Implement DeleteElementCommand.

Tests/ViewModels/SettingsViewModelTest.cs

@@ -106,7 +106,25 @@ namespace Tests.ViewModels
         [Test]
         public void DeleteElement()
         {
-            throw new NotImplementedException();
+            Settings settings = new Settings();
+            settings.AddElement(new SelectFirstDay());
+            settings.AddElement(new SelectEachDay());
+            settings.AddElement(new SelectLastDay());
+            SettingsViewModel settingsVM = new SettingsViewModel(settings);
+            int oldCount = settingsVM.Elements.Count;
+            ElementViewModel elementVM = settingsVM.Elements.First();
+            ElementBase element = elementVM.RevealModelObject() as ElementBase;
+            Assert.IsTrue(settings.Elements.Contains(element),
+                "Settings object does not contain the model that the VM revealed?!");
+            elementVM.IsSelected = true;
+            Assert.IsTrue(settingsVM.DeleteElementCommand.CanExecute(null),
+                "DeleteElementCommand should be enabled.");
+            settingsVM.DeleteElementCommand.Execute(null);
+            Assert.AreEqual(oldCount - 1, settingsVM.Elements.Count);
+            Assert.IsFalse(settingsVM.Elements.Contains(elementVM),
+                "Elements collection still contains the deleted element view model.");
+            Assert.IsFalse(settings.Elements.Contains(element),
+                "Settings' Element collection still contains the element model.");
         }
 
         [Test]

zaaReloaded2/ViewModels/ControlElementViewModel.cs

@@ -62,10 +62,24 @@ namespace zaaReloaded2.ViewModels
         public void AddChildElement(FormatElementViewModel viewModel)
         {
             Elements.Add(viewModel);
+            viewModel.Parent = this;
             ControlElementBase e = Element as ControlElementBase;
             e.FormatElements.Add(viewModel.RevealModelObject() as FormatElementBase);
         }
 
+        public void RemoveChildElement(FormatElementViewModel viewModel)
+        {
+            if (!Elements.Contains(viewModel))
+            {
+                throw new InvalidOperationException(
+                    "Cannot remove child view model that is not in the collection.");
+            }
+            Elements.Remove(viewModel);
+            ((ControlElementBase)Element).FormatElements
+                .Remove(viewModel.RevealModelObject() as FormatElementBase);
+            viewModel.Parent = null;
+        }
+
         #endregion
     }
 }

zaaReloaded2/ViewModels/FormatElementViewModel.cs

@@ -39,6 +39,12 @@ namespace zaaReloaded2.ViewModels
             }
         }
 
+        /// <summary>
+        /// Gets or sets the parent ControlElementViewModel, if
+        /// there is any.
+        /// </summary>
+        public ControlElementViewModel Parent { get; set; }
+
         #endregion
 
         #region Constructors

zaaReloaded2/ViewModels/SettingsViewModel.cs

@@ -299,7 +299,38 @@ namespace zaaReloaded2.ViewModels
             return LastSelectedElement is ControlElementViewModel;
         }
 
-        void DoDeleteElement() { }
+        /// <summary>
+        /// Deletes the selected element.
+        /// </summary>
+        /// <remarks>
+        /// The following algorithm ist used to find out whether the selected
+        /// element is at the first or the second level of the hierarchy:
+        /// If the Element is a ControlElement, it must be at the first level.
+        /// If the Element is a FormatElement, its Parent property will be
+        /// Null if the Element is at the first level.
+        /// </remarks>
+        void DoDeleteElement()
+        {
+            if (CanDeleteElement())
+            {
+                if (LastSelectedElement is ControlElementViewModel ||
+                    ((FormatElementViewModel)LastSelectedElement).Parent == null)
+                {
+                    // First level of the hierarchy
+                    Elements.Remove(LastSelectedElement);
+                    ElementBase element = LastSelectedElement.RevealModelObject() as ElementBase;
+                    _settings.Elements.Remove(element);
+                }
+                else
+                {
+                    // Second level of the hierarchy
+                    FormatElementViewModel formatVM = LastSelectedElement as FormatElementViewModel;
+                    ControlElementViewModel parent = formatVM.Parent;
+                    parent.RemoveChildElement(formatVM);
+                }
+                LastSelectedElement = null;
+            }
+        }
 
         bool CanDeleteElement() { return LastSelectedElement != null && LastSelectedElement.IsSelected; }