Property Procedures

[tiredofit]

I have read an article which states the following:

" ..... when you use Property procedures, your class is aware of changes made to a property

value. If you use public variables, you have no way of knowing when a consumer procedure changes​

a given property’s value."

Can some one please explain / give an example of the statement:

"If you use public variables, you have no way of knowing when a consumer procedure changes
a given property’s value."


Thanks

 

[RoryA]

Let's say you have a class called Class1 and you need to expose a Boolean value from it. You can do this in two ways - either using a property procedure, or using a public variable. If you use a public variable, like:

Public Changed as Boolean

the calling code can change the value using code like this:

Dim myClass as Class1
Set myClass = New Class1
myClass.Changed = True

which will change the value of the variable directly, and your class code has no way of reacting to this change, other than say by periodically checking the value of the variable.

If, on the other hand you use a property procedure:

' code in Class1
Private m_bChanged As Boolean
Public Property Get Changed() As Boolean
   Changed = m_bChanged
End Property
Public Property Let Changed(ByVal bChanged As Boolean)
   m_bChanged = bChanged
   msgbox "The variable has been changed!"
End Property

the only way the calling routine (code for that is the same either way) can change the value of the mb_Changed variable is by calling the property procedure which can automatically run whatever code you require (in this example, the msgbox code).

Does that help?

 

[tiredofit]

Yes, thanks.