You could easily achieve the desired by finding the WatermarkTextBox inside of the AutoCompleteBox and setting its HorizontalContentAlignment property to Right. You could do that when Loaded event of the AutoCompleteBox is fired, the handler should like as follows:
sender, RoutedEventArgs e)
var watermark =
watermark.HorizontalContentAlignment = System.Windows.HorizontalAlignment.Right;
However this will cause the text input when typing to also go on the right side, so what you can do is to set it back to Left on GotFocus event of the AutoComplete and set it back to Right on LostFocus. I have prepared and attached a sample project which demonstrates the exact approach.
Hope this helps.
TRY TELERIK'S NEWEST PRODUCT - EQATEC APPLICATION ANALYTICS for WPF.
Learn what features your users use (or don't use) in your application. Know your audience. Target it better. Develop wisely.
Sign up for Free application insights >>