SignalR教程8-服务器端Hub类的生命周期事件

一般的用于处理连接的生命周期事件是用于跟踪一个用户是否连接，或者用于保持跟踪用户名和连接ID之间的关系，处理生命周期事件可以通过重载 OnConnected, OnDisconnected, 和OnReconnected加方法入自己的代码，例子如下：

public class ContosoChatHub : Hub
{
   public override Task OnConnected()
  {
       // Add your own code here.
       // For example: in a chat application, record the association between
       // the current connection ID and user name, and mark the user as online.
       // After the code in this method completes, the client is informed that
       // the connection is established; for example, in a JavaScript client,
       // the start().done callback is executed.
       return base.OnConnected();
   }
 
   public override Task OnDisconnected()
   {
       // Add your own code here.
       // For example: in a chat application, mark the user as offline,
       // delete the association between the current connection id and user name.
       return base.OnDisconnected();
   }
 
   public override Task OnReconnected()
   {
       // Add your own code here.
       // For example: in a chat application, you might have marked the
       // user as offline after a period of inactivity; in that case
       // mark the user as online again.
       return base.OnReconnected();
   }
}

何时 OnConnected, OnDisconnected, 和OnReconnected 会被调用？

浏览器跳转新页,接着需要建立一个新的连接, 意味着SignalR 将会执行OnDisconnected方法，接着执行OnConnected 方法. 当一个新的连接建立，SignalR 总是产生一个新的连接ID（connection ID）.

OnReconnected 方法将会在短暂的失联后自动恢复时调用, 例如网络电缆中断短暂失联，在超期时间内重连。

OnDisconnected 方法将会调用，当客户端连接断开并且不能自动重连的时候，例如,当浏览器跳转到新页面. 因此, 一个可能的事件序列是OnConnected, OnReconnected, OnDisconnected; 或者OnConnected, OnDisconnected. 不会发生序列如下： OnConnected, OnDisconnected, OnReconnected .

OnDisconnected 方法在某些场景不会被调用，例如服务器宕机或者app域循环， 当另一个服务器上线或者app域完成了循环，一些客户端可能能够执行重连同时调用OnReconnected 事件.

更多信息, 参见Understanding and Handling Connection Lifetime Events in SignalR..