C# and WPF tutorial files

WPF/03-TreeViewsSimpleViewModel/WpfTreeView/Directory/ViewModels/DirectoryItemViewModel.cs

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+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Windows.Input;
+
+namespace WpfTreeView
+{
+    /// <summary>
+    /// A view model for each directory item
+    /// </summary>
+    public class DirectoryItemViewModel : BaseViewModel
+    {
+        #region Public Properties
+
+        /// <summary>
+        /// The type of this item
+        /// </summary>
+        public DirectoryItemType Type { get; set; }
+
+        /// <summary>
+        /// The full path to the item
+        /// </summary>
+        public string FullPath { get; set; }
+
+        /// <summary>
+        /// The name of this directory item
+        /// </summary>
+        public string Name { get { return this.Type == DirectoryItemType.Drive ? this.FullPath : DirectoryStructure.GetFileFolderName(this.FullPath); } }
+
+        /// <summary>
+        /// A list of all children contained inside this item
+        /// </summary>
+        public ObservableCollection<DirectoryItemViewModel> Children { get; set; }
+
+        /// <summary>
+        /// Indicates if this item can be expanded
+        /// </summary>
+        public bool CanExpand { get { return this.Type != DirectoryItemType.File; } }
+
+        /// <summary>
+        /// Indicates if the current item is expanded or not
+        /// </summary>
+        public bool IsExpanded
+        {
+            get
+            {
+                return this.Children?.Count(f => f != null) > 0;
+            }
+            set
+            {
+                // If the UI tells us to expand...
+                if (value == true)
+                    // Find all children
+                    Expand();
+                // If the UI tells us to close
+                else
+                    this.ClearChildren();
+            }
+        }
+
+        #endregion
+
+        #region Public Commands
+
+        /// <summary>
+        /// The command to expand this item
+        /// </summary>
+        public ICommand ExpandCommand { get; set; }
+
+        #endregion
+
+        #region Constructor
+
+        /// <summary>
+        /// Default constructor
+        /// </summary>
+        /// <param name="fullPath">The full path of this item</param>
+        /// <param name="type">The type of item</param>
+        public DirectoryItemViewModel(string fullPath, DirectoryItemType type)
+        {
+            // Create commands
+            this.ExpandCommand = new RelayCommand(Expand);
+
+            // Set path and type
+            this.FullPath = fullPath;
+            this.Type = type;
+
+            // Setup the children as needed
+            this.ClearChildren();
+        }
+
+        #endregion
+
+        #region Helper Methods
+
+        /// <summary>
+        /// Removes all children from the list, adding a dummy item to show the expand icon if required
+        /// </summary>
+        private void ClearChildren()
+        {
+            // Clear items
+            this.Children = new ObservableCollection<DirectoryItemViewModel>();
+
+            // Show the expand arrow if we are not a file
+            if (this.Type != DirectoryItemType.File)
+                this.Children.Add(null);
+        }
+
+        #endregion
+
+        /// <summary>
+        ///  Expands this directory and finds all children
+        /// </summary>
+        private void Expand()
+        {
+            // We cannot expand a file
+            if (this.Type == DirectoryItemType.File)
+                return;
+
+            // Find all children
+            var children = DirectoryStructure.GetDirectoryContents(this.FullPath);
+            this.Children = new ObservableCollection<DirectoryItemViewModel>(
+                                children.Select(content => new DirectoryItemViewModel(content.FullPath, content.Type)));
+        }
+    }
+}