Enumeration in vb.net - vb.net

Question

while executing this below lines i got an error. Error:
Collection was modified; enumeration operation may not execute.
Help me to solve this.
Dim i As IEnumerator
Dim item As DataGridItem
Dim bChk As Boolean = False
i = dgOfferStatus.Items.GetEnumerator
For Each item In dgOfferStatus.Items
i.MoveNext()
item = i.Current
item = CType(i.Current, DataGridItem)
Dim chkItemChecked As New CheckBox
chkItemChecked = CType(item.FindControl("chkItemChecked"), CheckBox)
If chkItemChecked.Checked = True Then
Try
bChk = True
lo_ClsInterviewProcess.JobAppID = item.Cells(1).Text
lo_ClsInterviewProcess.candId = item.Cells(9).Text
Dim str, strSchedule1, strSchedule As String
Dim dspath As DataSet
Dim candidateId As Integer
''Moving the resume to Completed folder
ObjInterviewAssessment = New ClsInterviewAssessment
dspath = ObjInterviewAssessment.GetOffComPath(CInt(lo_ClsInterviewProcess.JobAppID), "GetHoldPath")
If dspath.Tables(0).Rows.Count > 0 Then
If Not IsDBNull(dspath.Tables(0).Rows(0).Item(0)) Then
str = dspath.Tables(0).Rows(0).Item(0)
strSchedule1 = str.Replace("Hold", "Completed")
End If
End If
Dim str1 As String
str1 = Server.MapPath(str).Trim
strSchedule = Server.MapPath(strSchedule1).Trim
Dim file1 As File
If file1.Exists(str1) Then
If file1.Exists(strSchedule) Then
file1.Delete(strSchedule)
End If
file1.Move(str1, strSchedule)
End If
''
intResult = lo_ClsInterviewProcess.UpdateApproveStatus(Session("EmployeeId"), strSchedule1)
BindHoldGrid()
If intResult > 0 Then
Alert.UserMsgBox("btnsearch", "Status Updated")
Else
Alert.UserMsgBox("btnsearch", "Status not Updated")
End If
Catch ex As Exception
ExceptionManager.Publish(ex)
Throw (ex)
End Try
End If
Next
If bChk = False Then
Alert.UserMsgBox("btnsearch", "Please Select any Candidate")
End If
'Catch ex As Exception
' ExceptionManager.Publish(ex)
'End Try
End Sub

Answer 1

Look at this part of your code. I think it's what causes your exception.
Dim i As IEnumerator
...
Dim item As DataGridItem
...
i = dgOfferStatus.Items.GetEnumerator
For Each item In dgOfferStatus.Items
i.MoveNext()
item = i.Current ' <-- here be dragons!? '
...
Next
What you're doing seems a little strange. You iterate through the same collection (dgOfferStatus.Items) twice, once with the For Each loop, and once manually using the i iterator. Then you modify items in your collection with item = i.Current. I believe it's this assignment that causes the exception.
(I also don't understand why you would do this. This assignment seems to be completeley superfluous, since i.Current and item should be identical since both iterators are at the same position in the collection.)
The exception basically tries to tell you that you may not modify a collection while you are iterating through it. But you seem to be doing exactly that.