Problem instantiating Tab page Child Viewmodel with Prism NavigationService - xamarin.forms

Question

We have managed to wire a child content page of a tab page to its own viewmodel in our Prism Xamarin Forms app. This works if ContactsScreenViewModel has a parameterless constructor. If we inject the NavigationService into the constructor the code doesn't compile. Does anyone know how we can solve this problem?
Visual Studio is reporting that a parameterless constructor is required
<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:views="clr-namespace:TabsTest.Views"
xmlns:viewmodels="clr-namespace:TabsTest.ViewModels"
x:Class="TabsTest.Views.MainPage"
Title="{Binding Title}"
UnselectedTabColor ="Gray"
SelectedTabColor="Green"
BarBackgroundColor="LightGray">
<views:ContactsScreen BackgroundColor="White" Title="Contacts">
<views:ContactsScreen.BindingContext>
<viewmodels:ContactsScreenViewModel/>
</views:ContactsScreen.BindingContext>
<ContentPage.ToolbarItems>
<ToolbarItem Order="Primary"
Priority="1" >
</ToolbarItem>
<ToolbarItem Order="Primary"
Priority="0" >
</ToolbarItem>
</ContentPage.ToolbarItems>
</views:ContactsScreen>
</TabbedPage>
using Prism.Navigation;
using System;
using System.Collections.Generic;
using System.Text;
namespace TabsTest.ViewModels
{
public class ContactsScreenViewModel
{
private INavigationService _navigationService { get; }
public ContactsScreenViewModel(INavigationService navigationService)
{
_navigationService = navigationService;
}
}
}

Answer 1

<viewmodels:ContactsScreenViewModel/> is a constructor call... where do you expect the parameters to come from?
You want to either resolve the view model first (through a factory) and then attach the view to it, or make use of the ViewModelLocator to resolve the view model for you (and resolve and inject its dependencies) as described here, for example.
<TabbedPage [...]
xmlns:prism="http://prismlibrary.com"
prism:ViewModelLocator.AutowireViewModel="True">
will resolve an instance of TabbedPageViewModel and put it the BindingContext.
That one should expose an instance of ContactsScreenViewModel through a property:
<views:ContactsScreen BindingContext={Binding ThePropertyOnTabbedPageViewModel}/>
You create that instance to your liking, with all parameters and dependencies you need.