Creating Custom Explorer Bars, Tool Bands, and Desk Bands

The Explorer Bar was introduced with Microsoft Internet Explorer 4.0 to provide a display area adjacent to the browser pane. It is basically a child window within the Internet Explorer window, and it can be used to display information and interact with the user in much the same way. Explorer Bars are most commonly displayed as a vertical pane on the left side of the browser pane. However, an Explorer Bar can also be displayed horizontally, below the browser pane.

There is a wide range of possible uses for the Explorer Bar. Users can select which option they want to see in several different ways, including selecting it from the Explorer Bar submenu of the View menu, or clicking a toolbar button. Internet Explorer provides several standard Explorer Bars, including Favorites and Search.

One of the ways you can customize Internet Explorer is by adding a custom Explorer Bar. When implemented and registered, it will be added to the Explorer Bar submenu of the View menu. When selected by the user, the Explorer Bar's display area can then be used to display information and take user input in much the same way as a normal window.

To create a custom Explorer Bar, you must implement and register a band object. Band objects were introduced with version 4.71 of the Shell and provide capabilities similar to those of normal windows. However, because they are Component Object Model (COM) objects and contained by either Internet Explorer or the Shell, they are implemented somewhat differently. Simple band objects were used to create the sample Explorer Bars displayed in the first graphic. The implementation of the vertical Explorer Bar sample will be discussed in detail in a later section.

The following topics are discussed.

• Tool Bands
• Desk Bands
• Implementing Band Objects

Tool Bands

A tool band is a band object that was introduced with Internet Explorer 5 to support the Microsoft Windows radio toolbar feature. The Internet Explorer toolbar is actually a rebar control that contains several toolbar controls. By creating a tool band, you can add a band to that rebar control. However, like Explorer Bars, a tool band is a general purpose window.

Users display a toolbar by selecting it from the Toolbars submenu of the View menu or from the shortcut menu that is displayed by right-clicking the toolbar area.

Desk Bands

Band objects can also be used to create desk bands. While their basic implementation is similar to Explorer Bars, desk bands are unrelated to Internet Explorer. A desk band is basically a way to create a dockable window on the desktop. The user selects it by right-clicking the taskbar and selecting it from the Toolbars submenu.

Initially, desk bands are docked on the taskbar.

The user can then drag the desk band to the desktop, and it will appear as a normal window.

Implementing Band Objects

The following topics are discussed.

• Band Object Basics
• Band Registration
• A Simple Example of a Custom Explorer Bar

Band Object Basics

Although they can be used much like normal windows, band objects are COM objects that exist within a container. Explorer Bars are contained by Internet Explorer, and desk bands are contained by the Shell. While they serve different functions, their basic implementation is very similar. The primary difference is in how the band object is registered, which in turn controls the type of object and its container. This section discusses those aspects of implementation that are common to all band objects. See A Simple Example of a Custom Explorer Bar for additional implementation details.

In addition to IUnknown and IClassFactory, all band objects must implement the following interfaces.

• IDeskBand
• IObjectWithSite
• IPersistStream

In addition to registering their class identifier (CLSID), the Explorer Bar and desk band objects must also be registered for the appropriate component category. Registering the component category determines the object type and its container. Tool bands use a different registration procedure and do not have a category identifier (CATID). The CATIDs for the three band objects that require them are:

Band Type	Component Category
Vertical Explorer Bar	CATID_InfoBand
Horizontal Explorer Bar	CATID_CommBand
Desk Band	CATID_DeskBand

See Band Registration for further discussion of how to register band objects.

If the band object is to accept user input, it must also implement IInputObject. To add items to the shortcut menu for Explorer Bar or desk bands, the band object must export IContextMenu. Tool bands do not support shortcut menus.

Because band objects implement a child window, they must also implement a window procedure to handle Windows messaging.

Band objects can send commands to their container through the container's IOleCommandTarget interface. To obtain the interface pointer, call the container's IInputObjectSite::QueryInterface method and ask for IID_IOleCommandTarget. You then send commands to the container with IOleCommandTarget::Exec. The command group is CGID_DeskBand. When a band object's err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\] method is called, the container uses the dwBandID parameter to assign the band object an identifier that is used for three of the commands. Four IOleCommandTarget::Exec command IDs are supported.

