I need a little help here.

  • Thread starter Thread starter Carlos Yakimov
  • Start date Start date
C

Carlos Yakimov

I want to convert this C# Linq Query into VB.NET

void Load() {
int i = 1;
var q = from P in Persons
select new System.Windows.Forms.ListViewItem( P.Name, i++ );
}

I did this:

Sub Load()
Dim I As Integer = 1
Dim q = from P in Persons _
Select New ListViewItem(P.Name, i++
? )
End Sub

My problem is how I can use the ++ Operator in Vb?

Thanks in advance.
 
Carlos, the ++ operator in C# uses the current value, if it's involved in an
expression of any kind, and then increments it after use. So in the C# code,
it will use the i value of 1 as an argument in the select, and then will set
it to 2 afterwards.

So the equivalent in VB.Net would be:

Sub Load()

Dim i As Integer = 1

Dim q = from P in Persons _
Select New ListViewItem(P.Name, i)
i += 1

' Other code follows, presumably...

End Sub


Tom Dacon
Dacon Software Consulting
 
Tom Dacon said:
Carlos, the ++ operator in C# uses the current value, if it's involved in
an expression of any kind, and then increments it after use. So in the C#
code, it will use the i value of 1 as an argument in the select, and then
will set it to 2 afterwards.

So the equivalent in VB.Net would be:

Sub Load()

Dim i As Integer = 1

Dim q = from P in Persons _
Select New ListViewItem(P.Name, i)
i += 1

' Other code follows, presumably...

End Sub


Tom Dacon
Dacon Software Consulting
Click to expand...

I tried this and the C# version would provide an incremented value for each
listviewitem created. So you would expect a collection of listviewitems
where the imageIndex would start at 1 and increment for each item.

When you try the code in VB (and I have no idea why) you end up with a list
of listviewitems and each has an imageIndex of 2. If I change the code to i
+=2 then the items have an imageIndex of 3. It seems that the final
increment is what is used as if the value is not created until used.

LS
 
Lloyd Sheen said:
I tried this and the C# version would provide an incremented value for
each listviewitem created. So you would expect a collection of
listviewitems where the imageIndex would start at 1 and increment for each
item.

When you try the code in VB (and I have no idea why) you end up with a
list of listviewitems and each has an imageIndex of 2. If I change the
code to i +=2 then the items have an imageIndex of 3. It seems that the
final increment is what is used as if the value is not created until used.

LS
Click to expand...

Ok I think you can use a function to do the incrementing:

Dim Persons() As String = {"Him", "Her", "Them"}


Dim ii As Integer = 0

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim tst = From t In Persons _
Select New ListViewItem(t, GiveMeAnInt(t))

Dim i As Integer = tst.Count
Dim tl As List(Of ListViewItem) = tst.ToList
End Sub

Private Function GiveMeAnInt(ByVal tmp As String) As Integer
ii += 1
Return ii
End Function


Once again though the imageIndex values are in fact 4,5,6 which I think
confirms that somehow the values are being put in at a time other than what
I would think is correct. Linq has its values but I don't think that in
the case of VB that this works very well.


Tracing the call to GiveMeAnInt shows 6 calls. Seems like the .ToList
recalls the values so if you want to create the list you would have to put
an ii=0 prior to the .ToList call. My last iteration also removed the need
to have a parameter to the GiveMeAnInt. All in all quite a kludge.

Lloyd Sheen
 
You know, I just realized that I was completely off base with my suggestion.
I haven't actually used Linq (we're still on 2.0), and I was just thinking
that what I was seeing in the OP's code was a simple function call. Clearly
the constructor's being called once for each hit in the select. So my
suggestion wasn't worth a damn.

Sorry 'bout that.

Tom Dacon
 
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