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CScrollBar Class

  • Cikk

Provides the functionality of a Windows scroll-bar control.

Syntax

class CScrollBar : public CWnd

Members

Public Constructors

Name Description
CScrollBar::CScrollBar Constructs a CScrollBar object.

Public Methods

Name Description
CScrollBar::Create Creates the Windows scroll bar and attaches it to the CScrollBar object.
CScrollBar::EnableScrollBar Enables or disables one or both arrows of a scroll bar.
CScrollBar::GetScrollBarInfo Retrieves information about the scroll bar using a SCROLLBARINFO structure.
CScrollBar::GetScrollInfo Retrieves information about the scroll bar.
CScrollBar::GetScrollLimit Retrieves the limit of the scroll bar
CScrollBar::GetScrollPos Retrieves the current position of a scroll box.
CScrollBar::GetScrollRange Retrieves the current minimum and maximum scroll-bar positions for the given scroll bar.
CScrollBar::SetScrollInfo Sets information about the scroll bar.
CScrollBar::SetScrollPos Sets the current position of a scroll box.
CScrollBar::SetScrollRange Sets minimum and maximum position values for the given scroll bar.
CScrollBar::ShowScrollBar Shows or hides a scroll bar.

Remarks

You create a scroll-bar control in two steps. First, call the constructor CScrollBar to construct the CScrollBar object, then call the Create member function to create the Windows scroll-bar control and attach it to the CScrollBar object.

If you create a CScrollBar object within a dialog box (through a dialog resource), the CScrollBar is automatically destroyed when the user closes the dialog box.

If you create a CScrollBar object within a window, you may also need to destroy it.

If you create the CScrollBar object on the stack, it's destroyed automatically. If you create the CScrollBar object on the heap by using the new function, you must call delete on the object to destroy it when the user terminates the Windows scroll bar.

If you allocate any memory in the CScrollBar object, override the CScrollBar destructor to dispose of the allocations.

For related information about using CScrollBar, see Controls.

Inheritance Hierarchy

CObject

CCmdTarget

CWnd

CScrollBar

Requirements

Header: afxwin.h

CScrollBar::Create

Creates the Windows scroll bar and attaches it to the CScrollBar object.

virtual BOOL Create(
    DWORD dwStyle,
    const RECT& rect,
    CWnd* pParentWnd,
    UINT nID);

Parameters

dwStyle
Specifies the scroll bar's style. Apply any combination of scroll-bar styles to the scroll bar.

rect
Specifies the scroll bar's size and position. Can be either a RECT structure or a CRect object.

pParentWnd
Specifies the scroll bar's parent window, usually a CDialog object. It must not be NULL.

nID
The scroll bar's control ID.

Return Value

Nonzero if successful; otherwise 0.

Remarks

You construct a CScrollBar object in two steps. First, call the constructor, which constructs the CScrollBar object; then call Create, which creates and initializes the associated Windows scroll bar and attaches it to the CScrollBar object.

Apply the following window styles to a scroll bar:

  • WS_CHILD Always

  • WS_VISIBLE Usually

  • WS_DISABLED Rarely

  • WS_GROUP To group controls

Example

// Example 1:
// Create a horizontal CScrollBar control as a child window of CMyDialog
// class (a CDialog-derived class). The scroll bar is NOT visible until the
// call ShowScrollBar() is made. m_ScrollBarHorz is of type CScrollBar class,
// and it is a member variable in CMyDialog class.
VERIFY(m_ScrollBarHorz.Create(SBS_HORZ | SBS_TOPALIGN | WS_CHILD,
                              CRect(5, 5, 100, 30), this, IDC_SCROLLBARCTRL));

m_ScrollBarHorz.ShowScrollBar();

// Example 2:
// Create a vertical CScrollBar control as a child window of CMyDialog
// class (a CDialog-derived class). m_ScrollBarVert is of type CScrollBar
// class, and it is a member variable in CMyDialog class.
VERIFY(m_ScrollBarVert.Create(SBS_VERT | SBS_LEFTALIGN | WS_CHILD |
                                  WS_VISIBLE,
                              CRect(5, 30, 30, 130), this, IDC_SCROLLBARCTRL));

CScrollBar::CScrollBar

Constructs a CScrollBar object.

CScrollBar();

Remarks

After constructing the object, call the Create member function to create and initialize the Windows scroll bar.

