CODEWITHSUNDEEP
vb.netlambda
Saif Khan
Saif Khan

Reputation: 18812

What's the deal with this Lambda?

Dim count As Func(Of Integer, Boolean) = Function(x As Integer) x = 1

If (count(GetSelectedCount())) Then
    'Proceed
Else
    MessageBox.Show("You can only select one item at a time.", "Multiple items selected", MessageBoxButtons.OK)
End If

GetSelectedCount returns the number of items checkemarked in a grid. It returns 0 when nothing is selected. The Lambda is supposed to return true only when 1 item is selected. The messagebox should only run when > 1 items are selected. I ma getting the messagebox even when no items are selected.

Solution ~ Decided to drop the Lambda and go old school

Select Case GetSelectedCount()
    Case 1

    Case Is > 1
        MessageBox.Show("You can only select one item at a time.", "Multiple Selection", MessageBoxButtons.OK)
    Case Else
        MessageBox.Show("You have no items selected.", "No Selection", MessageBoxButtons.OK)

End Select

Upvotes: 0

Views: 175

Answers (2)

Eric
Eric

Reputation: 11662

Your lambda function (checks whether ONE item is selected) and your stated goal (run message box if >1 items are selected) are not mutually exclusive. Neither covers the case when NO items are selected.

So if no items are selected, then "x=1" is false, so the "If" statement fails and you fall through to the message box.

What about writing

Dim count As Func(Of Integer, Boolean) = Function(x As Integer) (x <= 1)

??

Upvotes: 2

Joel Coehoorn
Joel Coehoorn

Reputation: 416149

The = operator pulls double duty for both assignment and equality in VB.Net. Is it possible it's being interpreted incorrectly as assignment here? Try this instead:

Dim count As Func(Of Integer, Boolean) = Function(x As Integer) Return x = 1

Upvotes: 2

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