MainPage.xaml

<Picker Title="Choose Country
         SelectedItem="{Binding SelectedCountryFilter}">
        <Picker.Items>
            <x:String>All</x:String>
               <x:String>United States</x:String>
               <x:String>Venezuela</x:String>
               <x:String>Dominican Republic</x:String>
                <x:String>Colombia</x:String>
         </Picker.Items>
</Picker>

<SearchBar Text="{Binding SearchText}" />
<ListView  x:Name="RestaurantsList"
           ItemsSource="{Binding Restaurants}">
    ...
</ListView>