.NET WPF Folder Picker / Folder Browser

The heart of the dialog is WPF TreeView control and underlying data model. Here is the model:

    public class TreeItem : NotifiableObject
    {
        #region Properties

        public bool IsFullyLoaded { get; set; }

        public string Name
        {
            get
            {
                return name;
            }
            set
            {
                name = value;
                NotifyPropertyChanged(() => Name);
            }
        }

        public TreeItem Parent
        {
            get
            {
                return parent;
            }
            set
            {
                parent = value;
                NotifyPropertyChanged(() => Parent);
            }
        }

        public ObservableCollection Childs
        {
            get
            {
                return childs;
            }
            set
            {
                childs = value;
                NotifyPropertyChanged(() => Childs);
            }
        }

        #endregion

        public TreeItem(string name, TreeItem parent)
        {
            Name = name;
            IsFullyLoaded = false;
            Parent = parent;
            Childs = new ObservableCollection();
        }

        public string GetFullPath()
        {
            Stack stack = new Stack();

            var ti = this;

            while (ti.Parent != null)
            {
                stack.Push(ti.Name);
                ti = ti.Parent;
            }

            string path = stack.Pop();

            while (stack.Count > 0)
            {
                path = Path.Combine(path, stack.Pop());
            }

            return path;
        }

        #region Private fields

        private string name;

        private TreeItem parent;

        private ObservableCollection childs;

        #endregion
    }

    public class DriveTreeItem : TreeItem
    {
        public DriveType DriveType { get; set; }

        public DriveTreeItem(string name, DriveType driveType, TreeItem parent)
            : base(name, parent)
        {
            DriveType = driveType;
        }
    }

And here is the control itself:

   public partial class FolderPickerControl : UserControl, INotifyPropertyChanged
    {
        #region Constants

        private static readonly string EmptyItemName = "Empty";

        #endregion

        #region Properties

        public TreeItem Root
        {
            get
            {
                return root;
            }
            private set
            {
                root = value;
                NotifyPropertyChanged(() => Root);
            }
        }

        public TreeItem SelectedItem
        {
            get
            {
                return selectedItem;
            }
            private set
            {
                selectedItem = value;
                NotifyPropertyChanged(() => SelectedItem);
            }
        }

        public string SelectedPath { get; private set; }

        #endregion

        public FolderPickerControl()
        {
            InitializeComponent();

            Init();
        }

        #region INotifyPropertyChanged Members

        public void NotifyPropertyChanged(Expression> property)
        {
            var lambda = (LambdaExpression)property;
            MemberExpression memberExpression;
            if (lambda.Body is UnaryExpression)
            {
                var unaryExpression = (UnaryExpression)lambda.Body;
                memberExpression = (MemberExpression)unaryExpression.Operand;
            }
            else memberExpression = (MemberExpression)lambda.Body;
            OnPropertyChanged(memberExpression.Member.Name);
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        #endregion

        #region Private methods

        private void Init()
        {
            root = new TreeItem("root", null);
            var systemDrives = DriveInfo.GetDrives();

            foreach (var sd in systemDrives)
            {
                var item = new DriveTreeItem(sd.Name, sd.DriveType, root);
                item.Childs.Add(new TreeItem(EmptyItemName, item));

                root.Childs.Add(item);
            }

            Root = root; // to notify UI
        }

        private void TreeView_Selected(object sender, RoutedEventArgs e)
        {
            var tvi = e.OriginalSource as TreeViewItem;
            if (tvi != null)
            {
                SelectedItem = tvi.DataContext as TreeItem;
                SelectedPath = SelectedItem.GetFullPath();
            }
        }

        private void TreeView_Expanded(object sender, RoutedEventArgs e)
        {
            var tvi = e.OriginalSource as TreeViewItem;
            var treeItem = tvi.DataContext as TreeItem;

            if (treeItem != null)
            {
                if (!treeItem.IsFullyLoaded)
                {
                    treeItem.Childs.Clear();

                    string path = treeItem.GetFullPath();

                    DirectoryInfo dir = new DirectoryInfo(path);

                    try
                    {
                        var subDirs = dir.GetDirectories();
                        foreach (var sd in subDirs)
                        {
                            TreeItem item = new TreeItem(sd.Name, treeItem);
                            item.Childs.Add(new TreeItem(EmptyItemName, item));

                            treeItem.Childs.Add(item);
                        }
                    }
                    catch { }

                    treeItem.IsFullyLoaded = true;
                }
            }
            else
                throw new Exception();
        }

        #endregion

        #region Private fields

        private TreeItem root;
        private TreeItem selectedItem;

        #endregion
    }

More code can be found here. As you can see stub childs are added for each tree item if it hasn’t been expanded yet. Lazy loading is used, so actual childs are fetched only when user expands folder or drive.

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