Ensuring UI thread. Making it optional.

src/net/Qml.Net.Tests/BaseTests.cs

@@ -9,6 +9,7 @@ namespace Qml.Net.Tests
 
         protected BaseTests()
         {
+            QmlNetConfig.ShouldEnsureUIThread = false; // Not need for unit tests.
             Monitor.Enter(LockObject);
         }
 

src/net/Qml.Net/Internal/DefaultCallbacks.cs

@@ -245,12 +245,12 @@ namespace Qml.Net.Internal
                 }
 
                 var result = componentCompelted.ComponentCompleted();
-                if (Tasks.ListenForExceptionsWhenInvokingTasks)
+                if (QmlNetConfig.ListenForExceptionsWhenInvokingTasks)
                 {
                     result?.ContinueWith(
                         task =>
                         {
-                            Tasks.RaiseUnhandledTaskException(task.Exception);
+                            QmlNetConfig.RaiseUnhandledTaskException(task.Exception);
                         },
                         TaskContinuationOptions.OnlyOnFaulted);
                 }
@@ -344,12 +344,12 @@ namespace Qml.Net.Internal
                 Task resultTask = null;
                 del(target, parameters, result, ref resultTask);
 
-                if (Tasks.ListenForExceptionsWhenInvokingTasks)
+                if (QmlNetConfig.ListenForExceptionsWhenInvokingTasks)
                 {
                     resultTask?.ContinueWith(
                         task =>
                         {
-                            Tasks.RaiseUnhandledTaskException(task.Exception);
+                            QmlNetConfig.RaiseUnhandledTaskException(task.Exception);
                         },
                         TaskContinuationOptions.OnlyOnFaulted);
                 }

src/net/Qml.Net/Internal/Types/NetReference.cs

@@ -25,6 +25,7 @@ namespace Qml.Net.Internal.Types
                 {
                     return obj;
                 }
+
                 throw new InvalidOperationException($"No object found for object id {ObjectId}");
             }
         }
@@ -33,6 +34,8 @@ namespace Qml.Net.Internal.Types
 
         public bool ActivateSignal(string signalName, params object[] parameters)
         {
+            QmlNetConfig.EnsureUIThread();
+
             if (parameters != null && parameters.Length > 0)
             {
                 using (var list = new NetVariantList())
@@ -45,6 +48,7 @@ namespace Qml.Net.Internal.Types
                             list.Add(variant);
                         }
                     }
+
                     return Interop.NetReference.ActivateSignal(Handle, signalName, list.Handle) == 1;
                 }
             }

src/net/Qml.Net/QCoreApplication.cs

@@ -16,7 +16,7 @@ namespace Qml.Net
         private GCHandle _triggerHandle;
         private GCHandle _aboutToQuitHandle;
         private readonly List<AboutToQuitEventHandler> _aboutToQuitEventHandlers = new List<AboutToQuitEventHandler>();
-        private static int _threadId;
+        private static int? _threadId;
 
         protected QCoreApplication(IntPtr handle, bool ownsHandle)
             : base(handle, ownsHandle)
@@ -66,7 +66,18 @@ namespace Qml.Net
             SynchronizationContext.SetSynchronizationContext(new QtSynchronizationContext(this));
         }
 
-        public static bool IsMainThread => Environment.CurrentManagedThreadId == _threadId;
+        public static bool IsMainThread
+        {
+            get
+            {
+                if (!_threadId.HasValue)
+                {
+                    throw new Exception("QCoreApplication hasn't been created yet, can't determine what thread is the main thread.");
+                }
+
+                return Environment.CurrentManagedThreadId == _threadId;
+            }
+        }
 
         public int Exec()
         {

src/net/Qml.Net/QmlNetConfig.cs

@@ -0,0 +1,38 @@
+using System;
+
+namespace Qml.Net
+{
+    public class QmlNetConfig
+    {
+        public static bool ListenForExceptionsWhenInvokingTasks { get; set; }
+
+        public static event Action<AggregateException> UnhandledTaskException;
+
+        internal static void RaiseUnhandledTaskException(AggregateException ex)
+        {
+            var handler = UnhandledTaskException;
+            handler?.Invoke(ex);
+        }
+
+        public static bool ShouldEnsureUIThread { get; set; } = true;
+
+        public static Action EnsureUIThreadDelegate = () =>
+        {
+            if (QCoreApplication.IsMainThread)
+            {
+                throw new Exception(
+                    "You must be on the UI thread to perform this task. See https://github.com/qmlnet/qmlnet/issues/112");
+            }
+        };
+
+        internal static void EnsureUIThread()
+        {
+            if (!ShouldEnsureUIThread)
+            {
+                return;
+            }
+
+            EnsureUIThreadDelegate?.Invoke();
+        }
+    }
+}

src/net/Qml.Net/Signals.cs

@@ -13,11 +13,6 @@ namespace Qml.Net
     {
         public static bool ActivateSignal(this object instance, string signalName, params object[] args)
         {
-            if (!QCoreApplication.IsMainThread)
-            {
-                throw new Exception("An attempt was made to activate a signal from a non-UI thread.");
-            }
-
             var existing = NetReference.CreateForObject(instance, false /*Ignore if not tagged*/);
             if (existing != null && existing.ActivateSignal(signalName, args))
             {

src/net/Qml.Net/Tasks.cs

@@ -1,17 +0,0 @@
-using System;
-
-namespace Qml.Net
-{
-    public static class Tasks
-    {
-        public static bool ListenForExceptionsWhenInvokingTasks { get; set; }
-
-        public static event Action<AggregateException> UnhandledTaskException;
-
-        internal static void RaiseUnhandledTaskException(AggregateException ex)
-        {
-            var handler = UnhandledTaskException;
-            handler?.Invoke(ex);
-        }
-    }
-}