• DBID_BANDINFOCHANGED

  The band's information has changed. Set the pvaIn parameter to the band identifier that was received in the most recent call to err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\]. The container will call the band object's err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\] method to request the updated information.

• DBID_MAXIMIZEBAND

  Maximize the band. Set the pvaIn parameter to the band identifier that was received in the most recent call to err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\].

• DBID_SHOWONLY

  Turn other bands in the container on or off. Set the pvaIn parameter to the VT_UNKNOWN type with one of the following values:

  Value	Description
  pUnk	A pointer to the band object's IUnknown interface. All other desk bands will be hidden.
  0	Hide all desk bands.
  1	Show all desk bands.

• DBID_PUSHCHEVRON

  Version 5. Display a chevron menu. The container sends an RB_PUSHCHEVRON message, and the band object receives an RBN_CHEVRONPUSHED notification that prompts it to display the chevron menu. Set the IOleCommandTarget::Exec method's nCmdExecOpt parameter to the band identifier received in the most recent call to err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\]. Set the IOleCommandTarget::Exec method's pvaIn parameter to the VT_I4 type with an application-defined value. It passes back to the band object as the lAppValue value of the RBN_CHEVRONPUSHED notification.

Band Registration

A band object must be registered as an OLE in-process server that supports apartment threading. The default value for the server is a menu text string. For Explorer Bars, it will appear in the Explorer Bar submenu of the Internet Explorer View menu. For tool bands, it will appear in the Toolbars submenu of the Internet Explorer View menu. For desk bands, it will appear in the Toolbars submenu of the taskbar's shortcut menu. As with menu resources, placing an ampersand (&) in front of a letter will cause it to be underlined and enable keyboard shortcuts. For example, the menu string for the vertical Explorer Bar shown in the first graphic is "Sample &Vertical Explorer Bar".

In general, the basic registry entry for a band object will appear as follows.

HKEY_CLASSES_ROOT

CLSID

{Your Band Object's CLSID GUID}

(Default) = Menu Text String

• InProcServer32

Tool bands must also have their object's CLSID registered with Internet Explorer. To do this, assign a value under HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Toolbar named with the tool band object's CLSID GUID as shown here. Its data value is ignored, so the value type is unimportant.

HKEY_LOCAL_MACHINE

Software

Microsoft

Internet Explorer

• Toolbar

There are several optional values that can also be added to the registry. For instance, the following value is necessary if you want to use the Explorer Bar to display HTML The value shown is not an example, but the actual value that should be used.

HKEY_CLASSES_ROOT

CLSID

{Your Band Object's CLSID GUID}

Instance

• CLSID

Used in conjunction with the value shown above, the following optional value is also necessary if you want to use the Explorer Bar to display HTML. This value should be set to the location of the file that contains the HTML content for the Explorer Bar.

HKEY_CLASSES_ROOT

CLSID

{Your Band Object's CLSID GUID}

Instance

• InitPropertyBag

Another optional value defines the default width or height of the Explorer Bar, depending on whether it is vertical or horizontal, respectively.

HKEY_CURRENT_USER

Software

Microsoft

Internet Explorer

Explorer Bars

• {Your Band Object's CLSID GUID}

The BarSize value should be set to the width or height of the bar. The value requires eight bytes and is placed in the registry as a binary value. The first four bytes specify the size in pixels, in hexadecimal format, starting from the leftmost byte. The last four bytes are reserved and should be set to zero.

As an example, the full registry entries for an HTML-capable Explorer Bar with a default width of 291 (0x123) pixels are shown here.

HKEY_CLASSES_ROOT

CLSID

{Your Band Object's CLSID GUID}

(Default) = Menu Text String

• InProcServer32

Instance

• CLSID

• InitPropertyBag

HKEY_CURRENT_USER

Software

Microsoft

Internet Explorer

Explorer Bars

• {Your Band Object's CLSID GUID}

You can handle registration of a band object's CATID programmatically. Create a component categories manager object (CLSID_StdComponentCategoriesMgr) and request a pointer to its ICatRegister interface. Pass the band object's CLSID and CATID to ICatRegister::RegisterClassImplCategories.

A Simple Example of a Custom Explorer Bar

This example goes through the implementation of the sample vertical Explorer Bar shown in the introduction. The complete source code, which also implements a horizontal Explorer Bar and a desk band, is included here for reference.

The basic procedure for creating a custom Explorer Bar is as follows.

