在列表视图中删除项目时，该项目消失

Question

我正在使用Gongsolution框架来处理拖放功能。但是我有一个问题。当我取消选择某个项目并将其拖放到另一个项目时，被删除的项目就消失了。当我选择其他项目时出现一个项目。预先谢谢你。

处理拖放功能的代码：

        public static bool CanAcceptData(IDropInfo dropInfo)
        {
            if (dropInfo == null || dropInfo.DragInfo == null)
            {
                return false;
            }

            if (!dropInfo.IsSameDragDropContextAsSource)
            {
                return false;
            }

            // do not drop on itself
            var isTreeViewItem = dropInfo.InsertPosition.HasFlag(RelativeInsertPosition.TargetItemCenter)
                                 && dropInfo.VisualTargetItem is TreeViewItem;
            if (isTreeViewItem && dropInfo.VisualTargetItem == dropInfo.DragInfo.VisualSourceItem)
            {
                return false;
            }

            if (dropInfo.DragInfo.SourceCollection == dropInfo.TargetCollection)
            {
                var targetList = dropInfo.TargetCollection.TryGetList();
                return targetList != null;
            }
            //      else if (dropInfo.DragInfo.SourceCollection is ItemCollection) {
            //        return false;
            //      }
            else if (dropInfo.TargetCollection == null)
            {
                return false;
            }
            else
            {
                if (TestCompatibleTypes(dropInfo.TargetCollection, dropInfo.Data))
                {
                    var isChildOf = IsChildOf(dropInfo.VisualTargetItem, dropInfo.DragInfo.VisualSourceItem);
                    return !isChildOf;
                }
                else
                {
                    return false;
                }
            }
        }

        public static IEnumerable ExtractData(object data)
        {
            if (data is IEnumerable && !(data is string))
            {
                return (IEnumerable)data;
            }

            return Enumerable.Repeat(data, 1);
        }

        public static void SelectDroppedItems(IDropInfo dropInfo, IEnumerable items, bool applyTemplate = true, bool focusVisualTarget = true)
        {
            if (dropInfo == null) throw new ArgumentNullException(nameof(dropInfo));
            if (items == null) throw new ArgumentNullException(nameof(items));
            var itemsControl = dropInfo.VisualTarget as ItemsControl;
            if (itemsControl != null)
            {
                var tvItem = dropInfo.VisualTargetItem as TreeViewItem;
                var tvItemIsExpanded = tvItem != null && tvItem.HasHeader && tvItem.HasItems && tvItem.IsExpanded;

                var itemsParent = tvItemIsExpanded ? tvItem : (dropInfo.VisualTargetItem != null ? ItemsControl.ItemsControlFromItemContainer(dropInfo.VisualTargetItem) : itemsControl);
                itemsParent = itemsParent ?? itemsControl;

                itemsParent.ClearSelectedItems();

                foreach (var obj in items)
                {
                    if (applyTemplate)
                    {
                        // call ApplyTemplate for TabItem in TabControl to avoid this error:
                        //
                        // System.Windows.Data Error: 4 : Cannot find source for binding with reference
                        var container = itemsParent.ItemContainerGenerator.ContainerFromItem(obj) as FrameworkElement;
                        container?.ApplyTemplate();
                    }
                    itemsParent.SetItemSelected(obj, true);
                }

                if (focusVisualTarget)
                {
                    itemsControl.Focus();
                }
            }
        }

        public static bool ShouldCopyData(IDropInfo dropInfo)
        {
            // default should always the move action/effect
            if (dropInfo == null || dropInfo.DragInfo == null)
            {
                return false;
            }
            var copyData = ((dropInfo.DragInfo.DragDropCopyKeyState != default(DragDropKeyStates)) && dropInfo.KeyStates.HasFlag(dropInfo.DragInfo.DragDropCopyKeyState))
                           || dropInfo.DragInfo.DragDropCopyKeyState.HasFlag(DragDropKeyStates.LeftMouseButton);
            copyData = copyData
                       //&& (dropInfo.DragInfo.VisualSource != dropInfo.VisualTarget)
                       && !(dropInfo.DragInfo.SourceItem is HeaderedContentControl)
                       && !(dropInfo.DragInfo.SourceItem is HeaderedItemsControl)
                       && !(dropInfo.DragInfo.SourceItem is ListBoxItem);
            return copyData;
        }
        public virtual void DragOver(IDropInfo dropInfo)
        {
            if (CanAcceptData(dropInfo))
            {
                dropInfo.Effects = ShouldCopyData(dropInfo) ? DragDropEffects.Copy : DragDropEffects.Move;
                var isTreeViewItem = dropInfo.InsertPosition.HasFlag(RelativeInsertPosition.TargetItemCenter) && dropInfo.VisualTargetItem is TreeViewItem;
                dropInfo.DropTargetAdorner = isTreeViewItem ? DropTargetAdorners.Highlight : DropTargetAdorners.Insert;
            }
        }
        public virtual void Drop(IDropInfo dropInfo)
        {
            if (dropInfo == null || dropInfo.DragInfo == null)
            {
                return;
            }

