Fix broken ClientWasConnected detection.

Build/MQTTnet.nuspec

@@ -12,16 +12,7 @@
     <requireLicenseAcceptance>true</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker) and supports v3.1.0, v3.1.1 and v5.0.0 of the MQTT protocol.</description>
     <releaseNotes>
-* [LowLevelClient] Fixed a null reference exception when connecting to a not existing server (thanks to @SGStino).      
-* [RcpClient] Adjusted some namespaces (BREAKING CHANGE!).
-* [AspNetCore] Adjusted some namespaces (BREAKING CHANGE!).
-* [Server] Adjusted some namespaces (BREAKING CHANGE!).
-* [Server] Added state checks (throw if not started etc.) for most server APIs.
-* [Server] Exposed real X509Certificate2 (instead byte array) to TLS options (thanks to @borigas).
-* [Server] Fixed memory leak with TCP sockets (MqttServer is now Disposable!) (BREAKING CHANGE!).
-* [Core] Fixed a null reference exception in the MqttTcpChannel with WriteAsync and ReadAsync.
-* [Core] Added server interceptor for undelivered messages (thanks to @cshark-inator).
-* [nuget] Added support for SourceLink (thanks to @JTOne123).
+* [Client] Fixed wrong value for "ClientWasConnected" in "MqttClientDisconnectedEventArgs" #976 (thanks to @dbeinder).
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2020</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin Blazor</tags> 

Source/MQTTnet/Client/MqttClient.cs

@@ -254,8 +254,7 @@ namespace MQTTnet.Client
 
             _adapter?.Dispose();
         }
-
-
+        
         protected override void Dispose(bool disposing)
         {
             if (disposing)
@@ -302,7 +301,7 @@ namespace MQTTnet.Client
 
         async Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientAuthenticateResult authenticateResult)
         {
-            var clientWasConnected = IsConnected;
+            var clientWasConnected = _isConnected;
             var reasonCode = MqttClientDisconnectReason.NormalDisconnection;
 
             TryInitiateDisconnect();

Tests/MQTTnet.Core.Tests/MqttClient_Tests.cs

@@ -23,6 +23,38 @@ namespace MQTTnet.Tests
     {
         public TestContext TestContext { get; set; }
 
+        [TestMethod]
+        public async Task Set_ClientWasConnected_On_ServerDisconnect()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                var server = await testEnvironment.StartServerAsync();
+                var client = await testEnvironment.ConnectClientAsync();
+
+                Assert.IsTrue(client.IsConnected);
+                client.UseDisconnectedHandler(e => Assert.IsTrue(e.ClientWasConnected));
+
+                await server.StopAsync();
+                await Task.Delay(4000);
+            }
+        }
+
+        [TestMethod]
+        public async Task Set_ClientWasConnected_On_ClientDisconnect()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                var server = await testEnvironment.StartServerAsync();
+                var client = await testEnvironment.ConnectClientAsync();
+
+                Assert.IsTrue(client.IsConnected);
+                client.UseDisconnectedHandler(e => Assert.IsTrue(e.ClientWasConnected));
+
+                await client.DisconnectAsync();
+                await Task.Delay(200);
+            }
+        }
+
         [TestMethod]
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Connect_To_Invalid_Server_Wrong_IP()