UWP Dispatcher should use the internal core dispatcher for state

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue2482.cs

@@ -80,13 +80,13 @@ protected override void Init()
 			var threadpoolButton = new Button { Text = "Update Instructions from Thread Pool" };
 			layout.Children.Add(threadpoolButton);
 
-			this.Dispatcher.BeginInvokeOnMainThread(() => { instructions.Text = "updated from thread pool 1"; });
+			this.Dispatcher.BeginInvokeOnMainThread(() => { instructions.Text = "updated from thread pool 1 IsInvokeRequired=" + this.Dispatcher.IsInvokeRequired; });
 
 			threadpoolButton.Clicked += (o, a) =>
 			{
 				Task.Run(() =>
 				{
-					this.Dispatcher.BeginInvokeOnMainThread(() => { instructions.Text = "updated from thread pool 2"; });
+					this.Dispatcher.BeginInvokeOnMainThread(() => { instructions.Text = "updated from thread pool 2 IsInvokeRequired=" + this.Dispatcher.IsInvokeRequired; });
 				});
 			};
 

Xamarin.Forms.Platform.UAP/Dispatcher.cs

@@ -25,6 +25,6 @@ public Dispatcher(CoreDispatcher coreDispatcher)
 			_coreDispatcher = coreDispatcher;
 		}
 
-		bool IDispatcher.IsInvokeRequired => Device.IsInvokeRequired;
+		bool IDispatcher.IsInvokeRequired => !_coreDispatcher.HasThreadAccess;
 	}
 }

Xamarin.Forms.Platform.UAP/DispatcherProvider.cs

@@ -27,6 +27,11 @@ public IDispatcher GetDispatcher(object context)
 						s_current = new Dispatcher(renderer.ContainerElement.Dispatcher);
 						return s_current;
 					}
+					else
+					{
+						s_current = new Dispatcher();
+						return s_current;
+					}
 				}
 
 				return null;