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| Title | Bug: For Each loop in VB .NET doesn't end with variable equal to Nothing |
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| Keywords | bug, loop, for each, ForEach, VB.NET |
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| Categories | Bug Alerts, VB.NET |
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In VB 6, you can use code similar to the following to see if an object is in a collection.
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For Each obj In values
If obj.value = target_value Then Exit For
Next obj
If obj Is Nothing Then
MsgBox "Not found"
Else
MsgBox "Found"
End If
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In VB .NET, if the target object doesn't appear in the collection the For Each loop finishes with the looping variable pointing to the last item in the collection. That means this code always thinks it has found the target object.
[Actually most languages including VB say that the value of the looping variable is not defined at the end of the loop and that you should not rely on it having a particular value. That's certainly the case here.]
Here's one way around this problem.
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Dim obj As Object
Dim found_it As Object
found_it = Nothing
For Each obj In values
If obj = txtValue.Text Then
found_it = obj
Exit For
End If
Next obj
If found_it Is Nothing Then
lblFoundIt.Text = "Not found"
Else
lblFoundIt.Text = "Found"
End If
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