Clearing dropdown selection

Hi,

I currently have a panel like the picture above, which allows users to type in a new building name and select a site from a dropdown list and add it to the database.

After the user clicks the 'Add' button, both the Building name textfield and the Sitename dropdown list should be emptied out. Right now, when a user clicks Add, the Building name textfield becomes empty (I did it binding the textfield to a property and writing a service that changes the property to '  '). But, it does not empty the dropdown list. I have tried using the same method I used for the textfield like binding a property to the selectedText feature of the dropdownlist and setting that to ' ', but this doesn't seem to work for the dropdown widget.

How can I achieve this?

Thank you!