CScrollView Class

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A CView with scrolling capabilities.

Syntax

class CScrollView : public CView  

Members

Protected Constructors

Public Methods

Remarks

You can handle standard scrolling yourself in any class derived from CView by overriding the message-mapped OnHScroll and OnVScroll member functions. But CScrollView adds the following features to its CView capabilities:

• It manages window and viewport sizes and mapping modes.

• It scrolls automatically in response to scroll-bar messages.

• It scrolls automatically in response to messages from the keyboard, a non-scrolling mouse, or the IntelliMouse wheel.

To scroll automatically in response to messages from the keyboard, add a WM_KEYDOWN message, and test for VK_DOWN, VK_PREV and call SetScrollPos.

You can handle mouse wheel scrolling yourself by overriding the message-mapped OnMouseWheel and OnRegisteredMouseWheel member functions. As they are for CScrollView, these member functions support the recommended behaviour for WM_MOUSEWHEEL, the wheel rotation message.

To take advantage of automatic scrolling, derive your view class from CScrollView instead of from CView. When the view is first created, if you want to calculate the size of the scrollable view based on the size of the document, call the SetScrollSizes member function from your override of either CView::OnInitialUpdate or CView::OnUpdate. (You must write your own code to query the size of the document. For an example, see the Scribble sample.)

The call to the SetScrollSizes member function sets the view's mapping mode, the total dimensions of the scroll view, and the amounts to scroll horizontally and vertically. All sizes are in logical units. The logical size of the view is usually calculated from data stored in the document, but in some cases you may want to specify a fixed size. For examples of both approaches, see CScrollView::SetScrollSizes.

You specify the amounts to scroll horizontally and vertically in logical units. By default, if the user clicks a scroll bar shaft outside of the scroll box, CScrollView scrolls a "page." If the user clicks a scroll arrow at either end of a scroll bar, CScrollView scrolls a "line." By default, a page is 1/10 of the total size of the view; a line is 1/10 of the page size. Override these default values by passing custom sizes in the SetScrollSizes member function. For example, you might set the horizontal size to some fraction of the width of the total size and the vertical size to the height of a line in the current font.

Instead of scrolling, CScrollView can automatically scale the view to the current window size. In this mode, the view has no scroll bars and the logical view is stretched or shrunk to exactly fit the window's client area. To use this scale-to-fit capability, call CScrollView::SetScaleToFitSize. (Call either SetScaleToFitSize or SetScrollSizes, but not both.)

Before the OnDraw member function of your derived view class is called, CScrollView automatically adjusts the viewport origin for the CPaintDC device-context object that it passes to OnDraw.

To adjust the viewport origin for the scrolling window, CScrollView overrides CView::OnPrepareDC. This adjustment is automatic for the CPaintDC device context that CScrollView passes to OnDraw, but you must call CScrollView::OnPrepareDC yourself for any other device contexts you use, such as a CClientDC. You can override CScrollView::OnPrepareDC to set the pen, background color, and other drawing attributes, but call the base class to do scaling.

Scroll bars can appear in three places relative to a view, as shown in the following cases:

• Standard window-style scroll bars can be set for the view using the WS_HSCROLL and WS_VSCROLLWindows Styles.

• Scroll-bar controls can also be added to the frame containing the view, in which case the framework forwards WM_HSCROLL and WM_VSCROLL messages from the frame window to the currently active view.

• The framework also forwards scroll messages from a CSplitterWnd splitter control to the currently active splitter pane (a view). When placed in a CSplitterWnd with shared scroll bars, a CScrollView object will use the shared ones rather than creating its own.

For more information on using CScrollView, see Document/View Architecture and Derived View Classes Available in MFC.

Inheritance Hierarchy

CObject

CCmdTarget

CWnd

CView

CScrollView

Requirements

Header: afxwin.h

CScrollView::CheckScrollBars

Call this member function to determine if the scroll view has horizontal and vertical bars.

void CheckScrollBars(
    BOOL& bHasHorzBar,  
    BOOL& bHasVertBar) const;  

Parameters

bHasHorzBar
Indicates the application has a horizontal scroll bar.

bHasVertBar
Indicates the application has a vertical scroll bar.

CScrollView::CScrollView

Constructs a CScrollView object.

CScrollView();

Remarks

You must call either SetScrollSizes or SetScaleToFitSize before the scroll view is usable.

