd* pParentWnd,                                  LPCTSTR lpszTemplateName,                                  UINT nStyle, UINT nID, BOOL bChange)   {        if (!CDialogBar::Create( pParentWnd, lpszTemplateName,                                nStyle, nID))             return FALSE;        m_bChangeDockedSize = bChange;        m_sizeFloating = m_sizeDocked = m_sizeDefault;        return TRUE;   }   ////////////////////////////////////////////////////////////////////    // Overloaded functions   CSize CResizableDlgBar::CalcFixedLayout(BOOL bStretch, BOOL bHorz)   {        if (IsFloating())       {           // Get the parent mini frame wnd           CMiniDockFrameWnd* pFrame =             ((CMiniDockFrameWnd*)m_pDockBar->GetParent());           CRect rcFrame;           pFrame->GetClientRect(&rcFrame);           // Is its size (0,0)? If so, it was just floated           CSize sizerc(rcFrame.right - rcFrame.left,                        rcFrame.bottom - rcFrame.top);           if (!((sizerc.cx <= 0) && (sizerc.cy <= 0)))               return ((m_bChangeDockedSize) ?                           m_sizeDocked = m_sizeFloating = sizerc :                           m_sizeFloating = sizerc);           else           {               // Modify Style when dialog bar is first floated               pFrame->ModifyStyle(MFS_MOVEFRAME, WS_THICKFRAME, 0);               m_dwStyle |= MFS_THICKFRAME;               m_dwStyle |= WS_THICKFRAME;               m_dwStyle &= ~MFS_MOVEFRAME;               // Return last floated size               return m_sizeFloating;           }       }        if (bStretch) // if not docked stretch to fit             return CSize(bHorz ? 32767 : m_sizeDocked.cx,                  bHorz ? m_sizeDocked.cy : 32767);        else             return m_sizeDocked;   }				

Sample code for MFC included with Visual C++ 4.0 and above

   /* Compile options needed: Default   */    // ResizableDlgBar.h : header file   //    class CResizableDlgBar : public CDialogBar   {   // Construction   public:        BOOL Create( CWnd* pParentWnd, UINT nIDTemplate, UINT nStyle,                     UINT nID, BOOL = TRUE);        BOOL Create( CWnd* pParentWnd, LPCTSTR lpszTemplateName,                     UINT nStyle, UINT nID, BOOL = TRUE);   // Attributes   public:        CSize m_sizeDocked;        CSize m_sizeFloating;        BOOL m_bChangeDockedSize;   // Indicates whether to keep                                    // a default size for docking   // Operations   public:   // Overrides       // ClassWizard generated virtual function overrides       //<AngularNoBind>{{</AngularNoBind>AFX_VIRTUAL(CResizableDlgBar)       //}}AFX_VIRTUAL       virtual CSize CalcDynamicLayout( int nLength, DWORD dwMode );   // Implementation   public:   // Generated message map functions   protected:       //<AngularNoBind>{{</AngularNoBind>AFX_MSG(CResizableDlgBar)       // NOTE - the ClassWizard will add and remove member functions here.       //}}AFX_MSG       DECLARE_MESSAGE_MAP()   };   /////////////////////////////////////////////////////////////////////    // ResizableDlgBar.cpp : implementation file   //    #include "stdafx.h"   #include "ResizableDlgBar.h"   ////////////////////////////////////////////////////////////////////    // CResizableDlgBar Construction/Destruction   BOOL CResizableDlgBar::Create( CWnd* pParentWnd, UINT nIDTemplate,                                  UINT nStyle, UINT nID, BOOL bChange)   {        if(!CDialogBar::Create(pParentWnd,nIDTemplate,nStyle,nID))             return FALSE;        m_bChangeDockedSize = bChange;        m_sizeFloating = m_sizeDocked = m_sizeDefault;        return TRUE;   }   BOOL CResizableDlgBar::Create( CWnd* pParentWnd,                                  LPCTSTR lpszTemplateName, UINT nStyle,                                  UINT nID, BOOL bChange)   {       if (!CDialogBar::Create( pParentWnd, lpszTemplateName,                                                 nStyle, nID))           return FALSE;       m_bChangeDockedSize = bChange;       m_sizeFloating = m_sizeDocked = m_sizeDefault;       return TRUE;   }   ////////////////////////////////////////////////////////////////////    // Overloaded functions   CSize CResizableDlgBar::CalcDynamicLayout(int nLength, DWORD dwMode)   {       // Return default if it is being docked or floated       if ((dwMode & LM_VERTDOCK) || (dwMode & LM_HORZDOCK))       {           if (dwMode & LM_STRETCH) // if not docked stretch to fit               return CSize((dwMode & LM_HORZ) ? 32767 : m_sizeDocked.cx,                            (dwMode & LM_HORZ) ? m_sizeDocked.cy : 32767);             else               return m_sizeDocked;       }       if (dwMode & LM_MRUWIDTH)           return m_sizeFloating;       // In all other cases, accept the dynamic length       if (dwMode & LM_LENGTHY)           return CSize(m_sizeFloating.cx, (m_bChangeDockedSize) ?                        m_sizeFloating.cy = m_sizeDocked.cy = nLength :                        m_sizeFloating.cy = nLength);        else           return CSize((m_bChangeDockedSize) ?                        m_sizeFloating.cx = m_sizeDocked.cx = nLength :                        m_sizeFloating.cx = nLength, m_sizeFloating.cy);   }   BEGIN_MESSAGE_MAP(CResizableDlgBar, CDialogBar)       //<AngularNoBind>{{</AngularNoBind>AFX_MSG_MAP(CResizableDlgBar)           // NOTE - the ClassWizard will add and remove mapping macroshere.       //<AngularNoBind>}}</AngularNoBind>AFX_MSG_MAP   END_MESSAGE_MAP()   /////////////////////////////////////////////////////////////////////    // CResizableDlgBar message handlers   ///////////////////////////////////////////////////////////////////// 				
REFERENCES
MFC Technical Note 31.