Jason Bock

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foreach And Skipping Objects

Hmmm. I always thought foreach in C# and For Each in VB .NET would return objects of the specified type and skip over ones that don’t match. I should’ve read the documentation. Consider the following code:

ArrayList al = new ArrayList();
al.Add(new Guid());
al.Add(new Random());
al.Add(new Guid());
al.Add(new Random());
al.Add(new Guid());
al.Add(new Random());
al.Add(new Guid());
al.Add(new Random());

foreach(Guid g in al)
{
  Console.WriteLine("Found a Guid object.");
}

It will throw an InvalidCastException. I know how to get around this - here’s some code in VB .NET to illustrate:

Dim oGUIDs As IEnumerator = al.GetEnumerator()

Do While oGUIDs.MoveNext()
  If TypeOf oGUIDs.Current Is Guid Then
    Dim aGUID as Guid = CType(oGUIDs.Current, Guid)
    '  Do something with aGuid...
  End If
Loop

So much for assuming!

Published: 07.10.2002 10:30:00 AM CST

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