Select Case on an object's type in VB.NET
Solution 1
With VB 2010, for projects targeting .NET framework 4 and later, you can now do this:
Select Case msg.GetType()
Case GetType(ClassA)
End Select
In earlier VB versions, it didn't work because you couldn't compare two types with equality. You'd have to check if they point to the same reference using the Is keyword. It's not possible to do this in a Select Case, unless you use a property of the type like the Name or FullName for comparison, as suggested by Michael. You can use a combination of If and ElseIf though:
Dim type = msg.GetType()
If type Is GetType(ClassA)
...
ElseIf type Is GetType(ClassB)
...
...
End If
Solution 2
Well, if you insist on using Select Case, you could always go with:
Select Case True
Case TypeOf msg Is ClassA
' do something '
Case TypeOf msg Is ClassB
' do something else '
Case Else
' and so on '
End Select
But I would imagine most people like to avoid this kind of thing. If/ElseIf would probably be clearer.
Solution 3
This is a way to handle Button1 and Button2 click events in the same sub (I started out as a VB6 programmer, so this is a good substitute for VB6 handling of control arrays)
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click, Button2.Click
Select Case True
Case sender Is Me.Button1
' Do Button1 stuff '
Case sender Is Me.Button2
' Do Button2 stuff '
End Select
End Sub
Solution 4
I wouldn't ever select case true
, but you can do this:
Select Case msg.GetType.Name
Case GetType(ClassA).Name
...
Case GetType(ClassB).Name
...
Case Else
...
End Select
Which is slighly cleaner looking than this:
If msg.GetType Is GetType(ClassA) Then
...
ElseIf msg.GetType Is GetType(ClassB) Then
...
Else
...
End If
Solution 5
This:
Dim a As Object = New TextBox
Select Case True
Case TypeOf a Is TextBox
MsgBox("aaa")
Case TypeOf a Is ComboBox
Case TypeOf a Is ListBox
End Select
Comments
-
mcjabberz almost 2 years
I'm not sure if this valid C#, but hopefully you get the idea. :)
switch (msg.GetType()) { case ClassA: // blah case ClassB: // blah 2 case ClassC: // blah 3 }
How would I switch on an object's type but using VB.NET's
Select Case
?I'm aware that some might suggest using polymorphism, but I'm using a hierarchy of small message classes so that really wouldn't work in my case.
-
MarkJ over 14 yearsPlease do avoid this sort of thing! :)
-
mcjabberz over 14 yearsI'm just going to use
If
/ElseIf
s. Kinda sucks that there's not a switch-like way to do it. -
Bernesto over 12 yearsIt may be more sightly, but is also about a hundred times slower too. But it would get the job done if he really wants to do it that way.
-
Mr Shoubs over 12 years@Bernesto - A hundred times slower than what? This answer is the same as the accepted answer (I don't have 2010 to test the performance of type equality). I don't believe it should be a -1??
-
Aravinth almost 12 yearsTo be specific, this will only work in .Net Framework 4 and later. Type.Equality Operator
-
Airn5475 over 11 yearsYou can take this with a grain of salt and do your own perf testing: My own simple performance test of
If/ElseIf
vsSelect Case
proved theIf/ElseIf
option was faster every time. TheSelect Case
took roughly 4 times as long. I'll stick withIf/ElseIf
for now. -
lb. over 10 yearsIf Type.Name is not a fully qualified type name there may be a conflict if two classes have the same name but are in different namespaces.
-
lb. over 10 yearsI am ambivalent on this one if the block is short. What would be the argument against this section of code?
-
Germán Martínez over 10 yearsActually this does not seem bad at all, especially when you might have multiple cases (fall-through) - this would look MILES better than if statements...
-
rheitzman over 8 yearsI prefer CASE over nested IFs - much more readable and less error prone IMO. I use SELECT CASE True ... often, works great.
-
user3085342 over 6 yearsThanks - this allows for more succinct / easier-to-read code when checking for 2 different types in same comparison eg
Case GetType(ClassA), GetType(ClassB)
vsElseif typeof obj is ClassA or typeof obj is ClassB then
-
Tom Lint about 6 years@MrShoubs "A hundred times slower than what?" You do realize that, unlike the accepted answer, which just compares Type instances, your answer creates strings for each of them and compares those, instead?