Update Profile After Login

App.xaml.cs

using System;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using ShellDemo.Services;
using ShellDemo.Views;

namespace ShellDemo
{
    public partial class App : Application
    {
        public static string CurrentUserName { get; set; }

        public App()
        {
            InitializeComponent();

            DependencyService.Register<MockDataStore>();
            MainPage = new AppShell();
        }

        protected override void OnStart()
        {
        }

        protected override void OnSleep()
        {
        }

        protected override void OnResume()
        {
        }
    }
}

AppShell.xaml

<?xml version="1.0" encoding="UTF-8"?>
<Shell xmlns="http://xamarin.com/schemas/2014/forms" 
       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
       xmlns:local="clr-namespace:ShellDemo.Views"
       Title="ShellDemo"
       x:Class="ShellDemo.AppShell">

    <!--
        The overall app visual hierarchy is defined here, along with navigation.
    
        https://docs.microsoft.com/xamarin/xamarin-forms/app-fundamentals/shell/
    -->

    <Shell.Resources>
        <ResourceDictionary>
            <Style x:Key="BaseStyle" TargetType="Element">
                <Setter Property="Shell.BackgroundColor" Value="{StaticResource Primary}" />
                <Setter Property="Shell.ForegroundColor" Value="White" />
                <Setter Property="Shell.TitleColor" Value="White" />
                <Setter Property="Shell.DisabledColor" Value="#B4FFFFFF" />
                <Setter Property="Shell.UnselectedColor" Value="#95FFFFFF" />
                <Setter Property="Shell.TabBarBackgroundColor" Value="{StaticResource Primary}" />
                <Setter Property="Shell.TabBarForegroundColor" Value="White"/>
                <Setter Property="Shell.TabBarUnselectedColor" Value="#95FFFFFF"/>
                <Setter Property="Shell.TabBarTitleColor" Value="White"/>
            </Style>
            <Style TargetType="TabBar" BasedOn="{StaticResource BaseStyle}" />
            <Style TargetType="FlyoutItem" BasedOn="{StaticResource BaseStyle}" />
        </ResourceDictionary>
    </Shell.Resources>


    <FlyoutItem Title="Feed"
                FlyoutDisplayOptions="AsMultipleItems">
        <Tab Title="About">
            <ShellContent Title="About" Icon="icon_about.png" Route="AboutPage" ContentTemplate="{DataTemplate local:AboutPage}" />
        </Tab>

        <Tab Title="Browse">
            <ShellContent Title="Browse" Icon="icon_feed.png" ContentTemplate="{DataTemplate local:ItemsPage}" />
        </Tab>

        <Tab Title="Profile">
            <ShellContent Title="Profile" Icon="icon_feed.png" ContentTemplate="{DataTemplate local:ProfilePage}" />
        </Tab>
    </FlyoutItem>
    <!--<TabBar>
        <ShellContent Title="About" Icon="icon_about.png" Route="AboutPage" ContentTemplate="{DataTemplate local:AboutPage}" />
        <ShellContent Title="Browse" Icon="icon_feed.png" ContentTemplate="{DataTemplate local:ItemsPage}" />
    </TabBar>

    <TabBar>
        <ShellContent Route="LoginPage" ContentTemplate="{DataTemplate local:LoginPage}" />
    </TabBar>-->


</Shell>

LoginPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="ShellDemo.Views.LoginPage"
             Shell.TabBarIsVisible="False"
             Shell.NavBarIsVisible="True"
             Shell.PresentationMode="ModalAnimated">
    <ContentPage.Content>
        <StackLayout Padding="10,0,10,0" VerticalOptions="Center">

            <Label Text="Enter Your Username"/>

            <Entry Placeholder="@Username..." Text="{Binding UserName}"/>

            <Button VerticalOptions="Center" Text="Login" Command="{Binding LoginCommand}"/>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

LoginPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ShellDemo.ViewModels;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace ShellDemo.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class LoginPage : ContentPage
    {
        public LoginPage()
        {
            InitializeComponent();
            this.BindingContext = new LoginViewModel();
        }
    }
}

