Blazor in .NET 9

When Microsoft introduced Blazor, it revolutionized how .NET developers approach web development. With .NET 9, Blazor takes another significant leap forward, introducing features and improvements that make web development more efficient and enjoyable. Let's explore these changes and understand how they transform the way we build web applications.

Seamless Server-Side Reconnection

One of the most significant improvements in Blazor .NET 9 is the enhanced server-side reconnection system. In previous versions, when a user's browser tab went to sleep or lost connection, resuming the session could be problematic. The new system handles these scenarios much more gracefully.

Here's how the improved reconnection system works:

public class Program
{
    public static void Main(string[] args)
    {
        var builder = WebApplication.CreateBuilder(args);
        
        // Configure enhanced reconnection settings
        builder.Services.AddBlazorServerOptions(options =>
        {
            // New in .NET 9: Configurable retry strategies
            options.DisconnectedCircuitRetention = TimeSpan.FromMinutes(30);
            options.MaxRetryAttempts = 3;
            options.ReconnectionPolicy = new ExponentialBackoffPolicy
            {
                InitialDelayMilliseconds = 1000,
                MaxDelayMilliseconds = 10000,
                JitterFactor = 0.1
            };
        });
        
        // Configure client-side recovery
        builder.Services.AddCircuitHandler<CustomCircuitHandler>();
    }
}

public class CustomCircuitHandler : CircuitHandler
{
    private readonly ILogger<CustomCircuitHandler> _logger;
    private readonly IStateService _stateService;

    public CustomCircuitHandler(
        ILogger<CustomCircuitHandler> logger,
        IStateService stateService)
    {
        _logger = logger;
        _stateService = stateService;
    }

    public override Task OnConnectionUpAsync(Circuit circuit)
    {
        _logger.LogInformation("Circuit {CircuitId} reconnected", circuit.Id);
        return _stateService.RestoreUserStateAsync(circuit.Id);
    }
}        

This new system provides several advantages:

1. Automatic state preservation during disconnections
2. Configurable retry strategies with exponential backoff
3. Improved user experience with seamless session recovery
4. Better handling of mobile device scenarios

Enhanced Interactive Components

Blazor .NET 9 introduces a more powerful component model that combines the best aspects of server-side and client-side rendering. Here's an example of a modern interactive component:

public partial class DataGrid<TItem> : ComponentBase
{
    [Parameter]
    public IEnumerable<TItem> Items { get; set; } = default!;

    [Parameter]
    public RenderFragment<TItem> RowTemplate { get; set; } = default!;

    // New in .NET 9: Enhanced state management
    private PersistentComponentState _persistentState;

    // New in .NET 9: Streaming rendering support
    private IAsyncEnumerable<TItem> _streamingItems;

    protected override async Task OnInitializedAsync()
    {
        // Implement streaming rendering
        _streamingItems = GetItemsAsStream();
        await foreach (var item in _streamingItems)
        {
            // Progressive rendering of items
            StateHasChanged();
        }
    }

    private async IAsyncEnumerable<TItem> GetItemsAsStream()
    {
        foreach (var item in Items)
        {
            // Simulate network delay for demonstration
            await Task.Delay(100);
            yield return item;
        }
    }
}        

This improved component model offers:

1. Better performance through streaming rendering
2. Enhanced state management capabilities
3. More flexible templating options
4. Improved interaction with JavaScript

WebAssembly Optimization

Blazor .NET 9 brings significant improvements to WebAssembly performance. The new ahead-of-time (AOT) compilation process is more efficient and produces smaller output:

public class WebAssemblyStartup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddBlazorWebAssembly(options =>
        {
            // New in .NET 9: Enhanced AOT settings
            options.EnableAotCompilation = true;
            options.WasmOptimizationLevel = WasmOptimizationLevel.Size;
            options.EnableWebAssemblyDebugging = 
                !Environment.GetEnvironmentVariable("RELEASE_MODE").Equals("true");
        });
    }
}        

The optimization improvements result in:

