Fix LastSelected and LastSelectedElement properties.

zaaReloaded2/ViewModels/SettingsRepositoryViewModel.cs

@@ -33,7 +33,21 @@ namespace zaaReloaded2.ViewModels
 
         public ObservableCollection<SettingsViewModel> SettingsList { get; private set; }
 
-        public SettingsViewModel Selected { get; private set; }
+        /// <summary>
+        /// Gets the SettingsViewModel that was most recently selected. Whether
+        /// this view model is still selected can be found out be getting the
+        /// view model's IsSelected property.
+        /// </summary>
+        /// <remarks>
+        /// Due to the way the WPF ListBox (for example) is implemented, selecting
+        /// a list item will trigger an PropertyChanged event twice: Once for the
+        /// item being selected, and once for the item being deselected. Thus we
+        /// can only capture the last item that actually was selected. We cannot
+        /// howeve capture if an item was deselected without a new selection,
+        /// because we cannot logicaly connect two occurrences of the same event
+        /// from different objects.
+        /// </remarks>
+        public SettingsViewModel LastSelected { get; private set; }
 
         #endregion
 
@@ -195,23 +209,23 @@ namespace zaaReloaded2.ViewModels
         {
             if (CanEditSettings())
             {
-                EditSettingsMessage.Send(new ViewModelMessageContent(Selected));
+                EditSettingsMessage.Send(new ViewModelMessageContent(LastSelected));
             }
         }
 
         bool CanEditSettings()
         {
-            return Selected != null && !IsDefaultSettings();
+            return LastSelected != null && LastSelected.IsSelected && !IsDefaultSettings();
         }
 
         void DoUseSettings()
         {
-            UseSettingsMessage.Send(new ViewModelMessageContent(Selected));
+            UseSettingsMessage.Send(new ViewModelMessageContent(LastSelected));
         }
 
         bool CanUseSettings()
         {
-            return Selected != null;
+            return LastSelected != null && LastSelected.IsSelected;
         }
 
         void DoAddSettings()
@@ -225,7 +239,7 @@ namespace zaaReloaded2.ViewModels
 
         bool CanDeleteSettings()
         {
-            return Selected != null && !IsDefaultSettings();
+            return LastSelected != null && LastSelected.IsSelected && !IsDefaultSettings();
         }
 
         void DoDeleteSettings() 
@@ -233,7 +247,7 @@ namespace zaaReloaded2.ViewModels
             if (CanDeleteSettings())
             {
                 ConfirmDeleteSettingsMessage.Send(
-                    new ViewModelMessageContent(Selected),
+                    new ViewModelMessageContent(LastSelected),
                     param => ConfirmDeleteSettings(param));
             }
         }
@@ -265,12 +279,12 @@ namespace zaaReloaded2.ViewModels
 
         void DoCopySettings()
         {
-            if (Selected != null)
+            if (LastSelected != null)
             {
-                SettingsViewModel copy = Selected.Clone() as SettingsViewModel;
+                SettingsViewModel copy = LastSelected.Clone() as SettingsViewModel;
                 _repository.SettingsList.Add(copy.RevealModelObject() as Settings);
                 AddSettingsViewModel(copy);
-                Selected.IsSelected = false;
+                LastSelected.IsSelected = false;
                 copy.IsSelected = true;
             }
         }
@@ -280,7 +294,7 @@ namespace zaaReloaded2.ViewModels
             SettingsViewModel vm = sender as SettingsViewModel;
             if (vm != null && e.PropertyName == "IsSelected")
             {
-                Selected = vm.IsSelected ? vm : null;
+                if (vm.IsSelected) LastSelected = vm;
             }
         }
 
@@ -290,11 +304,11 @@ namespace zaaReloaded2.ViewModels
         /// </summary>
         bool IsDefaultSettings()
         {
-            if (Selected != null)
+            if (LastSelected != null)
             {
                 return
-                    (Selected.Name == zaaReloaded2.Properties.Settings.Default.SettingsNameClinic
+                    (LastSelected.Name == zaaReloaded2.Properties.Settings.Default.SettingsNameClinic
-                    || Selected.Name == zaaReloaded2.Properties.Settings.Default.SettingsNameWard);
+                    || LastSelected.Name == zaaReloaded2.Properties.Settings.Default.SettingsNameWard);
             }
             else
             {

zaaReloaded2/ViewModels/SettingsViewModel.cs

@@ -76,7 +76,16 @@ namespace zaaReloaded2.ViewModels
         /// <summary>
         /// Gets or sets the currently selected element.
         /// </summary>
-        public ElementViewModel SelectedElement
+        /// <remarks>
+        /// Due to the way the WPF ListBox (for example) is implemented, selecting
+        /// a list item will trigger an PropertyChanged event twice: Once for the
+        /// item being selected, and once for the item being deselected. Thus we
+        /// can only capture the last item that actually was selected. We cannot
+        /// howeve capture if an item was deselected without a new selection,
+        /// because we cannot logicaly connect two occurrences of the same event
+        /// from different objects.
+        /// </remarks>
+        public ElementViewModel LastSelectedElement
         {
             get { return _selectedElement; }
             set
@@ -279,7 +288,7 @@ namespace zaaReloaded2.ViewModels
                 picker.ElementChosenMessage.Sent += (sender, args) =>
                 {
                     FormatElementViewModel newVM = args.Content.ViewModel as FormatElementViewModel;
-                    AddChildElementViewModel(SelectedElement as ControlElementViewModel, newVM);
+                    AddChildElementViewModel(LastSelectedElement as ControlElementViewModel, newVM);
                 };
                 AddChildElementMessage.Send(new ViewModelMessageContent(picker));
             }
@@ -287,27 +296,30 @@ namespace zaaReloaded2.ViewModels
 
         bool CanAddChildElement()
         {
-            return SelectedElement is ControlElementViewModel;
+            return LastSelectedElement is ControlElementViewModel;
         }
 
         void DoDeleteElement() { }
 
-        bool CanDeleteElement() { return _selectedElement != null; }
+        bool CanDeleteElement() { return LastSelectedElement != null && LastSelectedElement.IsSelected; }
 
         void DoCopyElement() { }
 
-        bool CanCopyElement() { return _selectedElement != null; }
+        bool CanCopyElement() { return LastSelectedElement != null && LastSelectedElement.IsSelected; }
 
         /// <summary>
-        /// Sets or unsets the SelectedElement property whenever the IsSelected
+        /// Sets LastSelectedElement property whenever the IsSelected
-        /// property of an ElementViewModel changes.
+        /// property of an ElementViewModel changes
         /// </summary>
+        /// <remarks>
+        /// Please see the remarks on the LastSelectedElement property.
+        /// </remarks>
         void ElementViewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
         {
             ElementViewModel vm = sender as ElementViewModel;
             if (vm != null && e.PropertyName == "IsSelected")
             {
-                SelectedElement = vm.IsSelected ? vm : null;
+                if (vm.IsSelected) LastSelectedElement = vm;
             }
         }