Example

CScrollBar m_ScrollBarHorz;

CScrollBar::EnableScrollBar

Enables or disables one or both arrows of a scroll bar.

BOOL EnableScrollBar(UINT nArrowFlags = ESB_ENABLE_BOTH);

Parameters

nArrowFlags
Specifies whether the scroll arrows are enabled or disabled and which arrows are enabled or disabled. This parameter can be one of the following values:

  • ESB_ENABLE_BOTH Enables both arrows of a scroll bar.

  • ESB_DISABLE_LTUP Disables the left arrow of a horizontal scroll bar or the up arrow of a vertical scroll bar.

  • ESB_DISABLE_RTDN Disables the right arrow of a horizontal scroll bar or the down arrow of a vertical scroll bar.

  • ESB_DISABLE_BOTH Disables both arrows of a scroll bar.

Return Value

Nonzero if the arrows are enabled or disabled as specified; otherwise 0, which indicates that the arrows are already in the requested state or that an error occurred.

Example

See the example for CScrollBar::SetScrollRange.

CScrollBar::GetScrollBarInfo

Retrieves the information that the SCROLLBARINFO structure maintains about a scroll bar.

BOOL GetScrollBarInfo(PSCROLLBARINFO pScrollInfo) const;

Parameters

pScrollInfo
A pointer to the SCROLLBARINFO structure.

Return Value

Returns TRUE on success, FALSE on failure.

Remarks

This member function emulates the functionality of the SBM_SCROLLBARINFO message, as described in the Windows SDK.

CScrollBar::GetScrollInfo

Retrieves the information that the SCROLLINFO structure maintains about a scroll bar.

BOOL GetScrollInfo(
    LPSCROLLINFO lpScrollInfo,
    UINT nMask = SIF_ALL);

Parameters

lpScrollInfo
A pointer to a SCROLLINFO structure. See the Windows SDK for more information about this structure.

nMask
Specifies the scroll bar parameters to retrieve. Typical usage, SIF_ALL, specifies a combination of SIF_PAGE, SIF_POS, SIF_TRACKPOS, and SIF_RANGE. See SCROLLINFO for more information on the nMask values.

Return Value

If the message retrieved any values, the return is TRUE. Otherwise, it's FALSE.

Remarks

GetScrollInfo enables applications to use 32-bit scroll positions.

The SCROLLINFO structure contains information about a scroll bar, including the minimum and maximum scrolling positions, the page size, and the position of the scroll box (the thumb). See the SCROLLINFO structure topic in the Windows SDK for more information about changing the structure defaults.

The MFC Windows message handlers that indicate scroll bar position, CWnd::OnHScroll, and CWnd::OnVScroll, provide only 16 bits of position data. GetScrollInfo and SetScrollInfo provide 32 bits of scroll bar position data. Thus, an application can call GetScrollInfo while processing either CWnd::OnHScroll or CWnd::OnVScroll to obtain 32-bit scroll bar position data.

Example

See the example for CWnd::OnHScroll.

CScrollBar::GetScrollLimit

Retrieves the maximum scrolling position of the scroll bar.

int GetScrollLimit();

Return Value

Specifies the maximum position of a scroll bar if successful; otherwise 0.

Example

See the example for CWnd::OnHScroll.

CScrollBar::GetScrollPos

Retrieves the current position of a scroll box.

int GetScrollPos() const;

Return Value

Specifies the current position of the scroll box if successful; otherwise 0.

Remarks

The current position is a relative value that depends on the current scrolling range. For example, if the scrolling range is 100 to 200 and the scroll box is in the middle of the bar, the current position is 150.

Example

See the example for CWnd::OnHScroll.

CScrollBar::GetScrollRange

Copies the current minimum and maximum scroll-bar positions for the given scroll bar to the locations specified by lpMinPos and lpMaxPos.

void GetScrollRange(
    LPINT lpMinPos,
    LPINT lpMaxPos) const;

Parameters

lpMinPos
Points to the integer variable that is to receive the minimum position.

lpMaxPos
Points to the integer variable that is to receive the maximum position.

Remarks

The default range for a scroll-bar control is empty (both values are 0).

Example

See the example for CWnd::OnHScroll.

CScrollBar::SetScrollInfo

Sets the information that the SCROLLINFO structure maintains about a scroll bar.