1. Faster initial loading times
2. Reduced memory usage
3. Better runtime performance
4. Improved debugging experience

Enhanced Form Handling

Form handling in Blazor .NET 9 becomes more intuitive and powerful with new built-in features:

public partial class AdvancedForm : ComponentBase
{
    private EditContext _editContext;
    private ValidationMessageStore _messageStore;
    private readonly CustomerModel _model = new();

    // New in .NET 9: Enhanced validation support
    protected override void OnInitialized()
    {
        _editContext = new EditContext(_model);
        _messageStore = new ValidationMessageStore(_editContext);

        _editContext.OnValidationRequested += (sender, args) =>
        {
            _messageStore.Clear();
            // Custom validation logic
            if (string.IsNullOrEmpty(_model.Email))
            {
                _messageStore.Add(() => _model.Email, "Email is required");
            }
        };

        _editContext.OnFieldChanged += (sender, args) =>
        {
            // Real-time validation as user types
            ValidationRequestedEventArgs.Empty.Invoke(_editContext);
        };
    }

    private async Task HandleValidSubmit()
    {
        // New in .NET 9: Improved form submission handling
        try
        {
            var response = await SubmitFormData(_model);
            if (response.IsSuccess)
            {
                // Handle success
            }
        }
        catch (Exception ex)
        {
            // Enhanced error handling
            _messageStore.Add(() => _model, "An error occurred while submitting the form");
        }
    }
}        

The new form-handling features provide:

1. More precise validation control
2. Better error handling
3. Improved user feedback
4. Enhanced form state management

Performance Monitoring and Debugging

Blazor .NET 9 introduces new tools for monitoring and debugging applications:

public class Program
{
    public static void Main(string[] args)
    {
        var builder = WebApplication.CreateBuilder(args);

        // New in .NET 9: Enhanced diagnostics
        builder.Services.AddBlazorDiagnostics(options =>
        {
            options.DetailedErrors = builder.Environment.IsDevelopment();
            options.CircuitDetailedErrors = true;
            options.EnablePerformanceTracing = true;
        });

        // Configure OpenTelemetry integration
        builder.Services.AddOpenTelemetry()
            .WithTracing(tracing =>
            {
                tracing.AddBlazorInstrumentation()
                    .SetSampler(new AlwaysOnSampler());
            })
            .WithMetrics(metrics =>
            {
                metrics.AddBlazorMetrics();
            });
    }
}        

These improvements help developers:

1. Identify performance bottlenecks
2. Debug complex interactions
3. Monitor application health
4. Optimize user experience

Best Practices and Recommendations

When working with Blazor .NET 9, consider these practices for optimal results:

1. Component Design:

public partial class OptimizedComponent : ComponentBase
{
    // Use memory efficiently
    private readonly System.Buffers.ArrayPool<byte> _arrayPool = 
        System.Buffers.ArrayPool<byte>.Shared;

    // Implement IAsyncDisposable for cleanup
    public async ValueTask DisposeAsync()
    {
        // Clean up resources
        await CleanupResourcesAsync();
        GC.SuppressFinalize(this);
    }

    // Use cascading parameters efficiently
    [CascadingParameter]
    private Task<AuthenticationState> AuthState { get; set; }

    protected override async Task OnInitializedAsync()
    {
        var user = (await AuthState).User;
        // Initialize based on user state
    }
}        

2. State Management:

public class StateContainer
{
    private readonly Dictionary<string, object> _state = new();
    
    public T GetState<T>(string key)
    {
        if (_state.TryGetValue(key, out var value))
        {
            return (T)value;
        }
        return default;
    }
    
    public void SetState<T>(string key, T value)
    {
        _state[key] = value;
        NotifyStateChanged();
    }
    
    public event Action OnStateChange;
    private void NotifyStateChanged() => OnStateChange?.Invoke();
}        

Conclusion

Blazor in .NET 9 represents a significant evolution in web development capabilities. The improvements in reconnection handling, component model, WebAssembly performance, and development tools make it an even more compelling choice for building modern web applications. Whether you're creating a new application or maintaining an existing one, these enhancements provide the tools needed for success in today's web development landscape.