.NET MAUI, how to get data from SecureStorage in constructor

Question

I am struggling to get JWT from SecureStorage, as it's Get method is async, and we all know that constructor doesn't support async calls.

UPDATE:

What I want to do is check if I have a token and at the app start show the LoginPage or the MainPage.

I tried something like this:

public AppShell()
    {
        JWTokenModel jwt = null;
        Task.Run(async () =>
        {
            jwt = await StorageService.Secure.GetAsync<JWTokenModel>(StorageKeys.Secure.JWT);
        });

        InitializeComponent();
        RegisterRoutes();

        shellContent.Title = "Amazons of Volleyball";

        if (jwt is null || jwt?.Expiration < DateTime.Now)
        {
            shellContent.Route = PageRoutes.LoginPage;
            shellContent.ContentTemplate = new DataTemplate(typeof(LoginPage));
        }
        else
        {
            shellContent.Route = PageRoutes.HomePage;
            shellContent.ContentTemplate = new DataTemplate(typeof(MainPage));
        }
    }

    private void RegisterRoutes()
    {
        Routing.RegisterRoute(PageRoutes.LoginPage, typeof(LoginPage));
        Routing.RegisterRoute(PageRoutes.HomePage, typeof(MainPage));
        Routing.RegisterRoute(PageRoutes.DetailsPage, typeof(PlayerDetailsPage));
        Routing.RegisterRoute(PageRoutes.AddOrUpdatePage, typeof(AddOrUpdatePlayer));
    }

When it hits the StorageService.Secure.GetAsync method's line, where I wan't to get the data like

public static async Task<T> GetAsync<T>(string key)
{
    try
    {
        var value = await SecureStorage.Default.GetAsync(key);

        if (string.IsNullOrWhiteSpace(value))
            return (T)default;

        var data = JsonSerializer.Deserialize<T>(value);
        return data;
    }
    catch(Exception ex)
    {
        return (T)default;
    }
}

it simple jumps out of the method.

UPDATE: I update the code suggested by ewerspej. The error still stands, when the SecureStore tries to get the value it jumps out from the method, no exception and I got the following error:

System.InvalidOperationException: 'No Content found for ShellContent, Title:, Route D_FAULT_ShellContent2'

The updated code:

public partial class AppShell : Shell
{
    public AppShell()
    {
        InitializeComponent();
        RegisterRoutes();

        SetShellContentTemplate();
    }

    private async void SetShellContentTemplate()
    {
        var hasValidJWT = await LoadTokenAsync();

        if (hasValidJWT)
        {
            shellContent.ContentTemplate = new DataTemplate(typeof(MainPage));
            shellContent.Route = PageRoutes.HomePage;
            shellContent.Title = "Amazons of Volleyball";
        }
        else
        {
            shellContent.ContentTemplate = new DataTemplate(typeof(LoginPage));
            shellContent.Route = PageRoutes.LoginPage;
            shellContent.Title = "Amazons of Volleyball";
        }
    }

    private async Task<bool> LoadTokenAsync()
    {
        var jwt = await StorageService.Secure.GetAsync<JWTokenModel>(StorageKeys.Secure.JWT);

        return !(jwt is null || jwt?.Expiration < DateTime.Now);
    }

    private void RegisterRoutes()
    {
        Routing.RegisterRoute(PageRoutes.LoginPage, typeof(LoginPage));
        Routing.RegisterRoute(PageRoutes.HomePage, typeof(MainPage));
        Routing.RegisterRoute(PageRoutes.DetailsPage, typeof(PlayerDetailsPage));
        Routing.RegisterRoute(PageRoutes.AddOrUpdatePage, typeof(AddOrUpdatePlayer));
    }
}

UPDATE 2: Moved the logic to App class:

public static class PageRoutes
{
    public static string LoginPage = "login";
    public static string HomePage = "home";
    public static string AddOrUpdatePage = "add-or-update";
    public static string DetailsPage = "/details";
}

public partial class App : Application
{
    private readonly ISecurityClient securityClient;

    public App(ISecurityClient securityClient)
    {
        this.securityClient = securityClient;

        InitializeComponent();
        SetStartPage();
    }

    private async void SetStartPage()
    {
        var hasValidJWT = await ReatJwtAsync();

        MainPage = hasValidJWT ?
                              new AppShell() :
                              new LoginPage(securityClient);
    }

    private async Task<bool> ReatJwtAsync()
    {
        var jwt = await StorageService.Secure.GetAsync<JWTokenModel>(StorageKeys.Secure.JWT);

        return !(jwt is null || jwt?.Expiration < DateTime.Now);
    }
}

public partial class AppShell : Shell
{
    public AppShell()
    {
        RegisterRoutes();
        InitializeComponent();
    }

    private void RegisterRoutes()
    {
        Routing.RegisterRoute(PageRoutes.LoginPage, typeof(LoginPage));
        Routing.RegisterRoute(PageRoutes.HomePage, typeof(MainPage));
        Routing.RegisterRoute(PageRoutes.DetailsPage, typeof(PlayerDetailsPage));
        Routing.RegisterRoute(PageRoutes.AddOrUpdatePage, typeof(AddOrUpdatePlayer));
    }
}

AppShell.xaml

<?xml version="1.0" encoding="UTF-8" ?>
<Shell
    x:Class="MauiUI.AppShell"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:local="clr-namespace:MauiUI"
    xmlns:pages="clr-namespace:MauiUI.Pages"
    Shell.FlyoutBehavior="Disabled">

    <ShellContent
        Title="Amazons of Volleyball"
        ContentTemplate="{DataTemplate local:MainPage}"
        Route="HomePage" />

</Shell>

Still not reading a token successfully. But looking at the output I can see that Thread #8 started (might have some impact). Now I am getting a new error:

System.NotImplementedException: 'Either set MainPage or override CreateWindow.'

any idea? thnx

Answer 1

Instead of loading the token directly inside the constructor, you should defer it to an asynchronous method which you can still call from within the constructor, but you cannot await it and you shouldn't be using a blocking call, either.

You could do this in the App.xaml.cs, which is a common place for loading data when an app starts. While the data is loading, you can set the MainPage object to some type of loading page and once the token was loaded, you can set the MainPage to the AppShell or a LoginPage instance, e.g. like this:

public App()
{
    InitializeComponent();

    MainPage = new LoadingPage();

    Load();
}

private async void Load()
{
    if (await LoadTokenAsync())
    {
        MainPage = new AppShell();
    }
    else
    {
        MainPage = new LoginPage();
    }
}

private async Task<bool> LoadTokenAsync()
{
    var jwt = await StorageService.Secure.GetAsync<JWTokenModel>(StorageKeys.Secure.JWT);

    return !(jwt is null || jwt?.Expiration < DateTime.Now);
}

This is just to demonstrate how you could solve the problem. You shouldn't do this in AppShell.xaml.cs but rather in the App.xaml.cs. Obviously, you'll need to store the token in memory somewhere.