Small update to Flowers sample

Samples/Flowers/Flowers.Data/ViewModel/MainViewModel.cs

@@ -61,8 +61,11 @@ namespace Flowers.Data.ViewModel
                         Flowers.Clear();
 
                         _isLoading = true;
+                        RefreshCommand.RaiseCanExecuteChanged();
                         RaisePropertyChanged(() => LastLoadedFormatted);
 
+                        Exception error = null;
+
                         try
                         {
                             var list = await _flowersService.Refresh();
@@ -76,14 +79,22 @@ namespace Flowers.Data.ViewModel
                             LastLoaded = DateTime.Now;
                         }
                         catch (Exception ex)
+                        {
+                            error = ex;
+                        }
+
+                        if (error != null)
                         {
                             var dialog = ServiceLocator.Current.GetInstance<IDialogService>();
-                            dialog.ShowError(ex, "Error when refreshing", "OK", null);
+                            await dialog.ShowError(error, "Error when refreshing", "OK", null);
                         }
 
                         _isLoading = false;
+                        RefreshCommand.RaiseCanExecuteChanged();
                         RaisePropertyChanged(() => LastLoadedFormatted);
-                    }));
+                    },
+                    
+                    () => !_isLoading));
             }
         }
 
@@ -114,12 +125,10 @@ namespace Flowers.Data.ViewModel
             _navigationService = navigationService;
             Flowers = new ObservableCollection<FlowerViewModel>();
 
-#if DEBUG
             if (IsInDesignMode)
             {
                 RefreshCommand.Execute(null);
             }
-#endif
         }
     }
 }

Samples/Flowers/Flowers.Data/ViewModel/ViewModelLocator.cs

@@ -29,8 +29,12 @@ namespace Flowers.Data.ViewModel
 
             if (ViewModelBase.IsInDesignModeStatic)
             {
+                if (!SimpleIoc.Default.IsRegistered<GalaSoft.MvvmLight.Views.INavigationService>())
+                {
+                    SimpleIoc.Default.Register<GalaSoft.MvvmLight.Views.INavigationService, DesignNavigationService>();
+                }
+
                 SimpleIoc.Default.Register<IFlowersService, DesignFlowersService>();
-                SimpleIoc.Default.Register<GalaSoft.MvvmLight.Views.INavigationService, DesignNavigationService>();
             }
             else
             {