Declaring Obsolete Methods in your C# and VB.NET Classes

When building class libraries, it is important to let developers know when a piece of functionality is considered obsolete. In .Net this is possible by decorating a method or a property with the Obsolete attribute. By using this attribute you can display a message to the developer when they use this informing them this is an obsolete function, or even throw an error preventing them from using the function.

In the below example, a method is decorated with the attribute but the user can still compile the application:

C#

public class OldMethods
{
    [Obsolete("This method will be removed from future versions")]
    public void MyOldMethod()
    {
    }

    public void MyNewMethod()
    {

    }
} 

VB.NET

Public Class OldMethods
    <Obsolete("This method will be removed from future versions")> _
    Public Sub MyOldMethod()
    End Sub

    Public Sub MyNewMethod()

    End Sub
End Class

The developer will see a nicely formatted message when using this function:

You can also prevent code from being compiled if the developer uses the old method by adding a boolean value after the message:

C#

public class OldMethods
{
    [Obsolete("This method will be removed from future versions", true)]
    public void MyOldMethod()
    {
    }

    public void MyNewMethod()
    {
    }
}

VB.NET

Public Class OldMethods
    <Obsolete("This method will be removed from future versions", True)> _
    Public Sub MyOldMethod()
    End Sub

    Public Sub MyNewMethod()
    End Sub
End Class

Now when the developer tries to compile their code they will see a compilation error: