要在Blazor WebAssembly应用程序中显示文件上传进度，可以使用HttpClient的进度事件来跟踪上传进度。以下是一个示例：

1. 在Blazor组件中，添加一个文件上传输入和一个提交按钮：

上传文件

2. 在Blazor组件的代码部分，添加以下代码：

@code {
    private ElementReference fileInput;

    private async Task UploadFile()
    {
        var file = await fileInput.GetFileInfo();
        var content = new MultipartFormDataContent();

        content.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
        {
            Name = "file",
            FileName = file.Name
        };

        var progressContent = new ProgressableStreamContent(file.OpenReadStream(), (int)file.Size);
        progressContent.ProgressChanged += (s, e) =>
        {
            // 处理进度更新事件
            var progress = (double)e.BytesRead / e.TotalBytes;
            Console.WriteLine($"上传进度：{progress:P}");
        };

        content.Add(progressContent);

        var httpClient = new HttpClient();
        var response = await httpClient.PostAsync("https://example.com/upload", content);

        // 处理上传完成后的响应
        if (response.IsSuccessStatusCode)
        {
            Console.WriteLine("文件上传成功！");
        }
        else
        {
            Console.WriteLine("文件上传失败！");
        }
    }
}

3. 创建一个进度可跟踪的HttpContent类，可在上传过程中触发进度更新事件：

public class ProgressableStreamContent : StreamContent
{
    private const int DefaultBufferSize = 4096;

    public event EventHandler ProgressChanged;

    public ProgressableStreamContent(Stream content, int bufferSize = DefaultBufferSize)
        : base(content, bufferSize)
    {
    }

    protected override async Task SerializeToStreamAsync(Stream stream, TransportContext context)
    {
        var buffer = new byte[DefaultBufferSize];
        var size = await Content.ReadAsync(buffer, 0, buffer.Length);
        var uploadedBytes = 0;

        while (size > 0)
        {
            await stream.WriteAsync(buffer, 0, size);
            uploadedBytes += size;
            OnProgressChanged(uploadedBytes);

            size = await Content.ReadAsync(buffer, 0, buffer.Length);
        }
    }

    private void OnProgressChanged(int uploadedBytes)
    {
        ProgressChanged?.Invoke(this, new ProgressChangedEventArgs(uploadedBytes, Content.Length));
    }
}

public class ProgressChangedEventArgs : EventArgs
{
    public int BytesRead { get; }
    public int TotalBytes { get; }

    public ProgressChangedEventArgs(int bytesRead, int totalBytes)
    {
        BytesRead = bytesRead;
        TotalBytes = totalBytes;
    }
}

通过这种方式，你可以在Blazor WebAssembly应用程序中实现文件上传进度的显示。