1. Implement the functions needed by the DLL.
2. Implement the required COM interfaces.
3. Implement any desired optional COM interfaces.
4. Register the object's CLSID and, if required, component category.
5. Create a child window of Internet Explorer, sized to fit the Explorer Bar's display region.
6. Use the child window to display information and interact with the user.

The very simple implementation used in the Explorer Bar sample could actually be used for either type of Explorer Bar, or a desk band, by simply registering it for the appropriate component category. More sophisticated implementations will need to be customized for each object type's display region and container. However, much of this customization can be accomplished by taking the sample code and extending it by applying familiar Windows programming techniques to the child window. For example, you can add controls for user interaction, or graphics for a richer display.

DLL Functions

All three objects are packaged in a single DLL, which exposes the following functions.

• DllMain
• DllCanUnloadNow
• DllGetClassObject
• DllRegisterServer

The first three functions are standard implementations and will not be discussed here. The Class Factory implementation is also standard.

Required Interface Implementations

The vertical Explorer Bar sample implements the four required interfaces: IUnknown, IObjectWithSite, IPersistStream, and IDeskBand as part of the CExplorerBar class. The constructor, destructor, and IUnknown implementations are straightforward, and will not be discussed here. See the sample code for details.

The following interfaces are discussed in detail.

• IObjectWithSite
• IPersistStream
• IDeskBand

IObjectWithSite

When the user selects an Explorer Bar, the container calls the corresponding band object's IObjectWithSite::SetSite method. The punkSite parameter will be set to the site's IUnknown pointer.

In general, a SetSite implementation should perform the following steps:

1. Release any site pointer that is currently being held.
2. If the pointer passed to SetSite is set to NULL, the band is being removed. SetSite can return S_OK.
3. If the pointer passed to SetSite is non-NULL, a new site is being set. SetSite should do the following:
   1. Call QueryInterface on the site for its IOleWindow interface.
   2. Call IOleWindow::GetWindow to obtain the parent window's handle. Save the handle for later use. Release IOleWindow if it is no longer needed.
   3. Create the band object's window as a child of the window obtained in the previous step. Do not create it as a visible window.
   4. If the band object implements IInputObject, call QueryInterface on the site for its IInputObjectSite interface. Store the pointer to this interface for use later.
   5. If all steps are successful, return S_OK. If not, return the OLE-defined error code indicating what failed.

The Explorer Bar sample implements SetSite in the following way. In the following code m_pSite is a private member variable that holds the IInputObjectSite pointer and m_hwndParent holds the parent window's handle.

STDMETHODIMP CExplorerBar::SetSite(IUnknown *punkSite)
{
    //If a site is being held, release it.
    if(m_pSite)
    {
        m_pSite->Release();
        m_pSite = NULL;
    }

    //If punkSite is not NULL, a new site is being set.
    if(punkSite)
    {
        //Get the parent window.
        IOleWindow  *pOleWindow;

        m_hwndParent = NULL;

        if(SUCCEEDED(punkSite->QueryInterface(IID_IOleWindow, 
                     (LPVOID*)&pOleWindow)))
        {
            pOleWindow->GetWindow(&m_hwndParent);
            pOleWindow->Release();
        }

        if(!m_hwndParent)
            return E_FAIL;

        if(!RegisterAndCreateWindow())
            return E_FAIL;

        //Get and keep the IInputObjectSite pointer.
        if(SUCCEEDED(punkSite->QueryInterface(IID_IInputObjectSite, 
                     (LPVOID*)&m_pSite)))
        {
            return S_OK;
        }  

        return E_FAIL;
    }

    return S_OK;
}

The sample's GetSite implementation simply wraps a call to the site's QueryInterface method, using the site pointer saved by SetSite.

STDMETHODIMP CExplorerBar::GetSite(REFIID riid, LPVOID *ppvReturn)
{
    *ppvReturn = NULL;

    if(m_pSite)
        return m_pSite->QueryInterface(riid, ppvReturn);

    return E_FAIL;
}

Window creation is handled by the private RegisterAndCreateWindow method. If the window does not exist, this method creates the Explorer Bar's window as an appropriately sized child of the parent window obtained by SetSite. The child window's handle is stored in m_hwnd.

