SAMPLE: How To Implement Enumerated Properties in ATL

ID: Q181255

The information in this article applies to:

SUMMARY

The Atlenum sample shows how to implement enumerated properties in ATL.


MORE INFORMATION

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

~ atlenum.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
Enumerated properties have a predefined set of possible values that you can assign to them. For example, when you define an enumerated property for the days of the week, the only possible values are Monday through Sunday. You can control this by setting up an enumerated property in the .idl file: 

   typedef enum tagDAYSOFWEEK
   {
      Monday   = 1,
      Tuesday   = 2,
      Wednesday   = 3,
      Thursday   = 4,
      Friday   = 5,
      Saturday   = 6,
      Sunday   = 7
   } DAYSOFWEEK;
Visual Basic 5.0 has a feature called Code Completion. As you enter code, the editor displays a list of context-sensitive items that you can use in your code. In the case of an enumerated property, typing an "=" after the property causes Visual Basic to display a list of possible values. For example, a list of possible values to complete the following statement appears when you type: 

   mycontrol.DayOfWeek =
Enumerated properties also allow you to browse the possible values for a property in a property browser. Look at the BorderStyle property for any control in the Visual Basic property browser. Possible values are displayed in a list box. By default, Visual Basic creates a list in the form of "1 [ASCII 150] Monday," "2 [ASCII 150] Tuesday," and so on. If you want to the change the display string, you need to override some methods in the IPerPropertyBrowsing interface. The Atlenum sample shows how to override the GetDisplayString(), GetPredefinedStrings(), and GetPredefinedValue() methods. The sample also implements a property page for modifying the enumerated property.

For additional information on how to implement enumerated properties in the Microsoft Foundation Classes (MFC), please see the following article in the Microsoft Knowledge Base:
Q141488 SAMPLE: Using Enumerated Properties in an OLE Control
If you are converting MFC projects to ATL, you can leave out the tag after the enum keyword in an .odl file, as in the following example: 


   typedef enum
   {
... 

   } DAYSOFWEEK;


In an .idl file, you need to have a tag after the enum keyword to ensure that you have the right type information: 

   typedef enum tagDAYSOFWEEK
   {
      ...
   } DAYSOFWEEK; 


Keywords          : kbcode kbfile kbsample kbActiveX kbATL210 kbCtrl kbServer kbVC500 kbVC600 kbATL300 kbCodeSam 
Version           : WINDOWS:2.1,3.0
Platform          : WINDOWS 
Issue type        : kbhowto

Last Reviewed: July 21, 1999