CScrollView::FillOutsideRect

Call FillOutsideRect to fill the area of the view that appears outside of the scrolling area.

void FillOutsideRect(
    CDC* pDC,  
    CBrush* pBrush);

Parameters

pDC
Device context in which the filling is to be done.

pBrush
Brush with which the area is to be filled.

Remarks

Use FillOutsideRect in your scroll view's OnEraseBkgnd handler function to prevent excessive background repainting.

Example

BOOL CMyScrollView::OnEraseBkgnd(CDC* pDC)
{
    CBrush br(GetSysColor(COLOR_WINDOW)); 
    FillOutsideRect(pDC, &br);
    return TRUE;                   // Erased
}

CScrollView::GetDeviceScrollPosition

Call GetDeviceScrollPosition when you need the current horizontal and vertical positions of the scroll boxes in the scroll bars.

CPoint GetDeviceScrollPosition() const;  

Return Value

The horizontal and vertical positions (in device units) of the scroll boxes as a CPoint object.

Remarks

This coordinate pair corresponds to the location in the document to which the upper-left corner of the view has been scrolled. This is useful for offsetting mouse-device positions to scroll-view device positions.

GetDeviceScrollPosition returns values in device units. If you want logical units, use GetScrollPosition instead.

CScrollView::GetDeviceScrollSizes

GetDeviceScrollSizes gets the current mapping mode, the total size, and the line and page sizes of the scrollable view.

void GetDeviceScrollSizes(
    int& nMapMode,  
    SIZE& sizeTotal,  
    SIZE& sizePage,  
    SIZE& sizeLine) const;  

Parameters

nMapMode
Returns the current mapping mode for this view. For a list of possible values, see SetScrollSizes.

sizeTotal
Returns the current total size of the scroll view in device units.

sizePage
Returns the current horizontal and vertical amounts to scroll in each direction in response to a mouse click in a scroll-bar shaft. The cx member contains the horizontal amount. The cy member contains the vertical amount.

sizeLine
Returns the current horizontal and vertical amounts to scroll in each direction in response to a mouse click in a scroll arrow. The cx member contains the horizontal amount. The cy member contains the vertical amount.

Remarks

Sizes are in device units. This member function is rarely called.

CScrollView::GetScrollPosition

Call GetScrollPosition when you need the current horizontal and vertical positions of the scroll boxes in the scroll bars.

CPoint GetScrollPosition() const;  

Return Value

The horizontal and vertical positions (in logical units) of the scroll boxes as a CPoint object.

Remarks

This coordinate pair corresponds to the location in the document to which the upper-left corner of the view has been scrolled.

GetScrollPosition returns values in logical units. If you want device units, use GetDeviceScrollPosition instead.

CScrollView::GetTotalSize

Call GetTotalSize to retrieve the current horizontal and vertical sizes of the scroll view.

CSize GetTotalSize() const;  

Return Value

The total size of the scroll view in logical units. The horizontal size is in the cx member of the CSize return value. The vertical size is in the cy member.

CScrollView::ResizeParentToFit

Call ResizeParentToFit to let the size of your view dictate the size of its frame window.

void ResizeParentToFit(BOOL bShrinkOnly = TRUE);

Parameters

bShrinkOnly
The kind of resizing to perform. The default value, TRUE, shrinks the frame window if appropriate. Scroll bars will still appear for large views or small frame windows. A value of FALSE causes the view always to resize the frame window exactly. This can be somewhat dangerous since the frame window could get too big to fit inside the multiple document interface (MDI) frame window or the screen.

Remarks

This is recommended only for views in MDI child frame windows. Use ResizeParentToFit in the OnInitialUpdate handler function of your derived CScrollView class. For an example of this member function, see CScrollView::SetScrollSizes.

ResizeParentToFit assumes that the size of the view window has been set. If the view window size has not been set when ResizeParentToFit is called, you will get an assertion. To ensure that this does not happen, make the following call before calling ResizeParentToFit:

   GetParentFrame()->RecalcLayout();

CScrollView::ScrollToPosition

Call ScrollToPosition to scroll to a given point in the view.

void ScrollToPosition(POINT pt);

Parameters

pt
The point to scroll to, in logical units. The x member must be a positive value (greater than or equal to 0, up to the total size of the view). The same is true for the y member when the mapping mode is MM_TEXT. The y member is negative in mapping modes other than MM_TEXT.