BOOL CExplorerBar::RegisterAndCreateWindow(void)
{
    //If the window doesn't exist yet, create it now.
    if(!m_hWnd)
    {
        //Can't create a child window without a parent.
        if(!m_hwndParent)
        {
            return FALSE;
        }

        //If the window class has not been registered, then do so.
        WNDCLASS wc;
        
        if(!GetClassInfo(g_hInst, EB_CLASS_NAME, &wc))
        {
            ZeroMemory(&wc, sizeof(wc));
            wc.style          = CS_HREDRAW | CS_VREDRAW | CS_GLOBALCLASS;
            wc.lpfnWndProc    = (WNDPROC)WndProc;
            wc.cbClsExtra     = 0;
            wc.cbWndExtra     = 0;
            wc.hInstance      = g_hInst;
            wc.hIcon          = NULL;
            wc.hCursor        = LoadCursor(NULL, IDC_ARROW);
            wc.hbrBackground  = (HBRUSH)CreateSolidBrush(RGB(0, 0, 192));
            wc.lpszMenuName   = NULL;
            wc.lpszClassName  = EB_CLASS_NAME;
  
            if(!RegisterClass(&wc))
            {
                //If RegisterClass fails, CreateWindow below will fail.
            }
        }

        RECT  rc;

        GetClientRect(m_hwndParent, &rc);

        //Create the window. The WndProc will set m_hWnd.
        CreateWindowEx(0,
                       EB_CLASS_NAME,
                       NULL,
                       WS_CHILD | WS_CLIPSIBLINGS | WS_BORDER,
                       rc.left,
                       rc.top,
                       rc.right - rc.left,
                       rc.bottom - rc.top,
                       m_hwndParent,
                       NULL,
                       g_hInst,
                       (LPVOID)this);
    }

    return (NULL != m_hWnd);
}

IPersistStream

Internet Explorer will call the Explorer Bar's IPersistStream interface to allow the Explorer Bar to load or save persistent data. If there is no persistent data, the methods must still return a success code. The IPersistStream interface inherits from IPersist, so five methods must be implemented.

• IPersist::GetClassID
• IPersistStream::IsDirty
• IPersistStream::Load
• IPersistStream::Save
• IPersistStream::GetSizeMax

The Explorer Bar sample does not use any persistent data and has only a minimal implementation of IPersistStream. IPersist::GetClassID returns the object's CLSID (CLSID_SampleExplorerBar), and the remainder return either S_OK, S_FALSE, or E_NOTIMPL.

IDeskBand

The IDeskBand interface is specific to band objects. In addition to its one method, it inherits from IDockingWindow, which in turn inherits from IOleWindow.

There are two IOleWindow methods: GetWindow and ContextSensitiveHelp. The Explorer Bar sample's implementation of GetWindow returns the Explorer Bar's child window handle, m_hwnd. Context-sensitive Help is not implemented, so IOleWindow::ContextSensitiveHelp returns E_NOTIMPL.

The IDockingWindow interface has three methods.

• IDockingWindow::ShowDW
• IDockingWindow::CloseDW
• IDockingWindow::ResizeBorderDW

The ResizeBorderDW method is not used with any type of band object and should always return E_NOTIMPL. The ShowDW method either shows or hides the Explorer Bar's window, depending on the value of its parameter.

STDMETHODIMP CExplorerBar::ShowDW(BOOL fShow)
{
    if(m_hWnd)
    {
        if(fShow)
        {
            //show our window
            ShowWindow(m_hWnd, SW_SHOW);
        }
        else
        {
            //hide our window
            ShowWindow(m_hWnd, SW_HIDE);
        }
    }

    return S_OK;
}

The CloseDW method destroys the Explorer Bar's window.

STDMETHODIMP CExplorerBar::CloseDW(DWORD dwReserved)
{
    ShowDW(FALSE);

    if(IsWindow(m_hWnd))
        DestroyWindow(m_hWnd);

    m_hWnd = NULL;

    return S_OK;
}

The remaining method, err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\], is specific to IDeskBand. Internet Explorer uses it to specify the Explorer Bar's identifier and viewing mode. Internet Explorer also may request one or more pieces of information from the Explorer Bar by filling the dwMask member of the DESKBANDINFO structure that is passed as the third parameter. err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\] should store the identifier and viewing mode and fill the DESKBANDINFO structure with the requested data. The Explorer Bar sample implements err! bad xref: _win32_IDeskBand_GetBandInfo [ambiguous xref; must specify @autoiid, @iid, or @primary.\] as shown in the following code example.

