Object-Oriented Programming with Visual Basic .NET

3.2. Properties

In traditional OOP languages like C++, it is considered good practice to provide accessor methods to manipulate an object's state. For instance, if an object has a member variable named weight, a programmer often writes two functions. One function is used to get the value of weight, and another to set the value—something akin to get_Weight and set_Weight. To provide read-only access, the programmer would forego the get_ method.

Properties in VB.NET are merely a language construct used to provide this frequently used functionality and enforce good programming practice through the language.

Whenever you create a property, VB.NET automatically generates a get_ and set_ method behind the scenes. Essentially, a property is nothing more than language convenience. Check it out with ILDASM.

Properties can be ReadOnly, WriteOnly, or both. Read-only properties contain a Get block that allows retrieval of a value, but prevents it from being changed:

Public ReadOnly Property Age( ) As Double
    Get
        Return Me.age
    End Get
End Property

Write-only properties use a Set block, which allows values to be initialized but not retrieved:

Public WriteOnly Property Age( ) As Double
    Set 
        'age is a Private member variable           
        Me.age = value
    End Set
End Property

Properties that provide both read and write access must specify only an access modifier:

Public Property Age( ) As Double Get Return ...