Scenario: Populate RadTreeView with data coming from an XML: https://docs.telerik.com/devtools/winforms/treeview/data-binding/binding-to-xml-data The XML file stores a boolean value "IsActive" which will determine the check state of the node. Then, specify the RadTreeView. CheckMember property as well

            string fileName = @"TempFile.xml";
            DataSet tocDataSet = new DataSet("Toc");
            tocDataSet.ReadXml(fileName);
            this.radTreeView1.DataMember = "FlatNode";
            this.radTreeView1.DisplayMember = "Title";
            this.radTreeView1.ChildMember = "Id";
            this.radTreeView1.ParentMember = "ParentId";
            this.radTreeView1.CheckedMember = "IsActive";
            this.radTreeView1.DataSource = tocDataSet;

When you try to check/uncheck a node, an exception occurs indicating the inability to convert the string value "On" to ToggleState. Currently RadTreeView supports only bool, bool? to ToggleState and vice versa. The TypeConverter should be exposed so the developer can change it and implement the custom conversion.

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfFlatNode xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <FlatNode>
    <Title>New Name</Title>
    <IsActive>false</IsActive>
    <ParentId>0</ParentId>
    <Id>1</Id>
  </FlatNode>
  <FlatNode>
    <Title>1st Node</Title>
    <IsActive>false</IsActive>
    <ParentId>1</ParentId>
    <Id>2</Id>
  </FlatNode>
  <FlatNode>
    <Title>1.1</Title>
    <IsActive>true</IsActive>
    <ParentId>2</ParentId>
    <Id>3</Id>
  </FlatNode>
  <FlatNode>
    <Title>1.2</Title>
    <IsActive>false</IsActive>
    <ParentId>2</ParentId>
    <Id>4</Id>
  </FlatNode>
  <FlatNode>
    <Title>1.3</Title>
    <IsActive>false</IsActive>
    <ParentId>2</ParentId>
    <Id>5</Id>
  </FlatNode>
  <FlatNode>
    <Title>2.0</Title>
    <IsActive>true</IsActive>
    <ParentId>1</ParentId>
    <Id>6</Id>
  </FlatNode>
  <FlatNode>
    <Title>2.1</Title>
    <IsActive>true</IsActive>
    <ParentId>6</ParentId>
    <Id>7</Id>
  </FlatNode>
  <FlatNode>
    <Title>2.2</Title>
    <IsActive>true</IsActive>
    <ParentId>6</ParentId>
    <Id>8</Id>
  </FlatNode>
  <FlatNode>
    <Title>2.3</Title>
    <IsActive>true</IsActive>
    <ParentId>6</ParentId>
    <Id>9</Id>
  </FlatNode>
  <FlatNode>
    <Title>3.0</Title>
    <IsActive>true</IsActive>
    <ParentId>1</ParentId>
    <Id>10</Id>
  </FlatNode>
  <FlatNode>
    <Title>4.0</Title>
    <IsActive>false</IsActive>
    <ParentId>1</ParentId>
    <Id>11</Id>
  </FlatNode>
  <FlatNode>
    <Title>5.0</Title>
    <IsActive>true</IsActive>
    <ParentId>1</ParentId>
    <Id>12</Id>
  </FlatNode>
  <FlatNode>
    <Title>3.1</Title>
    <IsActive>false</IsActive>
    <ParentId>10</ParentId>
    <Id>13</Id>
  </FlatNode>
  <FlatNode>
    <Title>New Item</Title>
    <IsActive>true</IsActive>
    <ParentId>8</ParentId>
    <Id>15</Id>
  </FlatNode>
  <FlatNode>
    <Title>New Item</Title>
    <IsActive>true</IsActive>
    <ParentId>8</ParentId>
    <Id>16</Id>
  </FlatNode>
</ArrayOfFlatNode>

Workaround:

        class CustomTreeView : RadTreeView
        {
            //Replace the default element with the custom one
            protected override RadTreeViewElement CreateTreeViewElement()
            {
                return new CustomTreeViewElement();
            }