BOOL SetScrollInfo(
    LPSCROLLINFO lpScrollInfo,
    BOOL bRedraw = TRUE);

Parameters

lpScrollInfo
A pointer to a SCROLLINFO structure.

bRedraw
Specifies whether the scroll bar should be redrawn to reflect the new information. If bRedraw is TRUE, the scroll bar is redrawn. If it's FALSE, it isn't redrawn. The scroll bar is redrawn by default.

Return Value

If successful, the return is TRUE. Otherwise, it's FALSE.

Remarks

You must provide the values required by the SCROLLINFO structure parameters, including the flag values.

The SCROLLINFO structure contains information about a scroll bar, including the minimum and maximum scrolling positions, the page size, and the position of the scroll box (the thumb). See the SCROLLINFO structure topic in the Windows SDK for more information about changing the structure defaults.

Example

// Set SCROLLINFO for the scroll bar. m_ScrollBarHorz is of type
// CScrollBar class, and it is a member variable in CMyDialog class.
SCROLLINFO info;
info.cbSize = sizeof(SCROLLINFO);
info.fMask = SIF_ALL;
info.nMin = 0;
info.nMax = 10;
info.nPage = 2;
info.nPos = 5;
info.nTrackPos = 2;
m_ScrollBarHorz.SetScrollInfo(&info);

CScrollBar::SetScrollPos

Sets the current position of a scroll box to that specified by nPos and, if specified, redraws the scroll bar to reflect the new position.

int SetScrollPos(
    int nPos,
    BOOL bRedraw = TRUE);

Parameters

nPos
Specifies the new position for the scroll box. It must be within the scrolling range.

bRedraw
Specifies whether the scroll bar should be redrawn to reflect the new position. If bRedraw is TRUE, the scroll bar is redrawn. If it's FALSE, it isn't redrawn. The scroll bar is redrawn by default.

Return Value

Specifies the previous position of the scroll box if successful; otherwise 0.

Remarks

Set bRedraw to FALSE whenever the scroll bar will be redrawn by a subsequent call to another function to avoid having the scroll bar redrawn twice within a short interval.

Example

See the example for CScrollBar::SetScrollRange.

CScrollBar::SetScrollRange

Sets minimum and maximum position values for the given scroll bar.

void SetScrollRange(
    int nMinPos,
    int nMaxPos,
    BOOL bRedraw = TRUE);

Parameters

nMinPos
Specifies the minimum scrolling position.

nMaxPos
Specifies the maximum scrolling position.

bRedraw
Specifies whether the scroll bar should be redrawn to reflect the change. If bRedraw is TRUE, the scroll bar is redrawn; if FALSE, it isn't redrawn. It's redrawn by default.

Remarks

Set nMinPos and nMaxPos to 0 to hide standard scroll bars.

Don't call this function to hide a scroll bar while processing a scroll-bar notification message.

If a call to SetScrollRange immediately follows a call to the SetScrollPos member function, set bRedraw in SetScrollPos to 0 to prevent the scroll bar from being redrawn twice.

The difference between the values specified by nMinPos and nMaxPos must not be greater than 32,767. The default range for a scroll-bar control is empty (both nMinPos and nMaxPos are 0).

Example

// Sets minimum (0) and maximum (10) position values for the
// CScrollBar control. m_ScrollBarVert is of type CScrollBar class,
// and it is a member variable in CMyDialog class.
m_ScrollBarVert.SetScrollRange(0, 10);

// Set the position of the scroll box.
m_ScrollBarVert.SetScrollPos(5);

// Disable the down arrow of the scroll bar. By default, both arrows
// are enabled.
m_ScrollBarVert.EnableScrollBar(ESB_DISABLE_DOWN);

CScrollBar::ShowScrollBar

Shows or hides a scroll bar.

void ShowScrollBar(BOOL bShow = TRUE);

Parameters

bShow
Specifies whether the scroll bar is shown or hidden. If this parameter is TRUE, the scroll bar is shown; otherwise it's hidden.

Remarks

An application shouldn't call this function to hide a scroll bar while processing a scroll-bar notification message.

Example

See the example for CScrollBar::Create.

See also

CWnd Class
Hierarchy Chart
CButton Class
CComboBox Class
CEdit Class
CListBox Class
CStatic Class
CDialog Class