Friend (Visual Basic)

Статья
02/04/2013

Specifies that one or more declared programming elements are accessible only from within the assembly that contains their declaration.

Remarks

The following class uses the Friend modifier to allow other programming elements within the same assembly to access certain members.

Class CustomerInfo

    Private p_CustomerID As Integer

    Public ReadOnly Property CustomerID() As Integer
        Get
            Return p_CustomerID
        End Get
    End Property

    ' Allow friend access to the empty constructor.
    Friend Sub New()

    End Sub

    ' Require that a customer identifier be specified for the public constructor.
    Public Sub New(ByVal customerID As Integer)
        p_CustomerID = customerID
    End Sub

    ' Allow friend programming elements to set the customer identifier.
    Friend Sub SetCustomerID(ByVal customerID As Integer)
        p_CustomerID = customerID
    End Sub
End Class

Rules

Declaration Context. You can use Friend only at module, interface, or namespace level. This means the declaration context for a Friend element must be a source file, namespace, interface, module, class, or structure, and cannot be a procedure.
Combined Modifiers. You can use the Friend modifier in conjunction with the Protected (Visual Basic) modifier in the same declaration. This combination confers both friend and protected access on the declared elements, so they are accessible from anywhere in the same assembly, from their own class, and from derived classes. You can specify Protected Friend only on members of classes.

Behavior

Access Level. All code within a declaration context can access its elements. Code in other classes, structures, and modules that are compiled to the same assembly can access all the Friend elements in that assembly.

Friend access is not a superset or subset of protected access.
Access Modifiers. The keywords that specify access level are called access modifiers. For a comparison of the access modifiers, see Access Levels in Visual Basic.

When to Use Friend

In many cases, you want programming elements such as classes and structures to be used by the entire assembly, not only by the component that declares them. However, you might not want them to be accessible by code outside the assembly, for example if the application is proprietary. If you want to limit access to an element in this way, you can declare it with Friend.

Friend access is often the preferred level for an application's programming elements. Note that the access level of an interface, module, class, or structure defaults to Friend if you do not declare it otherwise.

The Friend modifier can be used in these contexts: