Hi Francesco,

Thank you for sending this feature request.

With the new R3 2018 release of Telerik UI for Xamarin we shipped RadAutoCompleteView control that provides remote search functionality, you could learn more about the component at the links below:
https://docs.telerik.com/devtools/xamarin/controls/autocompleteview/autocompleteview-overview
https://docs.telerik.com/devtools/xamarin/controls/autocompleteview/autocompleteview-remote-search

As to its position in the navigation bar - this is more of application logic, for example, you could check our SDKBrowser application (https://docs.telerik.com/devtools/xamarin/sdk-browser-overview) where there is a search field in the navigation bar - this is implemented by modifying the ControlTemplate of the ContentPage.  If you download the SDKBrowser app, you could check the App.xaml of the portable project for the exact approach. 

I believe RadAutoCompleteView will be suitable for achieving the described scenario, so I've updated the status of this item to "Declined".

Let me know if you have any additional questions or concerns.

Regards,
Yana