            //Enable theming for the control
            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadTreeView).FullName;
                }
            }
        }

        class CustomTreeViewElement : RadTreeViewElement
        {
            //Enable themeing for the element
            protected override Type ThemeEffectiveType
            {
                get
                {
                    return typeof(RadTreeViewElement);
                }
            }

            protected override bool ProcessContextMenu(Point location)
            {
                RadTreeNode node = this.GetNodeAt(location);
                if (node == null)
                {
                    RadContextMenu menu = new RadContextMenu();
                    RadMenuItem item = new RadMenuItem();
                    item.Text = "Add a root node";
                    menu.Items.Add(item);
                    item.Click += item_Click;
                    TreeViewContextMenuOpeningEventArgs args = new TreeViewContextMenuOpeningEventArgs(node, menu);
                    OnContextMenuOpening(args);

                    if (!args.Cancel)
                    {
                        menu.Show(this.ElementTree.Control, location);
                        return true;
                    }
                }
                return base.ProcessContextMenu(location);
            }

            private void item_Click(object sender, EventArgs e)
            {
                this.Nodes.Add(new RadTreeNode("New root"));
            }
        }

Say you have a button which clears the old nodes and adds a number of new child nodes to the currently selected node. If the selected node is collapsed, the newly added nodes are not visible but the scrollbar updates as if they were.

Workaround the issue by using the BeginUpdate/EndUpdate methods of RadTreeView when updating the nodes:
radTreeView1.BeginUpdate();
    node.Nodes.Clear();
    foreach (RadTreeNode treeNode in nodes)
    {
        node.Nodes.Add((RadTreeNode)treeNode.Clone());
    }
    radTreeView1.EndUpdate();

How to reproduce:
public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    private BindingList<TreeViewDataObject> data;
    public static int Id = 0;

    public RadForm1()
    {
        InitializeComponent();

        var theme = new FluentTheme();
        ThemeResolutionService.ApplicationThemeName = theme.ThemeName;

        this.data = new BindingList<TreeViewDataObject>();


        for (int i = 1; i <= 5; i += 1)
        {
            Id++;
            TreeViewDataObject root = new TreeViewDataObject()
            {
                Id = Id,
                ParentId = -1,
                Name = "Root: " + i
            };

            this.data.Add(root);

            for (int j = 1; j <= 3; j++)
            {
                Id++;
                TreeViewDataObject child = new TreeViewDataObject()
                {
                    Id = Id,
                    ParentId = root.Id,
                    Name = "Child: " + Id
                };

                this.data.Add(child);

                for (int K = 1; K <= 5; K++)
                {
                    Id++;

                    TreeViewDataObject c = new TreeViewDataObject()
                    {
                        Id = Id,
                        ParentId = child.Id,
                        Name = "Child: " + Id
                    };

                    this.data.Add(c);
                }
            }
        }

        this.radTreeView1.DataSource = this.data;
        this.radTreeView1.DisplayMember = "Name";
        this.radTreeView1.ParentMember = "ParentId";
        this.radTreeView1.ChildMember = "Id";
        this.radTreeView1.RelationBindings.Add(new RelationBinding(this.data, "Name", "ParentId", "Id"));

        this.radTreeView1.ExpandAll();

        this.radTreeView1.TreeViewElement.AllowEdit = true;
        this.radTreeView1.TreeViewElement.AllowAdd = true;
        this.radTreeView1.TreeViewElement.AllowRemove = true;
    }
}

  public class TreeViewDataObject
    {
        public int Id { get; set; }

        public int ParentId { get; set; }

        public string Name { get; set; }
    }

Workaround: Handle the ContextMenuOpening event and add logic for creating a new record in the data source object
public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    private BindingList<TreeViewDataObject> data;
    private int id = 0;

    public RadForm1()
    {
        InitializeComponent();

        var theme = new FluentTheme();
        ThemeResolutionService.ApplicationThemeName = theme.ThemeName;

        this.data = new BindingList<TreeViewDataObject>();


        for (int i = 1; i <= 5; i += 1)
        {
            id++;
            TreeViewDataObject root = new TreeViewDataObject()
            {
                Id = id,
                ParentId = -1,
                Name = "Root: " + i
            };

            this.data.Add(root);

            for (int j = 1; j <= 3; j++)
            {
                id++;
                TreeViewDataObject child = new TreeViewDataObject()
                {
                    Id = id,
                    ParentId = root.Id,
                    Name = "Child: " + id
                };

                this.data.Add(child);

                for (int K = 1; K <= 5; K++)
                {
                    id++;

