How to implement enumerated properties in ATL

MORE INFORMATION

The following files are available for download from the Microsoft Download Center:

Visual C++ 6.0

For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

Visual C++ .NET

Release Date: June 25, 2002

For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

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 and later versions have 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 - Monday," "2 - 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.