ASP.NET Core .NET 8 Preview 4 New Features and Updates

// Add this script tag to your Blazor Server project (wwwroot/index.html or wwwroot/_Host.cshtml)
// This script is needed to enable the new Blazor Server-Side Rendering (SSR) feature in .NET 8
// The 'suppress-error' attribute is used to ignore the specified build warning (BL9992) related to loading the script
<script src="_framework/blazor.web.js" suppress-error="BL9992"></script>

// Define page routing
@page "/fetchdata"

// Import required namespaces for the Blazor Server project
@using BlazorSSR.Data
@inject WeatherForecastService ForecastService

// Enable server-side rendering for this Blazor component using the StreamRendering attribute
@attribute [StreamRendering(true)]

<PageTitle>Weather forecast</PageTitle>

<h1>Weather forecast</h1>

// Using conditional rendering to display the "Loading..." message while data is being fetched
@if (forecasts is null)
{
    <p><em>Loading...</em></p>
}
else
{
    // Render weather forecasts when the data is available
}

@code {
    private string message;

    // Override the OnInitializedAsync method to fetch weather forecast data asynchronously
    protected override async Task OnInitializedAsync()
    {
        forecasts = await ForecastService.GetForecastAsync(DateOnly.FromDateTime(DateTime.Now));
    }
}

// Add this CascadingModelBinder component to your main layout (usually MainLayout.razor)
// The CascadingModelBinder component is used to seamlessly deal with form posts in Blazor SSR (.NET 8)
<CascadingModelBinder>
    @Body
</CascadingModelBinder>

// Define a form using the EditForm component, and ensure to set the method attribute for correct form submission handling
@inject FormDataProvider FormData

<EditForm method="POST" Model="exampleModel" OnValidSubmit="HandleSubmit">
    // Bind the Name property of the exampleModel object to the input field
    <InputText @bind-Value="exampleModel.Name" />
    // Add a submit button to trigger form submission
    <button type="submit">Submit</button>
</EditForm>

@code {
    // Instantiate an ExampleModel object
    ExampleModel exampleModel = new();

    protected override void OnInitialized()
    {
        // Manually model bind the form data using the FormDataProvider service
        if (FormData.Entries.TryGetValue("Name", out var nameValues))
        {
            exampleModel.Name = nameValues.First();
        }
    }

    void HandleSubmit()
    {
        // Handle the submitted form data
    }

    // Create a model class with the required properties (e.g., Name)
    public class ExampleModel
    {
        public string? Name { get; set; }
    }
}

// Add the WasmEnableWebcil property to your Blazor WebAssembly project file (e.g., .csproj)
// This property enables the Webcil packaging feature, which eliminates issues related to blocked .dll file downloads
<PropertyGroup>
    <WasmEnableWebcil>true</WasmEnableWebcil>
</PropertyGroup>

// Create a minimal API WebApplication instance
var app = WebApplication.Create();

// Function to generate or retrieve a file path for the uploaded file
string GetOrCreateFilePath(string fileName, string filesDirectory = "uploadFiles")
{
    var directoryPath = Path.Combine(app.Environment.ContentRootPath, filesDirectory);
    Directory.CreateDirectory(directoryPath);
    return Path.Combine(directoryPath, fileName);
}

// Function to upload the file with the specified name
async Task UploadFileWithName(IFormFile file, string fileSaveName)
{
    var filePath = GetOrCreateFilePath(fileSaveName);
    await using var fileStream = new FileStream(filePath, FileMode.Create);
    await file.CopyToAsync(fileStream);
}

// Use the MapPost method to define a POST route that accepts an IFormFile parameter without needing the FromForm attribute
app.MapPost("/upload", async (IFormFile file) => {
    var fileSaveName = Guid.NewGuid().ToString("N") + Path.GetExtension(file.FileName);
    await UploadFileWithName(file, fileSaveName);
    return TypedResults.Ok("File uploaded successfully!");
});

// Start and run the WebApplication
app.Run();

// The .http file simplifies testing your app's endpoints using the new Visual Studio HTTP editor
// Define your API host address to avoid hardcoding it in each request
@MyApi_HostAddress = http://localhost:5233

// Test a GET request to fetch all todos by using the defined API host address
GET {{MyApi_HostAddress}}/todos/
Accept: application/json

// Use the three hash (#) symbols to separate different request examples

// Test another GET request to fetch a specific todo item (e.g., with id 1)
GET {{MyApi_HostAddress}}/todos/1
Accept: application/json

// Add more request examples with different HTTP methods and endpoints as needed

// Create a minimal API WebApplication instance
var app = WebApplication.Create();

// Define an API endpoint activated by enabling the Request Delegate Generator (RDG)
// Automatic logging and exception handling are provided by RDG, simplifying development
app.MapGet("/hello/{name}", (string name)
    => $"Hello {name}!");

// Define another API endpoint that calculates age based on the input birthdate
app.MapGet("/age", (DateTime birthDate)
    => $"You're about {DateTime.Now.Year - birthDate.Year} years old!");

// Start and run the WebApplication
app.Run();

// Send a request without providing the required 'name' parameter in the /hello endpoint
// The following cURL command will cause a BadHttpRequestException, as the parameter is not specified:
curl "http://localhost:5056/hello"

// The exception message will look like this:
/*
Microsoft.AspNetCore.Http.BadHttpRequestException: Required parameter "string name" was not provided from route or query string.
   ....
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
*/

// Send a request with an unparsable 'birthDate' parameter in the /age endpoint
// The following cURL command will cause a BadHttpRequestException due to the 'invalidDate' value:
curl "http://localhost:5056/age?birthDate=invalidDate"

// The exception message will look like this:
/*
Microsoft.AspNetCore.Http.BadHttpRequestException: Failed to bind parameter "DateTime birthDate" from "invalidDate".
   ...
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
*/