                    TreeViewDataObject c = new TreeViewDataObject()
                    {
                        Id = id,
                        ParentId = child.Id,
                        Name = "Child: " + id
                    };

                    this.data.Add(c);
                }
            }
        }

        this.radTreeView1.DataSource = this.data;
        this.radTreeView1.DisplayMember = "Name";
        this.radTreeView1.ParentMember = "ParentId";
        this.radTreeView1.ChildMember = "id";
        this.radTreeView1.RelationBindings.Add(new RelationBinding(this.data, "Name", "ParentId", "id"));

        this.radTreeView1.ExpandAll();
        
        this.radTreeView1.ContextMenuOpening += RadTreeView1_ContextMenuOpening;

        this.radTreeView1.TreeViewElement.AllowEdit = true;
        this.radTreeView1.TreeViewElement.AllowAdd = true;
        this.radTreeView1.TreeViewElement.AllowRemove = true;
    }

    private void RadTreeView1_ContextMenuOpening(object sender, TreeViewContextMenuOpeningEventArgs e)
    {
        TreeViewDefaultContextMenu treeMenu = e.Menu as TreeViewDefaultContextMenu;
        treeMenu.Items.Remove(treeMenu.AddMenuItem);

        RadMenuItem item = new RadMenuItem("&New");

        item.Click -= Item_Click;
        item.Click += Item_Click;
        treeMenu.Items.Insert(2, item);
    }

    private void Item_Click(object sender, EventArgs e)
    {
        RadTreeNode parent = this.radTreeView1.SelectedNode;
        if (parent == null || parent.DataBoundItem == null)
        {
            return;
        }

        this.id++;
        BindingList<TreeViewDataObject> data = this.radTreeView1.DataSource as BindingList<TreeViewDataObject>;
        TreeViewDataObject newObject = new TreeViewDataObject()
        {
            Id = this.id,
            ParentId = ((TreeViewDataObject)parent.DataBoundItem).Id,
            Name = "New Name"
        };

        parent.Expanded = true;
        data.Add(newObject);
    }
}

public class TreeViewDataObject
{
    public int Id { get; set; }

    public int ParentId { get; set; }

    public string Name { get; set; }
}

For the MS TreeView the HideSelection property gets or sets a value indicating whether the selected tree node remains highlighted even when the tree view has lost the focus. However, it doesn't work in RadTreeView.

To reproduce: add some nodes to the tree view at design time

        public RadForm1()
        {
            InitializeComponent();

            this.radTreeView1.AllowDragDrop = true;
            this.radTreeView1.DragEnding += radTreeView1_DragEnding;
        }
        
        private void radTreeView1_DragEnding(object sender, Telerik.WinControls.UI.RadTreeViewDragCancelEventArgs e)
        {
            if (MessageBox.Show("Are you sure you want to move?", "Question", MessageBoxButtons.YesNo) == System.Windows.Forms.DialogResult.No)
            {
                e.Cancel = true;
            }
        }

Then try to drag and drop a node. You will notice that the application hangs

Workaround: use RadMessageBox

To reproduce: add several nodes at design time in order to obtain a vertical scrollbar. Enable the drag and drop functionality by setting the AllowDragDrop property to true. If you start dragging you will notice that the RadTreeView doesn't auto-scroll  when you drag close to the borders of the visible area. 

Workaround: 

    Class CustomDragDropService
        Inherits TreeViewDragDropService

        Public Sub New(ByVal owner As RadTreeViewElement)
            MyBase.New(owner)
        End Sub

        Protected Overrides Sub SetHintWindowPosition(ByVal mousePt As Point)
        End Sub
    End Class

    Class CustomTreeViewElement
        Inherits RadTreeViewElement

        Protected Overrides ReadOnly Property ThemeEffectiveType As Type
            Get
                Return GetType(RadTreeViewElement)
            End Get
        End Property

        Protected Overrides Function CreateDragDropService() As TreeViewDragDropService
            Return New CustomDragDropService(Me)
        End Function
    End Class

    Class CustomTreeView
        Inherits RadTreeView

        Protected Overrides Function CreateTreeViewElement() As RadTreeViewElement
            Return New CustomTreeViewElement()
        End Function

        Public Overrides Property ThemeClassName As String
            Get
                Return GetType(RadTreeView).FullName
            End Get
            Set(value As String)
                MyBase.ThemeClassName = value
            End Set
        End Property
    End Class

To reproduce: please refer to the attached project.

Workaround: if you access the RadTreeNode.TreeViewElement property, the TreeView property is loaded.

Workaround: call the ExpandAll method of the tree removing any nodes

When you start dragging a node you will notice that the drag hint is constantly flickering.

