SyncLock Required Before If Statement Or For Loop?

If completedOrders.Count <> 0 Then
For i = 0 To completedOrders.Count - 1
SyncLock completedOrders
'Do some work, for example this:
Dim text As String = completedOrders(0).getCN & " " & completedOrders(0).getDeviceName & " "
End SyncLock
Next
End If
Is a synclock needed before the if statement or for loop? In other words. When you call methods like .length or .count is it necessary to synclock them or can another thread be writing to it at the same time. CompletedOrders is a generic list of a class.