STDMETHODIMP CExplorerBar::GetBandInfo(DWORD dwBandID, DWORD dwViewMode, 
                                       DESKBANDINFO *pdbi)
{
    if(pdbi)
    {
        m_dwBandID = dwBandID;
        m_dwViewMode = dwViewMode;

        if(pdbi->dwMask & DBIM_MINSIZE)
        {
            pdbi->ptMinSize.x = MIN_SIZE_X;
            pdbi->ptMinSize.y = MIN_SIZE_Y;
        }

        if(pdbi->dwMask & DBIM_MAXSIZE)
        {
            pdbi->ptMaxSize.x = -1;
            pdbi->ptMaxSize.y = -1;
        }

        if(pdbi->dwMask & DBIM_INTEGRAL)
        {
            pdbi->ptIntegral.x = 1;
            pdbi->ptIntegral.y = 1;
        }

        if(pdbi->dwMask & DBIM_ACTUAL)
        {
            pdbi->ptActual.x = 0;
            pdbi->ptActual.y = 0;
        }

        if(pdbi->dwMask & DBIM_TITLE)
        {
            hr = StringCbCopyW(pdbi->wszTitle, sizeof(pdbi->wszTitle), L"Sample Explorer Bar");
            // TODO: Add error handling code here to check the hr return value.
        }

        if(pdbi->dwMask & DBIM_MODEFLAGS)
        {
            pdbi->dwModeFlags = DBIMF_VARIABLEHEIGHT;
        }

        if(pdbi->dwMask & DBIM_BKCOLOR)
        {
            //Use the default background color by removing this flag.
            pdbi->dwMask &= ~DBIM_BKCOLOR;
        }

        return S_OK;
    }

    return E_INVALIDARG;
}

Optional Interface Implementations

There are two interfaces that are not required, but that may be useful to implement: IInputObject and IContextMenu. The Explorer Bar sample implements IInputObject. Refer to the documentation for information on how to implement IContextMenu.

IInputObject

The IInputObject interface must be implemented if a band object accepts user input. Internet Explorer implements IInputObjectSite and uses IInputObject to maintain proper user input focus when it has more than one contained window. There are three methods that need to be implemented by an Explorer Bar.

• IInputObject::UIActivateIO
• IInputObject::HasFocusIO
• IInputObject::TranslateAcceleratorIO

Internet Explorer calls UIActivateIO to inform the Explorer Bar that it is being activated or deactivated. When activated, the Explorer Bar sample calls SetFocus to set the focus to its window.

Internet Explorer calls HasFocusIO when it is attempting to determine which window has focus. If the Explorer Bar's window or one of its descendants has focus, HasFocusIO should return S_OK. If not, it should return S_FALSE.

TranslateAcceleratorIO allows the object to process keyboard accelerators. The Explorer Bar sample does not implement this method, so it returns S_FALSE.

The sample bar's implementation of IInputObjectSite is as follows.

STDMETHODIMP CExplorerBar::UIActivateIO(BOOL fActivate, LPMSG pMsg)
{
    if(fActivate)
        SetFocus(m_hWnd);

    return S_OK;
}

STDMETHODIMP CExplorerBar::HasFocusIO(void)
{
    if(m_bFocus)
        return S_OK;

    return S_FALSE;
}

STDMETHODIMP CExplorerBar::TranslateAcceleratorIO(LPMSG pMsg)
{
    return S_FALSE;
}

CLSID Registration

As with all COM objects, the Explorer Bar's CLSID must be registered. For the object to function properly with Internet Explorer, it must also be registered for the appropriate component category (CATID_InfoBand). The relevant code section for the vertical Explorer Bar is shown in the following code example.

...

//Register the Explorer Bar object.
if(!RegisterServer(CLSID_SampleExplorerBar, 
                   TEXT("Sample &Vertical Explorer Bar")))
   return SELFREG_E_CLASS;

//Register the component categories for the Explorer Bar object.
if(!RegisterComCat(CLSID_SampleExplorerBar, CATID_InfoBand))
   return SELFREG_E_CLASS;

... 

Registration of band objects in the sample uses normal COM procedures and is handled by a private function, RegisterServer.