            var insertIndex = dropInfo.UnfilteredInsertIndex;

            var itemsControl = dropInfo.VisualTarget as ItemsControl;
            if (itemsControl != null)
            {
                var editableItems = itemsControl.Items as IEditableCollectionView;
                if (editableItems != null)
                {
                    var newItemPlaceholderPosition = editableItems.NewItemPlaceholderPosition;
                    if (newItemPlaceholderPosition == NewItemPlaceholderPosition.AtBeginning && insertIndex == 0)
                    {
                        ++insertIndex;
                    }
                    else if (newItemPlaceholderPosition == NewItemPlaceholderPosition.AtEnd && insertIndex == itemsControl.Items.Count)
                    {
                        --insertIndex;
                    }
                }
            }

            var destinationList = dropInfo.TargetCollection.TryGetList();
            var data = ExtractData(dropInfo.Data).OfType<object>().ToList();

            var copyData = ShouldCopyData(dropInfo);
            if (!copyData)
            {
                var sourceList = dropInfo.DragInfo.SourceCollection.TryGetList();
                if (sourceList != null)
                {
                    foreach (var o in data)
                    {
                        var index = sourceList.IndexOf(o);
                        if (index != -1)
                        {
                            sourceList.RemoveAt(index);
                            // so, is the source list the destination list too ?
                            if (destinationList != null && Equals(sourceList, destinationList) && index < insertIndex)
                            {
                                --insertIndex;
                            }
                        }
                    }
                }
            }

            if (destinationList != null)
            {
                var objects2Insert = new List<object>();

                // check for cloning
                var cloneData = dropInfo.Effects.HasFlag(DragDropEffects.Copy) || dropInfo.Effects.HasFlag(DragDropEffects.Link);
                foreach (var o in data)
                {
                    var obj2Insert = o;
                    if (cloneData)
                    {
                        var cloneable = o as ICloneable;
                        if (cloneable != null)
                        {
                            obj2Insert = cloneable.Clone();
                        }
                    }

                    objects2Insert.Add(obj2Insert);
                    destinationList.Insert(insertIndex++, obj2Insert);
                }

                // Robimy drag and drop i odznaczamy zaznaczony element (nie odznaczal sie) - naprawione
                IndexesOfSelectedEmployees.Clear();
                IndexesOfSelectedEmployees.Add(--insertIndex);

                var selectDroppedItems = itemsControl is TabControl || (itemsControl != null && GongSolutions.Wpf.DragDrop.DragDrop.GetSelectDroppedItems(itemsControl));
                if (selectDroppedItems)
                {
                    SelectDroppedItems(dropInfo, objects2Insert);
                }
            }
        }

        protected static bool IsChildOf(UIElement targetItem, UIElement sourceItem)
        {
            var parent = ItemsControl.ItemsControlFromItemContainer(targetItem);

            while (parent != null)
            {
                if (parent == sourceItem)
                {
                    return true;
                }

                parent = ItemsControl.ItemsControlFromItemContainer(parent);
            }

            return false;
        }

        protected static bool TestCompatibleTypes(IEnumerable target, object data)
        {
            TypeFilter filter = (t, o) => { return (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(IEnumerable<>)); };

            var enumerableInterfaces = target.GetType().FindInterfaces(filter, null);
            var enumerableTypes = from i in enumerableInterfaces
                                  select i.GetGenericArguments().Single();

            if (enumerableTypes.Count() > 0)
            {
                var dataType = TypeUtilities.GetCommonBaseClass(ExtractData(data));
                return enumerableTypes.Any(t => t.IsAssignableFrom(dataType));
            }
            else
            {
                return target is IList;
            }
        }
        public static readonly DependencyProperty SelectDroppedItemsProperty;
        public static bool GetSelectDroppedItems(UIElement target)
        {
            return (bool)target.GetValue(SelectDroppedItemsProperty);
        }

