Catch exception in iteration of ContextMenuStrip items - vb.net

Question

I'm trying to iterate over contextmenustrip items like this:
Public Sub TranslateContextMenuStrip(ByRef u As ContextMenuStrip)
For Each t As ToolStripMenuItem In u.Items 'here the error occurs
pProcessMenuItem(t) 'not here
Next
End Sub
But I have toolstrip separators in the contextmenustrip, and I'm getting the error
"System.InvalidCastException: The object of type System.Windows.Forms.ToolStripSeparator can't be converted to type System.Windows.Forms.ToolStripMenuItem"
as soon as it stumbles over a separator.
I wonder why this separator is included in items (I am requesting "For Each t As ToolStripMenuItem" so why does it return non-ToolStripMenuItems???) and how to catch this error or avoid it.

Answer 1

I found a solution, but not the problem:
For Each it As Object In u.Items
If TypeOf it Is ToolStripMenuItem Then
pProcessMenuItem(it)
End If
Next

Answer 2

I dont think For Each t As ToolStripMenuItem does what you might think it does.
It simply declares that the t iterator will be of Type ToolStripMenuItem. It does nothing to the item collection itself. When you come to seperator, you get the cast exception because a separator cannot be converted to a menu item.
Items is a collection of ToolStripItems. This is a base class used for all the Types a context menu can hold (menu item, combo, text box or separator). Since these all inherit from ToolStripItem the collection can hold any of them (specifically, a ToolStripSeparator item is also a ToolStripItem)
There are several ways to iterate or work with just the menu entries:
Filter the Items collection
For Each tsi As ToolStripMenuItem In u.Items.OfType(Of ToolStripMenuItem)()
' do something fun with tsi
Next
The OfType() extension filters the items collection to just menu items.
This is by far the simplest because your iterator tsi is the proper type. This is particularly true if your method is writen to expect menu items:
Sub pProcessMenuItem(item As ToolStripMenuItem)
The tsi iterator is same Type expected by the method, so no further steps are needed. Anything else will require casting either in the method or to call the method (or Option Strict Off).
Test the Type:
' iterate all the items
For Each tsi As ToolStripItem In u.Items
' test the type of each
If TypeOf tsi Is ToolStripMenuItem Then
' do something fun with tsi
End If
Next
Under Option Strict passing tsi to a method declared as shown above wont compile. You would have to cast before invoking your method:
pProcessMenuItem(CType(tsi, ToolStripMenuItem))
If the method is declared to accept a ToolStripItem or Object, the cast would have to take place in the method if you need to access any menu related properties.
The same is true using As Object to iterate:
For Each it As Object In u.Items
If TypeOf it Is ToolStripMenuItem Then
pProcessMenuItem(it)
End If
Next
The only way this will compile under Option Strict if the method argument is declared As Object. As above, Object may have to be cast to ToolStripMenuItem. The first method prevents any need for this.