Graphics Device Interface (GDI) functionality is
encapsulated by the CDC class (representing device
contexts), the CGdiObject class (representing GDI
objects), and classes derived from both.
classes include CClientDC (representing a window's
interior), CWindowDC (representing a window), and CPaintDC
(representing a device context while processing a WM_PAINT
message). These derived classes only differ from the base
class inasmuch as their constructor and destructor
encapsulate calls that create and destroy the appropriate
GDI device context (for example, by calling GetDC and
ReleaseDC, or BeginPaint/EndPaint). In contrast, a base
CDC object is not automatically attached to a GDI device
context; the device context must be explicitly created
through the CreateDC member function (or attached to
through the Attach member function).
class derived from CDC is CMetafileDC, which represents
metafile device contexts.
A CDC object
maintains two GDI device context handles. The output
device context handle is used for drawing operations; the
attribute device context handle is used for operations
obtaining information about the device context. The two
handles are usually identical, except for the case of
CMetafileDC objects, in which case the attribute device
context is set to NULL.
class encapsulates most GDI drawing functionality. This
includes basic drawing functions, simple lines and shapes,
text and font functions, clipping functions, bitmap and
scrolling functions, and region and path-related
functions. The CDC class also provides functionality
related to mapping modes. Note that encapsulation of the
Windows NT world coordinate transformation functions is
not provided as part of the CDC class.
operations utilize drawing tools that are selected into a
device context using the SelectObject or SelectStockObject
functions. These tools are GDI objects such as pens,
brushes, palettes, bitmaps, fonts, and regions. Support
for these GDI objects in MFC is provided through a series
of classes derived from CGdiObject. The CPen, CBrush,
CFont, CBitmap, CPalette, and CRgn classes encapsulate the
functionality of pens, brushes, fonts, bitmaps, palettes,
and regions, respectively.
utilize this variable, I added a message handler function
for the Describe button. In this function, shown in
Listing 23.3, I retrieve the control's Shape property by
calling the COCTL::GetShape member function and display
the result in a message box.
// TODO: Add your control notification handler code here
case 0: shape = "Ellipse"; break;
case 1: shape = "Rectangle"; break;
case 2: shape = "Triangle"; break;
AfxMessageBox("The control's shape is " + shape + ".");
messages from an OLE custom control is perhaps even
simpler than handling properties. You can add handlers for
any event the control supports via ClassWizard. For
example, Figure 23.9 demonstrates adding a message handler
for the single event that the OCTL control can generate, a
Figure 9. Adding a message map entry for an OLE custom
the type of the event, the event handler may receive
parameters. In the case of OCTL, a handler for the Select
event received a Boolean parameter specifying whether the
control has just been selected or deselected. The sample
handler function in ODLG simply displays a message box to
this effect, as shown in Listing 23.4.
void CODLGDlg::OnSelectOctlctrl(BOOL IsSelected)
// TODO: Add your control notification handler code here
AfxMessageBox("The control has been selected.");
AfxMessageBox("The control has been deselected.");
there is to it! All that remains is recompiling and
running your application.
As you can
see, the procedure for inserting an OLE custom control is
no more complex than the procedure for inserting other
types of controls. Moreover, in order to efficiently use
an OLE custom control, you need not know the details of
its implementation (or even how OLE custom controls are
implemented in the first place). All you need is
documentation on the control's purpose and behavior, its
properties, methods, and events.
Microsoft really delivered on its promise of providing a
32-bit custom control technology that is superior to VBX
technology. All we need now is a variety of wonderful
third-party custom controls.
supplies several OLE custom controls with Visual C++.
These controls are similar in function and appearance to
VBX controls found in earlier versions (for example,
Version 3.0) of Visual Basic.
controls is the Animated Button Control; this flexible
control can be used to implement multistate or animated
Control presents a two-dimensional array of cells
organized into rows and columns in a spreadsheet-like
State Control can be used to display the state of the Num
Lock, Caps Lock, or Scroll Lock keys or the
Microsoft Comm control is an example of a control that is
not visible at runtime. This control provides a
communication port interface.
Microsoft Masked Edit Control provides an edit control
with customized, formatted editing capabilities.
Microsoft Multimedia Control provides a programmatic
control is yet another control that is not visible at
runtime; this control provides an efficient mechanism for
organizing a large number of small icons or bitmaps.
these controls (the Animated Button Control, the Grid
Control, the Key State Control, and the Microsoft
Multimedia Control) are demonstrated in a dialog box shown
in Figure 23.10.
Figure 10. Some custom controls supplied with Visual
controls represent a technology that is a 32-bit successor
to the Visual Basic custom control (VBX) technology.
In order for
an application to act as an OLE control container, it is
necessary to call the AfxEnableControlContainer function
when the application is being initialized.
controls can be used in applications just like ordinary
controls. They can be inserted into a dialog template
using the Developer Studio dialog editor. The control can
be configured through a set of property page interfaces
that appear in the control's property sheet in the dialog
control's properties can be accessed from within the
application by using the ClassWizard to add member
variables that correspond to the control. When adding a
member variable for a certain type of control for the
first time, ClassWizard creates a wrapper class for the
control and adds it to the project.
ClassWizard can also be used to add handler functions for
supplies several custom controls as part of the Visual
mfc example C++
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