用于选择和取消选择项目的代码：

public void ClickMethod(object parameter)
        {
            List<Employee> selection = ((IList)parameter).Cast<Employee>().ToList();

            if (Keyboard.IsKeyDown(Key.LeftCtrl))
            {
                if (SelectedEmployee == null)
                {
                    IndexesOfSelectedEmployees.Clear();
                    CountOfSelectedEmployees = 0;
                    DynamicSearchEmployeeName = String.Empty;
                    DynamicSearchEmployeeID = String.Empty;
                    DynamicSearchEmployeeSalary = String.Empty;
                    DynamicSearchEmployeeDesigner = String.Empty;
                    DynamicSearchEmployeeEmailID = String.Empty;
                }

                if (SelectedEmployee != null)
                {
                    foreach (Employee item in Employees)
                    {
                        if (item.IsSelected == true)
                        {
                            IndexesOfSelectedEmployees.Add(Employees.IndexOf(item));
                        }
                        if (item.IsSelected == false)
                        {
                            IndexesOfSelectedEmployees.Remove(Employees.IndexOf(item));
                        }
                    }

                    SelectedEmployee = Employees[IndexesOfSelectedEmployees.Last()];
                    //SelectedEmployee = selection.Last();

                    foreach (int itemIndexesOfSelectedEmployees in IndexesOfSelectedEmployees.Reverse())
                    {
                        foreach (Employee itemEmployees in Employees)
                        {
                            if (itemIndexesOfSelectedEmployees == Employees.IndexOf(itemEmployees))
                            {
                                itemEmployees.IsSelected = true;
                            }
                        }
                    }
                    CountOfSelectedEmployees = selection.Count;
                }
            }
            else if (!IndexesOfSelectedEmployees.Any())
            {
                IndexesOfSelectedEmployees.Clear();
                IndexesOfSelectedEmployees.Add(SelectedIndex.GetValueOrDefault());
                CountOfSelectedEmployees = selection.Count;
            }
            else if (IndexesOfSelectedEmployees.Any())
            {
                if (IndexesOfSelectedEmployees.Count == 1 && IndexesOfSelectedEmployees.Contains((int)SelectedIndex))
                {
                    //IndexesOfSelectedEmployees.Add(Employees.IndexOf(SelectedEmployee));
                    //SelectedEmployee.IsSelected = false;
                    SelectedEmployee = null;
                    CountOfSelectedEmployees = 0;
                    IndexesOfSelectedEmployees.Clear();
                    DynamicSearchEmployeeName = String.Empty;
                    DynamicSearchEmployeeID = String.Empty;
                    DynamicSearchEmployeeSalary = String.Empty;
                    DynamicSearchEmployeeDesigner = String.Empty;
                    DynamicSearchEmployeeEmailID = String.Empty;

                }
                else if (IndexesOfSelectedEmployees.Count == 1 && !IndexesOfSelectedEmployees.Contains((int)SelectedIndex))
                {
                    IndexesOfSelectedEmployees.Clear();
                    IndexesOfSelectedEmployees.Add(SelectedIndex.GetValueOrDefault());
                    CountOfSelectedEmployees = 1; 
                }
                else if (IndexesOfSelectedEmployees.Count != 1)
                {
                    IndexesOfSelectedEmployees.Clear();
                    IndexesOfSelectedEmployees.Add(SelectedIndex.GetValueOrDefault());
                    SelectedEmployee = Employees[IndexesOfSelectedEmployees.Last()];
                    foreach (int itemIndexesOfSelectedEmployees in IndexesOfSelectedEmployees)
                    {
                        foreach (Employee itemEmployees in Employees)
                        {
                            if (itemIndexesOfSelectedEmployees == Employees.IndexOf(itemEmployees))
                            {
                                itemEmployees.IsSelected = true;
                            }
                            if (itemIndexesOfSelectedEmployees != Employees.IndexOf(itemEmployees))
                            {
                                itemEmployees.IsSelected = false;
                            }
                        }
                    }
                    CountOfSelectedEmployees = selection.Count;
                }
            }


        }




public void OnSelectionChanged(object parameter)
        {
            IList selection = (IList)parameter;

            if ((Keyboard.IsKeyDown(Key.LeftCtrl) && (Keyboard.IsKeyDown(Key.A))) == true || (Keyboard.IsKeyDown(Key.LeftShift) && Keyboard.IsKeyDown(Key.Up)) || (Keyboard.IsKeyDown(Key.LeftShift) && Keyboard.IsKeyDown(Key.Down)))
            {
                CountOfSelectedEmployees = selection.Count;

                foreach (Employee item in selection)
                {
                    IndexesOfSelectedEmployees.Add(Employees.IndexOf(item));
                }
                foreach (int itemIndexesOfSelectedEmployees in IndexesOfSelectedEmployees)
                {
                    foreach (Employee itemEmployees in Employees)
                    {
                        if (itemIndexesOfSelectedEmployees == Employees.IndexOf(itemEmployees))
                        {
                            itemEmployees.IsSelected = true;
                        }
                    }
                }
            }
        }