Understand a Friend

[Liquid Metal]

I just converted one of my VB6 project using the 2005 Wizard.

I understand the concept of Public and Private but what is Friend? Also, is there anything else in the same line as this?

Thank You

[jmcilhinney]

Access Levels in Visual Basic

Friend behaves like Public within the project it was declared in and like Private outside that project.

[Liquid Metal]

Thank You for the quick explanation.

I am having trouble going to the url that you provided.

Also, there is Protected and Protected Friend.

[jmcilhinney]

MSDN seems to be labouring at the moment. It loaded really slowly for me too. Maybe they're having server issues at the moment. Give it time. Protected Friend is like Public within the project it was declared in (that's the Friend part) and like Protected outside that project. It is the least commonly used access level.

[Liquid Metal]

Thank You but I actually found this too.

http://msdn.microsoft.com/library/de...vastmclass.asp

However, still a bit confuse on Protected.

Also, I should be using Friend if I know that another program is not going to access this program right?

Thank You

[jmcilhinney]

You should pretty much declare all your types as Friend in an application. If you declare the type itself as Friend then you can leave all the members as Public and they are still inaccessible outside the assembly. With library projects its a bit both ways. If you intend for the applications that reference your library to use a type then declare it as Public, but if it is only supposed to be used within your library by your own types then declare it as Friend. The C# equivalent of Friend is "internal", which probably is a bit more descriptive.

Here's an example of the difference between Public, Protected and Private:

Public Class Class1
    Public var1 As Integer
    Protected var2 As Integer
    Private var3 As Integer
End Class
 
Public Class Class2
    Inherits Class1
 
    Public Sub Sub1()
        Me.var1 = 1 '<- OK.  Public member variable inherited from Class1
        Me.var2 = 2 '<- OK.  Protected member variable inherited from Class1
        Me.var3 = 3 '<- Not allowed.  Private member not inherited from Class1
    End Sub
 
    Public Sub Sub2()
        Dim c1 As New Class1
 
        c1.var1 = 1 '<- OK.  Public member accessible from outside Class1
        c1.var2 = 2 '<- Not allowed.  Protected member not accessible from outside Class1
        c1.var3 = 3 '<- Not allowed.  Private member not accessible from outside Class1
    End Sub
End Class

[Liquid Metal]

Thanks for taking out the time to create the example.

OK, so this is what I tried to make sense out from your example and if I am wrong, forgive me.

Public - Anything can access it.
Private - Only on a Module Level can access it.
Protected - It is in a way like Private but can only be access from inheritance.

If the above is correct, when would I use Protected?

[jmcilhinney]

One of the most common uses of Protected is on the methods that raise events within a class. For instance, the TextChanged event of the Control class is raised by the OnTextChanged method, which is declared Protected. You don't want just anybody to be able to raise your TextChanged event, so you don't want the OnTextChanged method accessible from outside the class. If you create your own control though, you'll need to be able to raise its TextChanged event, so you do want the OnTextChanged method accessible from within classes that inherit Control. That's exactly how Protected works.