Fix: Maui Blazor App Initialization Fails With Timezones

by ADMIN 57 views

Hey there, fellow developers! If you're diving into the world of Maui Blazor and running into a snag with application initialization when you're also trying to support multiple timezones, you're in the right place. This article tackles a specific problem: the dreaded error message "Cannot invoke JavaScript outside of a WebView context." This often pops up when your Maui Blazor app tries to initialize the AbpAspNetCoreComponentsMauiBlazorModule and your application is configured to support multiple timezones. We'll explore the root cause, reproduction steps, and a clever workaround that'll get you back on track. Let's jump in!

The Problem: Timezone Initialization Fails

So, what's the deal? You've got a shiny new Maui Blazor app, and you want to make it timezone-aware. Great idea! But when you enable multiple timezone support, the application initialization stumbles. You'll see an exception related to the MauiBlazorCachedApplicationConfigurationClient. It seems the JavaScript runtime is getting invoked prematurely during initialization, outside the context of a WebView, causing the whole thing to crash. The core of the issue lies in how the framework attempts to determine and set the user's timezone.

Specifically, the error occurs when the application tries to interact with the JavaScript runtime before it is fully initialized within the WebView. This often happens when the application tries to get the user's timezone using abp.clock.getBrowserTimeZone. The JavaScript context isn't ready for this call at that stage, leading to the "Cannot invoke JavaScript outside of a WebView context" error.

Deep Dive into the Error

Let's break down the error message a bit further. The key phrase is "Cannot invoke JavaScript outside of a WebView context." In Maui Blazor applications, the .NET code interacts with the web parts using a WebView. This WebView provides the environment for executing JavaScript. The error tells us that an attempt to run JavaScript (like fetching the timezone) is being made before the WebView is fully set up and ready to receive these commands. This typically happens during the early stages of the application's lifecycle, right when the application is trying to initialize.

Steps to Reproduce the Error

Want to see this error for yourself? Here's how to reproduce it:

  1. Create a new ABP solution: Use the ABP CLI to create a new solution, making sure to select Maui Blazor as your UI framework.
  2. Enable Multiple Timezone Support: Configure your application to handle multiple timezones. This usually involves setting up the necessary configurations within your ABP project.
  3. Start the application: Run your Maui Blazor app. Boom! You should see the error. The initialization will fail before the main app UI is fully loaded.

Finding a Workaround

So, what do you do? Fortunately, there's a workaround. The approach involves modifying the MauiBlazorCachedApplicationConfigurationClient to prevent premature JavaScript calls. The key is to postpone the timezone initialization until the WebView is fully ready. This means delaying the call to JSRuntime until the appropriate component initializes.

The Quirky, but Effective Fix

The suggested workaround involves a few steps. It is a great solution, even if it sounds a little bit strange!

  1. Create a custom MauiBlazorCachedApplicationConfigurationClient: You'll need to create a new class that inherits from the original and override the InitializeAsync method. This is a clever way to intercept the initialization process.
  2. Remove Javascript calls: In the override, you'll want to get rid of the calls to the JSRuntime inside the InitializeAsync. We're delaying it to a later point. The code provided in the initial post is great here and can be used almost as is!
  3. Move Timezone Initialization: Instead of initializing the timezone directly in the MauiBlazorCachedApplicationConfigurationClient, the code moves the timezone initialization to a specific component. The example uses a footer component but it could also be used in a MainLayout component, or any other suitable place that is guaranteed to load after the WebView is ready.
  4. Inject and Use: Inject the ICachedApplicationConfigurationClient and IJSRuntime into the component and use them to get the configurations and set up the timezone. The example code provides the InitalizeTimeZone function. This is what you'll call in the OnInitializedAsync lifecycle method.

This approach ensures the JSRuntime is available when the timezone is being set, thus avoiding the error. It postpones the timezone setup to a later stage, allowing the WebView context to be fully set up.

