.NET 9 Blazor：Blazor Unitedによるフルスタック開発ガイド 2026年版

# Create a new Blazor Web App with all render modes enabled
dotnet new blazorweb -n FullStackApp --interactivity Auto --all-interactive false
cd FullStackApp
dotnet run

@page "/dashboard"
@rendermode InteractiveServer

<PageTitle>Dashboard</PageTitle>

<h1>Real-Time Metrics</h1>

<!-- This component renders interactively via SignalR -->
<MetricsChart />

<!-- Static content below renders as plain HTML -->
<footer>Updated every 5 seconds</footer>

@if (RendererInfo.IsInteractive)
{
    <button @onclick="HandleClick">Interactive Action</button>
}
else
{
    <a href="/fallback">Static Fallback Link</a>
}

@code {
    private void HandleClick()
    {
        // Runs only in interactive modes (Server or WASM)
    }
}

@page "/products"
@attribute [StreamRendering]

<PageTitle>Product Catalog</PageTitle>

@if (products is null)
{
    <p>Loading products...</p>
}
else
{
    <div class="product-grid">
        @foreach (var product in products)
        {
            <ProductCard Item="@product" />
        }
    </div>
}

@code {
    private List<Product>? products;

    // Data loads asynchronously; streaming pushes updates to the browser
    protected override async Task OnInitializedAsync()
    {
        products = await ProductService.GetAllAsync();
    }
}

@page "/orders"
@rendermode InteractiveServer

<h2>Order History</h2>

@if (orders is not null)
{
    <table>
        <thead>
            <tr><th>Order ID</th><th>Date</th><th>Total</th></tr>
        </thead>
        <tbody>
            @foreach (var order in orders)
            {
                <tr>
                    <td>@order.Id</td>
                    <td>@order.PlacedAt.ToShortDateString()</td>
                    <td>@order.Total.ToString("C")</td>
                </tr>
            }
        </tbody>
    </table>
}

@code {
    // Constructor injection via primary constructor
    [Inject] public required IOrderService OrderService { get; set; }
    [Inject] public required NavigationManager Nav { get; set; }

    private List<Order>? orders;

    protected override async Task OnInitializedAsync()
    {
        orders = await OrderService.GetRecentOrdersAsync();
    }
}

@page "/chat"
@rendermode InteractiveAuto

<h2>Live Chat</h2>

<div class="chat-messages">
    @foreach (var msg in messages)
    {
        <div class="message">@msg.Author: @msg.Text</div>
    }
</div>

<input @bind="newMessage" @onkeydown="HandleKey" placeholder="Type a message..." />

@code {
    [Inject] public required IChatService ChatService { get; set; }

    private List<ChatMessage> messages = new();
    private string newMessage = string.Empty;

    protected override async Task OnInitializedAsync()
    {
        messages = await ChatService.GetRecentMessagesAsync();
    }

    private async Task HandleKey(KeyboardEventArgs e)
    {
        if (e.Key == "Enter" && !string.IsNullOrWhiteSpace(newMessage))
        {
            await ChatService.SendAsync(newMessage);
            newMessage = string.Empty;
        }
    }
}

Blazor.start({
    circuit: {
        reconnectionOptions: {
            retryIntervalMilliseconds: (retryNumber) => {
                // Exponential backoff: 200ms, 400ms, 800ms, max 30s
                return Math.min(200 * Math.pow(2, retryNumber), 30000);
            },
            maxRetries: 15
        }
    }
});

@page "/privacy"
@attribute [ExcludeFromInteractiveRouting]

<PageTitle>Privacy Policy</PageTitle>

<!-- This page always renders as static HTML -->
<!-- Even if global interactivity is enabled -->
<article>
    <h1>Privacy Policy</h1>
    <p>Last updated: April 2026</p>
    <!-- Content -->
</article>

# Publish with AOT for production
dotnet publish -c Release -p:RunAOTCompilation=true