In addition to the CLSID, the band object server must also be registered for one or more component categories. This is actually the main difference in implementation between the vertical and horizontal Explorer Bar samples. This process is handled by creating a component categories manager object (CLSID_StdComponentCategoriesMgr) and using the ICatRegister::RegisterClassImplCategories method to register the band object server. In this example, component category registration is handled by passing the Explorer Bar sample's CLSID and CATID to a private function—RegisterComCat—as shown in the following code example.

BOOL RegisterComCat(CLSID clsid, CATID CatID)
{
    ICatRegister  *pcr;
    HRESULT        hr = S_OK ;

    CoInitialize(NULL);

    hr = CoCreateInstance(CLSID_StdComponentCategoriesMgr, 
                          NULL, 
                          CLSCTX_INPROC_SERVER, 
                          IID_ICatRegister, 
                          (LPVOID*)&pcr);

    if(SUCCEEDED(hr))
    {
        hr = pcr->RegisterClassImplCategories(clsid, 1, &CatID);
        pcr->Release();
    }

    CoUninitialize();

    return SUCCEEDED(hr);
}

The Window Procedure

Because a band object uses a child window for its display, it must implement a window procedure to handle Windows messaging. The band sample has minimal functionality, so its window procedure only handles five messages:

• WM_NCCREATE
• WM_PAINT
• WM_COMMAND
• WM_SETFOCUS
• WM_KILLFOCUS

The procedure can easily be expanded to accommodate additional messages to support more features.

LRESULT CALLBACK CExplorerBar::WndProc(HWND hWnd, UINT uMessage, WPARAM wParam, LPARAM lParam)
{
    CExplorerBar  *pThis = (CExplorerBar*)GetWindowLong(hWnd, GWL_USERDATA);

    switch (uMessage)
    {
        case WM_NCCREATE:
        {
            LPCREATESTRUCT lpcs = (LPCREATESTRUCT)lParam;
            pThis = (CExplorerBar*)(lpcs->lpCreateParams);
            SetWindowLong(hWnd, GWL_USERDATA, (LONG)pThis);

            //set the window handle
            pThis->m_hWnd = hWnd;
        }
        break;  

        case WM_PAINT:
            return pThis->OnPaint();  

        case WM_COMMAND:
            return pThis->OnCommand(wParam, lParam);  

        case WM_SETFOCUS:
            return pThis->OnSetFocus();

        case WM_KILLFOCUS:
            return pThis->OnKillFocus();
    }

    return DefWindowProc(hWnd, uMessage, wParam, lParam);
}

The WM_COMMAND handler simply returns zero. The WM_PAINT handler creates the simple text display shown in the Explorer Bar example in the introduction.

LRESULT CExplorerBar::OnPaint(void)
{
    PAINTSTRUCT ps;
    RECT        rc;

    BeginPaint(m_hWnd, &ps);
    GetClientRect(m_hWnd, &rc);
    SetTextColor(ps.hdc, RGB(255, 255, 255));
    SetBkMode(ps.hdc, TRANSPARENT);
    
    DrawText(ps.hdc, 
             TEXT("Sample Explorer Bar"), 
             -1, 
             &rc, 
             DT_SINGLELINE | DT_CENTER | DT_VCENTER);
             
    EndPaint(m_hWnd, &ps);

    return 0;
}

The WM_SETFOCUS and WM_KILLFOCUS handlers inform the site of a focus change by calling the site's IInputObjectSite::OnFocusChangeIS method.

LRESULT CExplorerBar::OnSetFocus(void)
{
    FocusChange(TRUE);

    return 0;
}

LRESULT CExplorerBar::OnKillFocus(void)
{
    FocusChange(FALSE);

    return 0;
}

void CExplorerBar::FocusChange(BOOL bFocus)
{
    m_bFocus = bFocus;

    //Inform the input object site that the focus has changed.
    if(m_pSite)
    {
        m_pSite->OnFocusChangeIS((IDockingWindow*)this, bFocus);
    }
}

Band objects provide a flexible and powerful way to extend the capabilities of Internet Explorer by creating custom Explorer Bars. Implementing a desk band enables you to extend the capabilities of normal windows. Although some COM programming is required, it ultimately serves to provide a child window for your user interface. From there, the bulk of the implementation can use familiar Windows programming techniques. While the example discussed here has only limited functionality, it illustrates all the necessary features of a band object and it can be readily extended to create a unique and powerful user interface.