I understand you concern. However could you please share some more details about the exact requirements for the chat implementation? Do you really need to have selection there, as if not you could use a simple ItemsControl instead of the ListBox?
Also what I can suggest you would be not to replace the whole ItemsSource every time you add items, but use ObesrvableCollection
instead and simply add the items to it. The ObservableCollection will notify the UI and the new items will show up. Afterwards you can simply scroll to the last one using the ListBox ScrollIntoView method.
I'm looking forward to your response.
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