Programming Excel with VBA and .NET

Define Enumerations

Enumerations are a handy way to publish the possible settings for a property. For example, the following addition to the Message class allows users to set the icon that appears on the message when it is shown:

    Public Icon As IconType

    Enum IconType
        None
        Critical = VbMsgBoxStyle.vbCritical
        Warning = VbMsgBoxStyle.vbExclamation
        Question = VbMsgBoxStyle.vbQuestion
        Information = VbMsgBoxStyle.vbInformation
    End Enum

    ' Show method: displays the message.
    Public Sub Show( )
        MsgBox value, Me.Icon, Title
    End Sub

I added Me.Icon to the Show method to display the appropriate icon in the MsgBox. The point of using an enumeration is that the available settings are now automatically listed when you set the property, as shown in Figure 5-4.

You can use enumerations within methods as well. For example, the following changes allow the Show method to accept an icon setting:

    Public Sub Show(Optional icon As IconType = -1)
        If (icon = -1) Then icon = Me.icon
        MsgBox value, icon, Title
    End Sub

In the preceding code, I made icon an optional argument with a default setting outside of the possible IconType values so I can tell whether or not the argument was set. If icon is omitted, I use the setting from the Icon property instead. In this case, the icon argument overrides the Icon property.

When you use Show, Visual Basic displays the possible settings for the icon argument, as shown in Figure 5-5.

Figure 5-4. Use enumerations to publish available settings

Figure 5-5. Enumerations are handy ...