Code Breakdown

Let's break down the code for the custom MauiBlazorCachedApplicationConfigurationClient:

[Volo.Abp.DependencyInjection.Dependency(ReplaceServices = true)]
[ExposeServices(typeof(ICachedApplicationConfigurationClient), typeof(MauiBlazorCachedApplicationConfigurationClient))]
public class MyMauiBlazorCachedApplicationConfigurationClient( 
    AbpApplicationConfigurationClientProxy applicationConfigurationClientProxy, 
    ApplicationConfigurationCache cache, 
    ICurrentTenantAccessor currentTenantAccessor, 
    ICurrentTimezoneProvider currentTimezoneProvider, 
    AuthenticationStateProvider authenticationStateProvider, 
    AbpApplicationLocalizationClientProxy applicationLocalizationClientProxy, 
    ApplicationConfigurationChangedService applicationConfigurationChangedService, 
    IJSRuntime jsRuntime, 
    IClock clock 
) : MauiBlazorCachedApplicationConfigurationClient(applicationConfigurationClientProxy, cache, currentTenantAccessor, currentTimezoneProvider, authenticationStateProvider, applicationLocalizationClientProxy, applicationConfigurationChangedService, jsRuntime, clock) {
    public override async Task InitializeAsync() {
        var configurationDto = await ApplicationConfigurationClientProxy.GetAsync( 
                new ApplicationConfigurationRequestOptions 
                {
                    IncludeLocalizationResources = false 
                } 
            );

        var localizationDto = await ApplicationLocalizationClientProxy.GetAsync( 
            new ApplicationLocalizationRequestDto 
            {
                CultureName = configurationDto.Localization.CurrentCulture.Name, 
                OnlyDynamics = true 
            } 
        );

        configurationDto.Localization.Resources = localizationDto.Resources;

        Cache.Set(configurationDto);

        CurrentTenantAccessor.Current = new BasicTenantInfo(
            configurationDto.CurrentTenant.Id, 
            configurationDto.CurrentTenant.Name);

        ApplicationConfigurationChangedService.NotifyChanged();
    }
}

In this custom client, we override the InitializeAsync method. The key is that we removed the timezone-related Javascript calls here. The primary aim of this modification is to ensure that the application configuration is loaded correctly, without triggering any Javascript before the WebView context is ready.

Now, let's see the footer component example:

[Inject]
protected ICachedApplicationConfigurationClient ApplicationConfigurationClient { get; set; } = default!;

[Inject]
protected IJSRuntime JSRuntime { get; set; } = default!;

[Inject]
protected IClock Clock { get; set; } = default!;

[Inject]
protected ICurrentTimezoneProvider CurrentTimezoneProvider { get; set; } = default!;

private static bool _isTimezoneInitialized;

protected override async Task OnInitializedAsync()
{
    await base.OnInitializedAsync();
    await InitalizeTimeZone();
}

private async Task InitalizeTimeZone()
{
    if (!Clock.SupportsMultipleTimezone || _isTimezoneInitialized)
    {
        return;
    }

    var configuration = await ApplicationConfigurationClient.GetAsync();

    try
    {
        CurrentTimezoneProvider.TimeZone = !configuration.Timing.TimeZone.Iana.TimeZoneName.IsNullOrWhiteSpace()
            ? configuration.Timing.TimeZone.Iana.TimeZoneName
            : await JSRuntime.InvokeAsync<string>("abp.clock.getBrowserTimeZone");

        await JSRuntime.InvokeAsync<string>("abp.clock.setBrowserTimeZoneToCookie");
        _isTimezoneInitialized = true;
    }
    catch
    {
        //ignore
    }
}

In the OnInitializedAsync method, we call the InitalizeTimeZone method. This method fetches the timezone using the JSRuntime. We also add a check to make sure that we only initialize the timezone once.

Conclusion

There you have it! A solid approach to tackle the Maui Blazor application initialization failure when dealing with multiple timezones. By delaying the Javascript calls and putting them in a component lifecycle event, you bypass the error and get your app running. This is a practical workaround. As the ABP framework evolves, the underlying issue might be addressed directly. Until then, this solution should keep your development moving smoothly. Hopefully, this article has been helpful for you guys and gals! Happy coding!