问题
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
回答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
回答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.
回答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.
回答4:
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...
回答5:
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
回答6:
you should declare label first use this :
Select Case parameter
Case "userID"
' does something here.
Case "packageID"
' does something here.
Case "mvrType"
If otherFactor Then
' does something here.
Else
GoTo else
End If
Case Else
else :
' does some processing...
Exit Select
End Select
回答7:
Select Case parameter
' does something here.
' does something here.
Case "userID", "packageID", "mvrType"
If otherFactor Then
' does something here.
Else
goto case default
End If
Case Else
' does some processing...
Exit Select
End Select
回答8:
Select Case parameter
' does something here.
' does something here.
Case "userID", "packageID", "mvrType"
' does something here.
If otherFactor Then
Else
goto case default
End If
Case Else
' does some processing...
Exit Select
End Select
回答9:
Select Case parameter
Case "userID"
' does something here.
Case "packageID"
' does something here.
Case "mvrType"
If otherFactor Then
' does something here.
End If
Case Else
' does some processing...
Exit Select
End Select
Is there a reason for the goto? If it doesn't meet the if criterion, it will simply not perform the function and go to the next case.
来源：https://stackoverflow.com/questions/820104/vb-net-switch-statement-goto-case