Hidden Features of VB.NET?

Question

I have learned quite a bit browsing through Hidden Features of C# and was surprised when I couldn't find something similar for VB.NET.

So what are some of its hidden or lesser known features?

Answer 1

Consider the following event declaration

Public Event SomethingHappened As EventHandler

In C#, you can check for event subscribers by using the following syntax:

if(SomethingHappened != null)
{
  ...
}

However, the VB.NET compiler does not support this. It actually creates a hidden private member field which is not visible in IntelliSense:

If Not SomethingHappenedEvent Is Nothing OrElse SomethingHappenedEvent.GetInvocationList.Length = 0 Then
...
End If

More Information:

http://jelle.druyts.net/2003/05/09/BehindTheScenesOfEventsInVBNET.aspx http://blogs.msdn.com/vbteam/archive/2009/09/25/testing-events-for-nothing-null-doug-rothaus.aspx

Answer 2

There are a couple of answers about XML Literals, but not about this specific case:

You can use XML Literals to enclose string literals that would otherwise need to be escaped. String literals that contain double-quotes, for instance.

Instead of this:

Dim myString = _
    "This string contains ""quotes"" and they're ugly."

You can do this:

Dim myString = _
    <string>This string contains "quotes" and they're nice.</string>.Value

This is especially useful if you're testing a literal for CSV parsing:

Dim csvTestYuck = _
    """Smith"", ""Bob"", ""123 Anywhere St"", ""Los Angeles"", ""CA"""

Dim csvTestMuchBetter = _
    <string>"Smith", "Bob", "123 Anywhere St", "Los Angeles", "CA"</string>.Value

(You don't have to use the <string> tag, of course; you can use any tag you like.)

Answer 3

If you need a variable name to match that of a keyword, enclose it with brackets. Not nec. the best practice though - but it can be used wisely.

e.g.

Class CodeException
Public [Error] as String
''...
End Class

''later
Dim e as new CodeException
e.Error = "Invalid Syntax"

e.g. Example from comments(@Pondidum):

Class Timer
Public Sub Start()
''...
End Sub

Public Sub [Stop]()
''...
End Sub

Answer 4

Optional Parameters

Optionals are so much easier than creating a new overloads, such as :

Function CloseTheSystem(Optional ByVal msg AS String = "Shutting down the system...")
   Console.Writeline(msg)
   ''//do stuff
End Function

Answer 5

In vb there is a different between these operators:

/ is Double
\ is Integer ignoring the remainder

Sub Main()
    Dim x = 9 / 5  
    Dim y = 9 \ 5  
    Console.WriteLine("item x of '{0}' equals to {1}", x.GetType.FullName, x)
    Console.WriteLine("item y of '{0}' equals to {1}", y.GetType.FullName, y)

    'Results:
    'item x of 'System.Double' equals to 1.8
    'item y of 'System.Int32' equals to 1
End Sub

Answer 6

The Using statement is new as of VB 8, C# had it from the start. It calls dispose automagically for you.

E.g.

Using lockThis as New MyLocker(objToLock)

End Using