mallibone

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard1.6</TargetFramework>
    <PackageTargetFallback>$(PackageTargetFallback);portable-win+net45+wp8+win81+wpa8</PackageTargetFallback>
  </PropertyGroup>

</Project>

mallibone

public partial class App : Application
{
    public App()
    {
        InitializeComponent();
        var mainPage = new NavigationPage(new MainPage());
        MainPage = mainPage;
    }

    // ....

mallibone

public interface INavigationService
{
    string CurrentPageKey { get; }

    void Configure(string pageKey, Type pageType);
    Task GoBack();
    Task NavigateModalAsync(string pageKey, bool animated = true);
    Task NavigateModalAsync(string pageKey, object parameter, bool animated = true);
    Task NavigateAsync(string pageKey, bool animated = true);
    Task NavigateAsync(string pageKey, object parameter, bool animated = true);

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public class ViewNavigationService : INavigationService
{
    private readonly object _sync = new object();
    private readonly Dictionary<string, Type> _pagesByKey = new Dictionary<string, Type>();
    private readonly Stack<NavigationPage> _navigationPageStack =
        new Stack<NavigationPage>();
    private NavigationPage CurrentNavigationPage => _navigationPageStack.Peek();

    public void Configure(string pageKey, Type pageType)
    {

mallibone

public partial class App : Application
{
    public App()
    {
        InitializeComponent();

        NavigationService.Configure("MainPage", typeof(Views.MainPage));
        NavigationService.Configure("ModalNavigationPage", typeof(Views.ModalNavigationPage));
        NavigationService.Configure("PushNavigationPage", typeof(Views.PushNavigationPage));
        var mainPage = ((ViewNavigationService) NavigationService).SetRootPage("MainPage");

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await _navigationService.NavigateAsync("PushNavigationPage", "simple string parameter");

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<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="LoginViewSample.Core.Views.LoginPage">
    <ContentPage.Content>
        <Grid Margin="16">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
                <RowDefinition Height="Auto"/>

mallibone

using System.ComponentModel;
using System.Windows.Input;
using LoginViewSample.Core.Services;
using Xamarin.Forms;

namespace LoginViewSample.Core.ViewModels
{
    public class LoginViewModel : INotifyPropertyChanged
    {
        private string _username;

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private void Logout()
{
    _navigationService.NavigateModalAsync(PageNames.LoginPage);
}

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protected override bool OnBackButtonPressed()
{
    return true;
}