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_VSCROLL Windows
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.
XD++
Library
Remarks