断开连接后尝试连接到 SignalR 服务器时应用程序崩溃

Question

我正在构建一个 Xamarin Android 应用程序，它使用 SignalR 进行实时聊天。当我断开连接后尝试再次连接到服务器时，应用程序崩溃，当应用程序重新启动时，它连接正常。 我有一个单例类，在我的解决方案中用于相同的引用。单例类有如下方法连接服务器：

public async Task<string> StartConnection()
    {
        hubConnection.Headers.Add("User-Agent", "mobile");
        hubConnection.Headers.Add("username", loggedUser);
        try
        {
            await hubConnection.Start();
            return "Connected..";
        }
        catch (Exception e)
        {
            return e.Message;
        }

    }

以下方法断开连接：

public void StopConnection()
    {
        hubConnection.Stop();

    }

连接在应用的MainActivity中启动，如下图所示：

      Task.Factory.StartNew(async () =>
        {
            await SignalRClientHelper.StartConnection();
            SignalRClientHelper.InvokeGetPendingConversations(loggedonuser.UserName);

        });

用户退出时连接断开，如下图：

SignalRClientHelper.StopConnection();

客户端第一次可以连接到signalR服务器没有任何问题，但是当他们注销并再次登录应用程序时，应用程序在尝试第二次服务器时崩溃。 这是错误日志：

    ava.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
    ... 2 more
Caused by: md52ce486a14f4bcd95899665e9d932190b.JavaProxyThrowable: System.InvalidOperationException: Data cannot be sent because the connection is in the disconnected state. Call start before sending any data.
  at Microsoft.AspNet.SignalR.Client.Connection.Send (System.String data) [0x0001e] in <filename unknown>:0 
  at Microsoft.AspNet.SignalR.Client.Hubs.HubProxy.Invoke[TResult,TProgress] (System.String method, System.Action`1 onProgress, System.Object[] args) [0x000e1] in <filename unknown>:0 
  at Microsoft.AspNet.SignalR.Client.Hubs.HubProxy.Invoke[T] (System.String method, System.Object[] args) [0x00000] in <filename unknown>:0 
  at Microsoft.AspNet.SignalR.Client.Hubs.HubProxy.Invoke (System.String method, System.Object[] args) [0x00000] in <filename unknown>:0 
  at Yourtime.SignalRClientHelper+<InvokeSendMessage>d__11.MoveNext () [0x0000d] in <filename unknown>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <filename unknown>:0 
  at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>m__0 (System.Object state) [0x00000] in <filename unknown>:0 
  at Android.App.SyncContext+<Post>c__AnonStorey0.<>m__0 () [0x00000] in <filename unknown>:0 
  at Java.Lang.Thread+RunnableImplementor.Run () [0x0000b] in <filename unknown>:0 
  at Java.Lang.IRunnableInvoker.n_Run (IntPtr jnienv, IntPtr native__this) [0x00009] in <filename unknown>:0 
  at (wrapper dynamic-method) System.Object:44f67f43-349f-4a1b-8234-1604bc812b68 (intptr,intptr)
    at mono.java.lang.RunnableImplementor.n_run(Native Method)
    at mono.java.lang.RunnableImplementor.run(RunnableImplementor.java:29)
    at android.os.Handler.handleCallback(Handler.java:605)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4511)

有人知道这里可能出了什么问题吗？

Answer 1

SignalR 断开连接有点错误 IMO，但您的错误清楚地表明您正在尝试在断开连接状态下调用某些东西。

我建议你改变你连接/断开的方式如下：

断开连接

var connectionToDispose = _connection; // _connection is the current connection
_connection = null;
_proxy = null;

// connection disposing can block the UI thread for about 20 seconds
// this doesn´t always happen but just in case we run it on a new thread
Task.Run(() =>
{
    try
    {
        connectionToDispose.Dispose();
    }
    catch (Exception ex)
    {
        _tracer?.WriteLine($"[{_className}] Connection could not be disposed: {ex.Message}");
    }
});

连接

if (_connection != null)
{
    return false;
}

// always create a new Hub
_connection = new HubConnection(_endpointUri);
// TODO add headers
// TODO create proxy again and subscribe to server events (proxy.On...), etc

try
{
    _tracer?.WriteLine($"[{_className}] CONNECTING...");
    await _connection.Start();

    return true;
}
catch (Exception ex)
{
    _tracer?.WriteLine($"[{_className}] CONNECTION START ERROR: {ex.Message}");
    return false;
}

仅供参考，看看这个class。我在一个应用程序中使用过多次连接/断开连接没有问题。您可以从中获得一些想法。