Setting a XAML Icon to show an activity indicator when clicked

Hi,

I have an icon on my app, which when it is clicked, I would like to change it to an activity indicator. It looks as though I should use a Trigger, Event Triggers look good, but as my image is declared in XAML, I am not sure quite how it would fit together?

At the moment, I have this in XAML:

      <Button x:Name="NewDeviceButton" 
                Image="glyphish_31_circle_x.png" 
                HorizontalOptions="End"
                VerticalOptions="EndAndExpand" />

When it is clicked, I would like to show this, for a set amount of time, then trigger some C# functionality:

<ActivityIndicator Color="Black" IsRunning="true" />

How would I best structure this?