Remarks

The view will be scrolled so that this point is at the upper-left corner of the window. This member function must not be called if the view is scaled to fit.

CScrollView::SetScaleToFitSize

Call SetScaleToFitSize when you want to scale the viewport size to the current window size automatically.

void SetScaleToFitSize(SIZE sizeTotal);

Parameters

sizeTotal
The horizontal and vertical sizes to which the view is to be scaled. The scroll view's size is measured in logical units. The horizontal size is contained in the cx member. The vertical size is contained in the cy member. Both cx and cy must be greater than or equal to 0.

Remarks

With scroll bars, only a portion of the logical view may be visible at any time. But with the scale-to-fit capability, the view has no scroll bars and the logical view is stretched or shrunk to exactly fit the window's client area. When the window is resized, the view draws its data at a new scale based on the size of the window.

You'll typically place the call to SetScaleToFitSize in your override of the view's OnInitialUpdate member function. If you do not want automatic scaling, call the SetScrollSizes member function instead.

SetScaleToFitSize can be used to implement a "Zoom to Fit" operation. Use SetScrollSizes to reinitialize scrolling.

SetScaleToFitSize assumes that the size of the view window has been set. If the view window size has not been set when SetScaleToFitSize is called, you will get an assertion. To ensure that this does not happen, make the following call before calling SetScaleToFitSize:

   GetParentFrame()->RecalcLayout();

CScrollView::SetScrollSizes

Call SetScrollSizes when the view is about to be updated.

void SetScrollSizes(
    int nMapMode,  
    SIZE sizeTotal,  
    const SIZE& sizePage = sizeDefault,  
    const SIZE& sizeLine = sizeDefault);

Parameters

nMapMode
The mapping mode to set for this view. Possible values include:

All of these modes are defined by Windows. Two standard mapping modes, MM_ISOTROPIC and MM_ANISOTROPIC, are not used for CScrollView. The class library provides the SetScaleToFitSize member function for scaling the view to window size. Column three in the table above describes the coordinate orientation.

sizeTotal
The total size of the scroll view. The cx member contains the horizontal extent. The cy member contains the vertical extent. Sizes are in logical units. Both cx and cy must be greater than or equal to 0.

sizePage
The horizontal and vertical amounts to scroll in each direction in response to a mouse click in a scroll-bar shaft. The cx member contains the horizontal amount. The cy member contains the vertical amount.

sizeLine
The horizontal and vertical amounts to scroll in each direction in response to a mouse click in a scroll arrow. The cx member contains the horizontal amount. The cy member contains the vertical amount.

Remarks

Call it in your override of the OnUpdate member function to adjust scrolling characteristics when, for example, the document is initially displayed or when it changes size.

You will typically obtain size information from the view's associated document by calling a document member function, perhaps called GetMyDocSize, that you supply with your derived document class. The following code shows this approach:

   CMyScrollDoc* pMyDoc = (CMyScrollDoc*)GetDocument();
   SetScrollSizes(nMapMode, pMyDoc->GetMyDocSize());

Alternatively, you might sometimes need to set a fixed size, as in the following code:

   SetScrollSizes(nMapMode, CSize(100, 100));

You must set the mapping mode to any of the Windows mapping modes except MM_ISOTROPIC or MM_ANISOTROPIC. If you want to use an unconstrained mapping mode, call the SetScaleToFitSize member function instead of SetScrollSizes.

Example

void CMyScrollView::OnUpdate(CView* /*pSender*/, LPARAM /*lHint*/, 
   CObject* /*pHint*/)
{
   // Implement a GetMyDocSize() member function in 
   // your document class; it returns a CSize.
   CMyScrollDoc* pMyDoc = (CMyScrollDoc*)GetDocument();
   SetScrollSizes(MM_LOENGLISH, pMyDoc->GetMyDocSize());
   ResizeParentToFit();   // Default bShrinkOnly argument
}

void CMyScrollView::OnInitialUpdate()
{
   CScrollView::OnInitialUpdate();

   // The GetMyDocSize() member function is implemented in 
   // your document class. The return type is CSize.
   CMyScrollDoc* pMyDoc = (CMyScrollDoc*)GetDocument();
   SetScrollSizes(MM_TEXT, pMyDoc->GetMyDocSize());
}

See Also

MFC Sample DIBLOOK
CView Class
Hierarchy Chart
CView Class
CSplitterWnd Class