Implement new managed client.

Source/MQTTnet.Extensions.ManagedClient/New/Events/ConnectingFailedEventArgs.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using MQTTnet.Client;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public sealed class ConnectingFailedEventArgs : EventArgs
+    {
+        public ConnectingFailedEventArgs(MqttClientConnectResult connectResult, Exception exception)
+        {
+            ConnectResult = connectResult;
+            Exception = exception;
+        }
+
+        /// <summary>
+        ///     This is null when the server was not reachable and thus no MQTT response was transmitted.
+        /// </summary>
+        public MqttClientConnectResult ConnectResult { get; }
+
+        public Exception Exception { get; }
+    }
+}