安装 SignalR .NET client Nuget 包

Install-Package Microsoft.AspNetCore.SignalR.Client

连接SignalR Hub

使用 HubConnectionBuilder 类并调用 Build方法与Signal R Hub 建立连接。在建立连接的同时，可以配置请求Header，Log level，协议类型（protocol），传输类型（transport type），等其它选项。

设置好连接后使用StartAsync启动连接。

using System;
using System.Threading.Tasks;
using System.Windows;
using Microsoft.AspNetCore.SignalR.Client;

namespace SignalRChatClient
{
public partial class MainWindow : Window
{
HubConnection connection;
public MainWindow()
{
InitializeComponent();

connection = new HubConnectionBuilder()
.WithUrl("http://localhost:53353/ChatHub")
.Build();

connection.Closed += async (error) =>
{
await Task.Delay(new Random().Next(0,5) * 1000);
await connection.StartAsync();
};
}

private async void connectButton_Click(object sender, RoutedEventArgs e)
{
connection.On<string, string>("ReceiveMessage", (user, message) =>
{
this.Dispatcher.Invoke(() =>
{
var newMessage = $"{user}: {message}";
messagesList.Items.Add(newMessage);
});
});

try
{
await connection.StartAsync();
messagesList.Items.Add("Connection started");
connectButton.IsEnabled = false;
sendButton.IsEnabled = true;
}
catch (Exception ex)
{
messagesList.Items.Add(ex.Message);
}
}

private async void sendButton_Click(object sender, RoutedEventArgs e)
{
try
{
await connection.InvokeAsync("SendMessage",
userTextBox.Text, messageTextBox.Text);
}
catch (Exception ex)
{
messagesList.Items.Add(ex.Message);
}
}
}
}

连接中断异常处理

自动重新连接

连接中断后自动重新连接，可以通过配置直接完成。

HubConnection connection= new HubConnectionBuilder()
.WithUrl(new Uri(“http://127.0.0.1:5000/chatHub”))
.WithAutomaticReconnect()
.Build();

还可以在WithAutomaticReconnect()中配置等待重新连接的时间秒数。

通过自定义HubConnectionState.Reconnecting事件可以自定义处理每次重新连接时要执行的操作。

connection.Reconnecting += error =>
{
Debug.Assert(connection.State == HubConnectionState.Reconnecting);

// Notify users the connection was lost and the client is reconnecting.
// Start queuing or dropping messages.

return Task.CompletedTask;
};

类似的，还有自定义的 Connected 事件方法。

connection.Reconnected += connectionId =>
{
Debug.Assert(connection.State == HubConnectionState.Connected);

// Notify users the connection was reestablished.
// Start dequeuing messages queued while reconnecting if any.

return Task.CompletedTask;
};

WithAutomaticReconnect() 只能处理连接后的中断连接的重新连接行为，不能处理首次连接失败的情况。首次连接的失败处理需要采用以下方式。

public static async Task<bool> ConnectWithRetryAsync(HubConnection connection, CancellationToken token)
{
// Keep trying to until we can start or the token is canceled.
while (true)
{
try
{
await connection.StartAsync(token);
Debug.Assert(connection.State == HubConnectionState.Connected);
return true;
}
catch when (token.IsCancellationRequested)
{
return false;
}
catch
{
// Failed to connect, trying again in 5000 ms.
Debug.Assert(connection.State == HubConnectionState.Disconnected);
await Task.Delay(5000);
}
}
}

自动重连接，执行4次后如果仍然失败，就会触发connection.Closed += error =>的事件。

connection.Closed += error =>
{
Debug.Assert(connection.State == HubConnectionState.Disconnected);

// Notify users the connection has been closed or manually try to restart the connection.

return Task.CompletedTask;
};

重连接的等待时间也可以分别设置不同时长。

HubConnection connection= new HubConnectionBuilder()
.WithUrl(new Uri(“http://127.0.0.1:5000/chatHub”))
.WithAutomaticReconnect(new[] { TimeSpan.Zero, TimeSpan.Zero, TimeSpan.FromSeconds(10) })
.Build();

// .WithAutomaticReconnect(new[] { TimeSpan.Zero, TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(30) }) yields the default behavior.

手动重连接

手动重连接是通过connection.Closed事件的自定义处理的。可以自由的设置等待时长。

connection.Closed += async (error) =>
{
await Task.Delay(new Random().Next(0,5) * 1000);
await connection.StartAsync();
};

调用Signal R Hub 方法

await connection.InvokeAsync(“SendMessage”, userTextBox.Text, messageTextBox.Text);

从Signal R Hub 调用 client 方法

connection.On<string, string>(“ReceiveMessage”, (user, message) => { this.Dispatcher.Invoke(() => { var newMessage = $”{user}: {message}“; messagesList.Items.Add(newMessage); }); });

这个方法实际执行是通过SendMessage方法执行的。