VB.NET Switch Statement GoTo Case

Question

I am writing some code in VB.NET that uses a switch statement but in one of the cases it needs to jump to another block. In C# it would look like this:

switch (parameter)
{
    case "userID":
        // does something here.
    case "packageID":
        // does something here.
    case "mvrType":
        if (otherFactor)
        {
            // does something here.
        }
        else
        {
            goto default;
        }
    default:
        // does some processing...
        break;
}

However, I don't know how to convert this to VB.NET. I tried this:

Select Case parameter 
    Case "userID"
        ' does something here.
    Case "packageID"
        ' does something here.
    Case "mvrType" 
        If otherFactor Then 
            ' does something here. 
        Else 
            GoTo Case Else 
        End If 
    Case Else 
        ' does some processing... 
        Exit Select 
End Select     

But when I do this I get a compiler error: "Identifier expected". There'sa squiggly line under "Case". Any ideas?

Also, is it wrong to use a GoTo statement in this case? It seems any other way I would have to re-write it.

---

I have changed my code to as follows:

If otherFactor AndAlso parameter = "mvrType" Then 
    'does something here 
Else 
    ' My original "Select Case statement" here without the case for "mvrType" 
End If

Solution 1

There is no equivalent in VB.NET that I could find. For this piece of code you are probably going to want to open it in Reflector and change the output type to VB to get the exact copy of the code that you need. For instance when I put the following in to Reflector:

switch (args[0])
{
    case "UserID":
        Console.Write("UserID");
        break;
    case "PackageID":
        Console.Write("PackageID");
        break;
    case "MVRType":
        if (args[1] == "None")
            Console.Write("None");
        else
            goto default;
        break;
    default:
        Console.Write("Default");
        break;
}

it gave me the following VB.NET output.

Dim CS$4$0000 As String = args(0)
If (Not CS$4$0000 Is Nothing) Then
    If (CS$4$0000 = "UserID") Then
        Console.Write("UserID")
        Return
    End If
    If (CS$4$0000 = "PackageID") Then
        Console.Write("PackageID")
        Return
    End If
    If ((CS$4$0000 = "MVRType") AndAlso (args(1) = "None")) Then
        Console.Write("None")
        Return
    End If
End If
Console.Write("Default")

As you can see you can accomplish the same switch case statement with If statements. Usually I don't recommend this because it makes it harder to understand, but VB.NET doesn't seem to support the same functionality, and using Reflector might be the best way to get the code you need to get it working with out a lot of pain.

Update:

Just confirmed you cannot do the exact same thing in VB.NET, but it does support some other useful things. Looks like the IF statement conversion is your best bet, or maybe some refactoring. Here is the definition for Select...Case

http://msdn.microsoft.com/en-us/library/cy37t14y.aspx

Solution 2

Why not just do it like this:

Select Case parameter     
   Case "userID"                
      ' does something here.        
   Case "packageID"                
      ' does something here.        
   Case "mvrType"                 
      If otherFactor Then                         
         ' does something here.                 
      Else                         
         ' do processing originally part of GoTo here
         Exit Select  
      End If      
End Select

I'm not sure if not having a case else at the end is a big deal or not, but it seems like you don't really need the go to if you just put it in the else statement of your if.

Solution 3

Why don't you just refactor the default case as a method and call it from both places? This should be more readable and will allow you to change the code later in a more efficient manner.

Solution 4

In VB.NET, you can apply multiple conditions even if the other conditions don't apply to the Select parameter. See below:

Select Case parameter 
    Case "userID"
                ' does something here.
        Case "packageID"
                ' does something here.
        Case "mvrType" And otherFactor
                ' does something here. 
        Case Else 
                ' does some processing... 
End Select

Solution 5

I'm not sure it's a good idea to use a GoTo but if you do want to use it, you can do something like this:

Select Case parameter 
    Case "userID"
        ' does something here.
    Case "packageID"
        ' does something here.
    Case "mvrType" 
        If otherFactor Then 
            ' does something here. 
        Else 
            GoTo caseElse
        End If 
    Case Else
caseElse:
        ' does some processing... 
End Select

As I said, although it works, GoTo is not good practice, so here are some alternative solutions:

Using elseif...

If parameter = "userID" Then
    ' does something here.
ElseIf parameter = "packageID" Then
    ' does something here.
ElseIf parameter = "mvrType" AndAlso otherFactor Then
    ' does something here.
Else
    'does some processing...
End If

Using a boolean value...

Dim doSomething As Boolean

Select Case parameter
Case "userID"
     ' does something here.
Case "packageID"
     ' does something here.
Case "mvrType"
     If otherFactor Then
          ' does something here. 
     Else
          doSomething = True
     End If
Case Else
     doSomething = True
End Select

If doSomething Then
     ' does some processing... 
End If

Instead of setting a boolean variable you could also call a method directly in both cases...

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