Hidden Features of VB.NET?

The Exception When clause is largely unknown.

Consider this:

Public Sub Login(host as string, user as String, password as string, _
                            Optional bRetry as Boolean = False)
Try
   ssh.Connect(host, user, password)
Catch ex as TimeoutException When Not bRetry
   ''//Try again, but only once.
   Login(host, user, password, True)
Catch ex as TimeoutException
   ''//Log exception
End Try
End Sub

Oh! and don't forget XML Literals.

Dim contact2 = _
        <contact>
          <name>Patrick Hines</name>
          <%= From p In phoneNumbers2 _
            Select <phone type=<%= p.Type %>><%= p.Number %></phone> _
          %>
        </contact>

This is a nice one. The Select Case statement within VB.Net is very powerful.

Sure there is the standard

Select Case Role
  Case "Admin"
         ''//Do X
  Case "Tester"
         ''//Do Y
  Case "Developer"
         ''//Do Z
  Case Else
       ''//Exception case
End Select

But there is more...

You can do ranges:

Select Case Amount
 Case Is < 0
    ''//What!!
 Case 0 To 15
   Shipping = 2.0
 Case 16 To 59
    Shipping = 5.87
 Case Is > 59
    Shipping = 12.50
 Case Else
    Shipping = 9.99
 End Select

And even more...

You can (although may not be a good idea) do boolean checks on multiple variables:

Select Case True
 Case a = b
    ''//Do X
 Case a = c
    ''//Do Y
 Case b = c
    ''//Do Z
 Case Else
   ''//Exception case
 End Select

• AndAlso/OrElse logical operators

(EDIT: Learn more here: Should I always use the AndAlso and OrElse operators?)

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

Unlike break in C languages in VB you can Exit or Continue the block you want to:

For i As Integer = 0 To 100
    While True
        Exit While
        Select Case i
            Case 1
                Exit Select
            Case 2
                Exit For
            Case 3
                Exit While
            Case Else
                Exit Sub
        End Select
        Continue For
    End While
Next

VB also offers the OnError statement. But it's not much of use these days.

On Error Resume Next
' Or'
On Error GoTo someline

Private Sub Button1_Click(ByVal sender As Button, ByVal e As System.EventArgs)
        Handles Button1.Click
    sender.Enabled = True
    DisableButton(sender)
End Sub

Private Sub Disable(button As Object)
    button.Enabled = false
End Sub

In this snippet you have 2 (maybe more?) things that you could never do in C#:

1. Handles Button1.Click - attach a handler to the event externally!
2. VB's implicitness allows you to declare the first param of the handler as the expexted type. in C# you cannot address a delegate to a different pattern, even it's the expected type.

Also, in C# you cannot use expected functionality on object - in C# you can dream about it (now they made the dynamic keyword, but it's far away from VB). In C#, if you will write (new object()).Enabled you will get an error that type object doesn't have a method 'Enabled'. Now, I am not the one who will recommend you if this is safe or not, the info is provided AS IS, do on your own, bus still, sometimes (like when working with COM objects) this is such a good thing. I personally always write (sender As Button) when the expected value is surely a button.

Actually moreover: take this example:

Private Sub control_Click(ByVal sender As Control, ByVal e As System.EventArgs)
        Handles TextBox1.Click, CheckBox1.Click, Button1.Click
    sender.Text = "Got it?..."
End Sub