LoginViewModel.cs

using ShellDemo.Views;
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace ShellDemo.ViewModels
{
    public class LoginViewModel : BaseViewModel
    {
        private string userName;
        public string UserName
        {
            get => userName;
            set => SetProperty(ref userName, value);
        }

        public Command LoginCommand { get; }

        public LoginViewModel()
        {
            LoginCommand = new Command(OnLoginClicked);
        }

        private async void OnLoginClicked(object obj)
        {
            var login = await PerformLogin();

            if (!login)
                return;

            await Shell.Current.GoToAsync("..");
        }

        private async Task<bool> PerformLogin()
        {
            if (string.IsNullOrEmpty(userName))
            {
                await Shell.Current.DisplayAlert("Username Required", "Please enter your username to login", "Ok");
                return false;
            }

            App.CurrentUserName = userName;

            return true;
        }
    }
}

ProfilePage.xaml

<?xml version="1.0" encoding="UTF-8" ?>
<ContentPage
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
    x:Class="ShellDemo.Views.ProfilePage">
    <ContentPage.Content>
        <Grid HorizontalOptions="Fill"
              VerticalOptions="Fill"
              xct:StateLayout.CurrentState="Custom"
              xct:StateLayout.CurrentCustomStateKey="{Binding CurrentView}">
            <xct:StateLayout.StateViews>
                <xct:StateView StateKey="Custom" CustomStateKey="LoggedOut">
                    <StackLayout VerticalOptions="Center" HorizontalOptions="Center">
                        <Label Text="Please log in to view your profile"/>
                        <Button Text="Login" Command="{Binding ShowLoginCommand}"/>
                    </StackLayout>
                </xct:StateView>

                <xct:StateView StateKey="Custom" CustomStateKey="LoggedIn">
                    <StackLayout Padding="20" Spacing="20">
                        <Frame HeightRequest="100" WidthRequest="100" BackgroundColor="Orange" HasShadow="False"/>
                        <Label Text="{Binding UserName}" FontSize="Title" FontAttributes="Bold"/>
                        <Label Text="Put some more detail about your profile here"/>
                    </StackLayout>
                </xct:StateView>

            </xct:StateLayout.StateViews>
        </Grid>
    </ContentPage.Content>
</ContentPage>

ProfilePage.xaml.cs

using System;
using System.Collections.Generic;
using ShellDemo.ViewModels;
using Xamarin.Forms;

namespace ShellDemo.Views
{
    public partial class ProfilePage : ContentPage
    {
        private ProfileViewModel viewModel;

        public ProfilePage()
        {
            InitializeComponent();

            viewModel = new ProfileViewModel();

            this.BindingContext = viewModel;
        }

        protected override void OnAppearing()
        {
            if (viewModel.OnAppearingCommand != null &&
                viewModel.OnAppearingCommand.CanExecute(null))
            {
                viewModel.OnAppearingCommand.Execute(null);
            }
        }
    }
}

ProfileViewModel.cs

using System;
using System.Diagnostics;
using ShellDemo.Views;
using Xamarin.Forms;

namespace ShellDemo.ViewModels
{
    public class ProfileViewModel : BaseViewModel
    {
        private string currentView;
        public string CurrentView
        {
            get => currentView;
            set => SetProperty(ref currentView, value);
        }

        private string userName;
        public string UserName
        {
            get => userName;
            set => SetProperty(ref userName, value);
        }

        public Command ShowLoginCommand { get; }

        public Command OnAppearingCommand { get; }

        public ProfileViewModel()
        {
            ShowLoginCommand = new Command(OnShowLogin);
            OnAppearingCommand = new Command(OnAppeared);

            currentView = "LoggedOut";
        }

        async void OnShowLogin()
        {
            Debug.WriteLine("Login");

            await Shell.Current.GoToAsync($"{nameof(LoginPage)}");
        }

        bool IsLoggedIn()
        {
            var userName = App.CurrentUserName;

            return !string.IsNullOrEmpty(userName);
        }

        public void OnAppeared()
        {
            var loggedIn = IsLoggedIn();

            if (loggedIn)
                ShowLoggedIn();
            else
                ShowLoggedOut();
        }

        void ShowLoggedIn()
        {
            UserName = App.CurrentUserName;
            CurrentView = "LoggedIn";
        }

        void ShowLoggedOut()
        {
            CurrentView = "LoggedOut";
        }
    }
}