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XAML: A canvas, I have a few buttons and rectangles.

Challenge: Remove the rectangles from the Canvas using only their types, but leaving the existing buttons alone.

Thoughts: I've wondered if this is possible with LINQ, but I'm stupid green to LINQ.  I have seen LINQ used to query an SQL database and XML, but I've never seen an example of it tweaking XAML objects.  I'm thinking it's theorically possible.

Discoveries: 

I've discovered:

1. I can loop through all of the elements in a Canvas by referencing its "Children". 

2. I can use the "GetType" method to find an element's type.

3. Calling the "Remove" method of a Canvas inside of a foreach loop throws the program into an error.

You can't remove items from a collection when you are iterating the collection.  Instead, make a list of the items references, then iterate from the new list and remove them. 

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles Button1.Click

    Debug.WriteLine("Before: " & Me.cnvRoot.Children.Count)

    Dim objRemoveList As New List(Of Rectangle)

    For Each objRectangle As Rectangle In From r In Me.cnvRoot.Children Where TypeOf r Is Rectangle Select CType(r, Rectangle)

        objRemoveList.Add(objRectangle)

    Next

    For Each objRectangle In objRemoveList

        Me.cnvRoot.Children.Remove(objRectangle)

    Next

    objRemoveList.Clear()

    objRemoveList = Nothing

    Debug.WriteLine("After: " & Me.cnvRoot.Children.Count)

End Sub