SignalR Core-从WebAPI检查连接状态

Question

我正在使用Microsoft.AspNetCore.SignalR.Client从WebAPI项目打开的连接来连接和调用SignalR Hub项目中的方法。这些是托管在单独服务器上的单独项目。

如何检查连接是否已启动，所以我不会尝试两次启动？

我使用以下代码从WebAPI连接：

public class ChatApi
{
    private readonly HubConnection _connection;

    public ChatApi()
    {
        var connection = new HubConnectionBuilder();
        _connection = connection.WithUrl("https://localhost:44302/chathub").Build();
    }

    public async Task SendMessage(Msg Model)
    {
        await _connection.StartAsync();
        await _connection.SendAsync("Send", model);
    }
}

由于我的WebAPI将大量调用SignalR，因此我想在WebAPI和SignalR之间创建单个连接，而不是每次都关闭/打开该连接。此刻，我将ChatApi类创建为单例，并在构造函数中初始化集线器连接。

在致电之前，我如何检查连接是否已启动await _connection.StartAsync();？

使用：Microsoft.AspNetCore.SignalR.Clientv1.0.0-preview1-final

Answer 1

没有ConnectionState财产。

您需要通过订阅上的Closed事件来自己跟踪状态HubConnection。

public class ChatApi
{
    private readonly HubConnection _connection;

    private ConnectionState _connectionState = ConnectionState.Disconnected;

    public ChatApi()
    {
        var connection = new HubConnectionBuilder();
        _connection = connection.WithUrl("https://localhost:44302/chathub").Build();

        // Subscribe to event
        _connection.Closed += (ex) =>
        {
            if (ex == null)
            {
                Trace.WriteLine("Connection terminated");
                _connectionState = ConnectionState.Disconnected;
            }
            else
            {
                Trace.WriteLine($"Connection terminated with error: {ex.GetType()}: {ex.Message}");
                _connectionState = ConnectionState.Faulted;
            }
        };
    }

    public async Task StartIfNeededAsync()
    {
        if (_connectionState == ConnectionState.Connected)
        {
            return;
        }

        try
        {
            await _connection.StartAsync();
            _connectionState = ConnectionState.Connected;
        }
        catch (Exception ex)
        {
            Trace.WriteLine($"Connection.Start Failed: {ex.GetType()}: {ex.Message}");
            _connectionState = ConnectionState.Faulted;
            throw;
        }
    }

    private enum ConnectionState
    {
        Connected,
        Disconnected,
        Faulted
    }
}

用法：

public async Task SendMessage(Msg model)
{
    await StartIfNeededAsync();
    await _connection.SendAsync("Send", model);
}

参考：SignalR / benchmarkapps / Crankier / Client.cs