当使用Blazor Server时，应保证连接状态是“Connected”，才能发送数据。以下是一个示例，它演示了如何在Hub连接状态为“Connected”时发送消息：

在Blazor Server端C#代码中：

using Microsoft.AspNetCore.SignalR;

public class ChatHub : Hub
{
    public async Task SendMessage(string user, string message)
    {
        if (Context.ConnectionAborted.IsCancellationRequested)
        {
            return;
        }

        if (Context.ConnectionState == HubConnectionState.Connected)
        {
            await Clients.All.SendAsync("ReceiveMessage", user, message);
        }
        else
        {
            Console.WriteLine("Cannot send message. Connection state is {0}.", Context.ConnectionState.ToString());
        }

    }
}

在Blazor客户端C#代码中：

@inject NavigationManager NavigationManager
@inject HubConnectionProvider HubConnectionProvider


    Send Message


@code {

    private HubConnection hubConnection;

    protected override async Task OnInitializedAsync()
    {
        hubConnection = await HubConnectionProvider.GetHubConnection();
        await hubConnection.StartAsync();
    }

    public async Task SendMessage()
    {
        var message = "Hello, World!";
        try
        {
            await hubConnection.SendAsync("SendMessage", "User1", message);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
}

当连接未处于“Connected”状态时，我们在服务器端将不会发送任何消息，并在控制台上记下错误信息。因此，我们可以在上面的代码中添加自己的错误处理逻辑。