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Docking Mechanism Explained

The article describes how Prof-UIS implements the dockable control bar mechanism. It also explains the most important operations on the dockable control bar including how its position is set in a frame window.

Important terms

There are several terms that may have different meanings to different people. Brief descriptions of some important terms are given below.

Frame window
An overlapped/popup window with one child window in the center area and a set of child windows (control bars) that can be fixed to its borders.
Docking site
A popup frame window that contains a set of control bars in its either docked or floating state.
Floating container (floating palette, floating frame, mini frame)
A special kind of the frame window that encloses only one child docking bar window with the AFX_IDW_DOCKBAR_FLOAT dialog control identifier. The docking bar window encloses one or more control bars. Floating containers are created and destroyed automatically with the control bar’s drag-and-drop algorithm.
Control bar
The generalized MFC implementation of the window that can be either fixed to any of the borders of its parent frame window or floated in the floating container.
Fixed-size control bar
A fixed-size control bar (e.g. toolbars or menu bars). The size of the fixed bar in its docked state could not be changed by dragging its borders.
Resizable control bar *
A control bar that can be resized by dragging its borders and docked in the dynamic control bar containers.
Docking bar
A kind of an MFC control bar which is used as a parent window for all the control bars with the re-docking feature turned on (CControlBar::EnableDocking() is used for this). Basically MFC provides two types of docking bars, which are implemented as the internal class (CDockBar): floating bar (with the dialog control identifier set to AFX_IDW_DOCKBAR_FLOAT) and docking bar fixed to the sides of the docking site (with the dialog control identifiers set to AFX_IDW_DOCKBAR_LEFT, AFX_IDW_DOCKBAR_RIGHT, AFX_IDW_DOCKBAR_TOP, or AFX_IDW_DOCKBAR_BOTTOM). MFC supports only four docking bars for one docking site at the time (these bars are marked with red in the below). In Prof-UIS these bars are called "circle 0" or "outer docking bar circle". Both fixed and resizable bars can be docked into "circle 0", but the drag-and-drop algorithm for resizable bars docks them only into the Prof-UIS-specific inner docking bar "circles" with numbers starting from 1. In the figure below, "circle 1" is marked with blue, "circle 2" - with green. Inner circles are created and destroyed dynamically with the drag-and-drop algorithm for the resizable bar. These inner circles "allow" resizable bars to be docked to each other in a nested way. The fixed-size control bars could be docked only into "circle 0" marked with red.

Docking site’s client area
The area that is free of any bars. It is marked with yellow in the figure and used by MDI client windows in MDI applications and the view window in SDI applications.
Dynamic control bar container *
A special kind of the resizable control bar, which is created dynamically and used for docking other resizable bars to horizontal rows inside vertical rows and vice versa. The dynamic control bar container like any resizable control bar can take up part of the docking site or part of the floating container.
Status bar
The MFC implementation of the status line. The status bar cannot be re-docked by dragging any its area. It takes up part of the docking site under the lowest docking bar (i.e. under the red "circle 0").

* Prof-UIS - specific term

How to dock fixed-size control bars relatively each other?

To set a certain fixed docking bar location, just call your CMainFrame::DockControlBar() method with the appropriate parameter values. The following example arranges two toolbars into one horizontal image at the bottom of a frame window:


    CRect wrAlreadyDockedToolBar;
    m_wndToolBar1.GetWindowRect( &wrAlreadyDockedToolBar );
    wrAlreadyDockedToolBar.OffsetRect( 0, 1 );

How to dock resizable bars relatively each other?

Use the CExtControlBar::DockControlBar() methods (two overloaded functions) to set the relative positions of the control bars. In the sample below, the first method docks the m_wndResourceViewBar resizable bar to the newly created row in the left part of "docking circle 1". The second one is applied to the already docked m_wndResourceViewBar bar, with its parameters specifying the position of the m_wndServerExplorerBar bar relatively to the m_wndResourceViewBar one.


How to show or hide docked or floating control bars?

To make both fixed-size bars and resizable bars visible/invisible, the CFrameWnd::ShowControlBar() method should be used. The CControlBar::ShowWindow() cannot be used here, because it does not affect the positions of other bars in the same frame window (i.e. the method does not perform the frame layout recalculation).

How to float fixed-size bar?

For this purpose, use either CExtControlBar::FloatControlBar(), or CFrameWnd::FloatControlBar(). Both methods produce the same results.

How to float resizable bar?

The CExtControlBar::FloatControlBar() method should be used. The CFrameWnd::FloatControlBar() method is not allowed.

How to enable control bars in the docking site to be re-dockable?

Usually all the control bars (but the status bar) in any docking site are enabled to be re-dockable. This feature is turned on by performing the following two steps. First, call the static CExtControlBar::FrameEnableDocking( pDockSite ) method. Second, invoke the CExtControlBar::EnableDocking() method of the bar.

