Why is ListBox.Items.IsReadOnly=true? (F#/Silverlight)

Programmer Question

I'm trying to remove some objects from a ListBox that I have created, and for some reason ListBox.Items.IsReadOnly is true.

The following calls don't work:

myListBox.Items.Add("whatever")
myListBox.Items.Add("stuff")
myListBox.Items.Remove("whatever")

I get an exception:

{System.InvalidOperationException: Operation not supported on read-only collection.
   at System.Windows.Controls.ItemCollection.RemoveImpl(Object value)
   at System.Windows.Controls.ItemCollection.RemoveInternal(Object value)
   at System.Windows.PresentationFrameworkCollection`1.Remove(T value)

I can set ListBox.ItemsSource, but working with .Items is much easier. I'm creating the ListBox like this:

let mutable myListBox= new ListBox()

Any ideas/suggestions would be greatly appreciated. Thanks.

Find the answer here