Class Public Property or Sub/Function?

[Barrabutus]

Hi guys

I was wondering if someone could explain to me the differences between these 2 ways of accessing a class property.


Access Way : 1 (To me this looks like im declaring the property of the class as a Global variable which can be changed anywhere

  Dim username As String
    Public Property user() As String
        Get
            Return username
        End Get
        Set(ByVal value As String)
            username = value.ToUpperInvariant()
        End Set
    End Property

Access Way 2: (This to me looks like the more secure way of doing the same thing.)

Dim username as String 

Public Sub setUsername(ByVal user as String)
    username = user
End Sub 

Public Function returnUserName() as String
    return username
End Function

I would just like to know when and what is the differences between the 2 methods and what is the security risks of each if possible please.

Kind Regards

Barra.

[Grimfort]

Here is what M$ suggests.

[Barrabutus]

Grimfort many thanks for the prompt reply, I have looked into the MSDN article about the differences but, I tend to struggle with all the technical terms they use lol Im quite new to classes so really all i need is someone to break that down into laymen,s terms

Like so :
Use the public property if you need to access the property directly globally
Use the Sub/Function if you need to secure it so theres only 1 way in and 1 way out of getting your property value.

I know these are probably wrong lol Its just an example

Many Thanks

Barra.

[Grimfort]

Let me extract the bit that is interesting:

•Use a method when: 
•The operation is a conversion, such as Object.ToString.     <<<< So in your example, same as doing Return Val(username)
•The operation is expensive enough that you want to communicate to the user that they should consider caching the result.  << so in your example, it could be going to a database to get the username based upon a saved userid
•Obtaining a property value using the get accessor would have an observable side effect.  <<< so reading your username, might also clear the username from your local variable
•Calling the member twice in succession produces different results.   <<< in your example, it might be the username AND the current datetime added onto the end which changes every time you call it
•The order of execution is important. Note that a type's properties should be able to be set and retrieved in any order.   <<< so setting your username and password at the same time, might cause issue if you changed them seperately and they were used by something else at the same time on a different thread (like a forms timer)

The others are less interesting
....

Heres some examples:

Private username As String

Public Property user() As String
   Get
     Return username
   End Get
    Set(ByVal value As String)
        username = value
    End Set
End Property

Public ReadOnly Property user() As String
        Get
            Return username
        End Get
End Property
  
Public ReadOnly Property user() As String
        Get
            Return username.ToUpper   '<< not a conversation, as it is still a string
        End Get
End Property

Or functions

Public Function userAsUpper() As String
   Return username.ToUpper     '<< it could be a property, there is hardly any point in arguing over it however :)
End Function

Public Sub SetUserDetails(TheUserName As String, ThePassWord As String)
   Me.username = TheUserName
   Me.password = ThePassWord
End Sub

Public Function userFormatted() As String
   Return username & " - " & Now.ToString("dd MMM yyyy hh:mm:ss")  '<< changes every time you call it
End Function

[Barrabutus]

Ah many thanks I will have to read this thread a few times for it to sink in lol

I just noticed something else that you used the ReadOnly attribute as well which i guess would help protect the property from being changed ?

Kind Regards

Barra.

[Grimfort]

Yup, you might for example use the SetUserDetails to write both username and password at the same time, but only let the user read both back through readonly properties. This will force the caller to only user your method to update. To make that scenario more complete, it could be like this:

Private UserName As String
Private Password As String

'These properties will only have values when a login is succesful
Public ReadOnly Property user() As String
        Get
            Return username
        End Get
End Property

Public ReadOnly Property pwd() As String
        Get
            Return Password
        End Get
End Property


Public Function Login(UserName As String, Password As String) As Boolean

  Try     
     'Go do a database login using the passed params
     dbOjbect.User = UserName
     dbObject.Pwd = Password
     dbObject.DoConnection()

     'Now we are connected we update the local vars so if anyone asks, we can tell them who is logged on
     Me.UserName = UserName
     Me.Password = Password
     Return True
   Catch ex As Exception
     'Failed to login for x reason
     Return False
   End Try
End Function

[Barrabutus]

Awesome explanations Grim, Many thanks it has helped clear up this question in my head

Rep added :

I do have another question lol but i,ll make a new thread

Regards Barra