If a bar is not re-dockable, its parent window is the docking site. In case of a dockable bar, the parent window is always a docking bar window (even for a floating palette).

IMPORTANT: CExtControlBar::FrameEnableDocking( pDockSite ) should be used instead of CFrameWnd::EnableDocking().

How to activate resizable bar that is not visible?

The call of the static

method activates the resizable bar being in any state.

How to set initial size for resizable control bar?

Use the three methods below to initialize the desired size of a bar that is either in the docked state (vertical/horizontal) or in the floating state:

  • SetInitDesiredSizeVertical( CSize )
  • SetInitDesiredSizeHorizontal( CSize )
  • SetInitDesiredSizeFloating( CSize )

The real sizes of docked bars are adjusted proportionally between all the resizable bars in one row.

Please note that the bar can be in the floating state only when it itself is the single bar in its floating container. In any other case, the bar is in the docked state.

How to detect whether bar is in floating container or in docking site?

Call the CExtControlBar::GetParentFrame() method to get the pointer to the parent CFrameWnd-based window. If this returned object is kind of CMiniFrameWnd, the bar is docked inside a floating container. Otherwise the bar is docked in the docking site.

How to detect whether bar is visible or not?

Retrieve the bar window style flags by calling the GetStyle() method. The bar window is visible if its window style flags have the WS_VISIBLE flag. The CControlBar::IsVisible() method can additionally detect whether the bar is temporarily invisible.

How to handle control bar’s show/hide commands and update their associated command states in docking site?

These commands make each control bar visible/invisible. They are usually marked with check marks, which indicates visibility of the bars. Every docking bar has its own unique dialog control identifier and the corresponding menu command in the docking site. In this case, the context menu with the list of all the docking bars can be activated on every frame point. So, to set the correct check mark for the "Show/Hide" command of the bar, you should add the following two lines to the frame’s message map:

ON_COMMAND_EX( ID_BAR_... , OnBarCheck )
ON_UPDATE_COMMAND_UI( ID_BAR_... , OnUpdateControlBarMenu )

How to handle control bar’s show/hide commands and update their associated command states in docking site like in Visual Studio .NET?

First, see the previous answer. The difference is in the command handling/updating for the resizable bars. These commands have no check marks and are only used to activate resizable control bars. They never hide bars. Implement the new OnBarCheck() and OnUpdateControlBarMenu() methods in the docking site:

BOOL CMainFrame::OnBarCheck( UINT nID )

void CMainFrame::OnUpdateControlBarMenu( CCmdUI * pCmdUI )

How to load/save state of docking bars?

The state persistence is usually implemented in your CMainFrame’s OnCreate() and DestroyWindow() methods.

To load bars’ state:

    this, // some kind of CFrameWnd
    pApp->m_pszRegistryKey, // application registry key (usually company name)
    pApp->m_pszProfileName, // application profile name (usually product name)
    pApp->m_pszProfileName  // Prof-UIS profile name

To save bars’ state:

    this,  // some kind of CFrameWnd
    pApp->m_pszRegistryKey, // application registry key (usually company name)
    pApp->m_pszProfileName, // application profile name (usually product name)
    pApp->m_pszProfileName  // Prof-UIS profile name

How to add Visual Studio .NET like resizable control bar to frame window?

You should add the CExtControlBar member in the frame window class declaration. Creating a resizable control bar is similar to that of toolbar.

How to insert window into resizable control bar?

When creating such a child window, pass a pointer to CExtControlBar instance in the "parent window" parameter to the child window Create() method. After that, the control bar will automatically adjust the child window to its client area. So far, the resizable control bar allows only one child window

How to add docking menu bar to frame window?

The docking menu bar is implemented just as an ordinary toolbar. Any needed initialization should be performed in your CMainFrame’s OnCreate() handler. Moreover, you need to add a frame window class member of CExtMenuControlBar class.

if( !m_wndMenuBar.Create(
        _T( "Menubar name" ),
     !m_wndMenuBar.LoadMenuBar( IDR_MAINFRAME )
    TRACE0( _T( "Failed to create menubar\n" ) );
    return -1;


m_wndMenuBar.EnableDocking( CBRS_ALIGN_ANY );


CExtControlBar::FrameEnableDocking( this );


DockControlBar( &m_wndMenuBar );


By default, CExtMenuControlBar does not activate menu on pressing the ALT key. To enable this, you should override the PreTranslateMessage() virtual function in a frame window class and add the following lines before the parent PreTranslateMessage():

    if( m_wndMenuBar.TranslateMainFrameMessage( pMsg ) )
        return TRUE;

In the case of MDI, repeat the same in the child frame window class.

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