SAMPLE: Using Enumerated Properties in an OLE Control

ID: Q141488

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1

This is the 32-bit version of this sample.

SUMMARY

The ENPROP32 sample illustrates using enumerated properties in an OLE control.

The following file is available for download from the Microsoft Software Library:

~ Enprop32.exe

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:

Q119591 How to Obtain Microsoft Support Files from Online Services

MORE INFORMATION

The ENPROP32 sample illustrates using enumerated properties in an OLE control. An enumerated property is one which has a specific set of possible values. For example, an OLE control might support a property named FillPattern which it uses to determine the type of brush to use when drawing the control. The control would want to limit the values the FillPattern property could be set to. Accepted values for a FillPattern property might be cross-hatched, vertical lines, horizontal lines, etc.

An OLE control can limit the values a user has to choose from for a property by using a Drop List combo box on its property page. However, another mechanism is needed to enable a property browser provided by another application to be able to provide the same type of interface when editing the property.

There are two ways to implement an enumerated property so that a property browser can gather enough information about the property to provide the right editing interface. One method involves declaring an enum type in the OLE control's .odl file and manually editing the property's declaration to make it be of that type. For example:


  ...

  typedef enum
  {
    [helpstring("Solid")]        Solid      = 0,
    [helpstring("Dash")]         Dash       = 1,
    [helpstring("Dot")]          Dot        = 2,
    [helpstring("Dash-Dot")]     DashDot    = 3,
    [helpstring("Dash-Dot-Dot")] DashDotDot = 4,
  } enumLineStyle;

  ...

  properties:

  // NOTE - ClassWizard will maintain property information here.
  //    Use extreme caution when editing this section.
  //{{AFX_ODL_PROP(CEnumCtrl)
    [id(1)] enumLineStyle LineStyle;
  //}}AFX_ODL_PROP

Another method involves overriding the COleControl methods OnGetPredefinedStrings, OnGetPredefinedValue, and OnGetDisplayString. The ENUMPROP sample illustrates using both methods. The OLE control implemented in the sample supports two custom properties, LineStyle and FillPattern. The LineStyle property is declared as an enum in the control's .odl file. Support for using the FillPattern property as an enumerated property is handled via overrides of the OnGetPredefinedStrings, OnGetPredefinedValue, and OnGetDisplayString methods.

ENPROP32 is based on a ControlWizard generated OLE control. Files included with the sample, which are directly related to using enumerated properties, are:

ENUM.ODL -
Shows declaring the enum type for the LineStyle property.

ENUMCTL.CPP -
Illustrates overriding the COleControl members OnGetPredefinedStrings, OnGetPredefinedValue, and OnGetDisplayString.

RFERENCES

The Per-Property Browsing section in Appendix D, OLE Controls Architecture, in the CDK Books Online.

NOTE: The OLE Control Test Container provided with Visual C++ does not implement a Drop List combobox on its property browser page when editing an enumerated property. To see the full benefits of using an enumerated property, use an OLE control container application which provides a property browser with this capability, such as Visual Basic 4.0.

Additional query words: Enumprop

Keywords : kbcode kbole kbsample kbMFC kbVC
Version : 4.00 4.10
Platform : NT WINDOWS
Issue type :