To reproduce:

DataTable dt = new DataTable();
 
public Form1()
{
    InitializeComponent();

    dt.Columns.Add("Id", typeof(int));
    dt.Columns.Add("ParentID", typeof(int));
    dt.Columns.Add("NodeName", typeof(string));
    dt.Rows.Add(1, 0, "Category1");
    dt.Rows.Add(2, 1, "Category2");
    dt.Rows.Add(3, 0, "Category3");
    dt.Rows.Add(4, 3, "Category4");
    dt.Rows.Add(5, 3, "Category5");
    dt.Rows.Add(6, 3, "Category6");
    dt.Rows.Add(7, 6, "Category7");
    dt.Rows.Add(8, 6, "Category8"); 

    this.radTreeView1.DataSource = dt; 

    this.radTreeView1.DisplayMember = "NodeName";
    this.radTreeView1.ChildMember = "ID";
    this.radTreeView1.ParentMember = "ParentID";

    this.radTreeView1.ExpandAll();

    this.radTreeView1.AllowAdd = true;
    this.radTreeView1.AllowRemove = true;
    this.radTreeView1.AllowDefaultContextMenu = true;

    this.radLabel1.Text = "Number of rows: " + dt.Rows.Count;
    
    this.radTreeView1.NodeRemoved += radTreeView1_NodeRemoved;
}

private void radTreeView1_NodeRemoved(object sender, Telerik.WinControls.UI.RadTreeViewEventArgs e)
{
    this.radLabel1.Text = "Number of rows: " + dt.Rows.Count;
}

Workaround: perform the delete operation programmatically by modifying the default context menu:

 this.radTreeView1.ContextMenuOpening += radTreeView1_ContextMenuOpening;

private void radTreeView1_ContextMenuOpening(object sender, TreeViewContextMenuOpeningEventArgs e)
{
    foreach (RadMenuItem item in e.Menu.Items)
    {
        if (item.Text == "&Delete")
        {
            item.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
        }
        else
        {
            item.Visibility = Telerik.WinControls.ElementVisibility.Visible;
        }
    }

    RadMenuItem removeItem = new RadMenuItem("Remove");
    e.Menu.Items.Add(removeItem);
    removeItem.Click += item_Click;
}

private void item_Click(object sender, EventArgs e)
{
    DeleteSubNodes(this.radTreeView1.SelectedNode);
    this.radLabel1.Text = "Number of rows: " + dt.Rows.Count;
}

private void DeleteSubNodes(Telerik.WinControls.UI.RadTreeNode node)
{
    if (node.Nodes.Count == 0)
    {
        dt.Rows.Remove(((DataRowView)node.DataBoundItem).Row);
    }
    else
    {
        foreach (RadTreeNode n in node.Nodes)
        {
            DeleteSubNodes(n);
        }
        dt.Rows.Remove(((DataRowView)node.DataBoundItem).Row);
    }
}

To reproduce: - add a RadTreeView - enable multiselect - select at least 1 node - call radTreeView1.SelectedNodes.Clear() Workaround: Clear the nodes manually: foreach (var node in this.radTreeView1.SelectedNodes.ToList()) { node.Selected = false; }

How to reproduce: check the attached project

Workaround: create a custom TreeViewDragDropService
class CustomTreeViewElement : RadTreeViewElement
{
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadTreeViewElement);
        }
    }

    protected override TreeViewDragDropService CreateDragDropService()
    {
        return new CustomDragDropService(this);
    }
}

class CustomTreeView : RadTreeView
{
    protected override RadTreeViewElement CreateTreeViewElement()
    {
        return new CustomTreeViewElement();
    }
 
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadTreeView).FullName;
        }
    }
}

class CustomDragDropService : TreeViewDragDropService
{
    public CustomDragDropService(RadTreeViewElement owner) 
        : base(owner)
    { }

    protected override bool CancelPreviewDragDrop(RadDropEventArgs e)
    {
        return false;
    }
}

To reproduce:

public RadForm1()
{
    InitializeComponent(); 

    for (int i = 0; i < 10; i++)
    {
        this.radTreeView1.Nodes.Add("Node1." + i); 
    }
    this.radTreeView1.AllowDragDrop = true; 
    
    this.radTreeView1.TreeViewElement.DragDropService.PreviewDragDrop+=DragDropService_PreviewDragDrop;
}

private void DragDropService_PreviewDragDrop(object sender, RadDropEventArgs e)
{
    e.Handled = true;
}

To reproduce:
for (int i = 0; i < 10; i++)
{
   this.radTreeView1.Nodes.Add("Node1." + i);
}
this.radTreeView1.AllowDragDrop = true; 

this.radTreeView1.TreeViewElement.DragDropService.ShowDragHint = false;


Workaround: this.radTreeView1.TreeViewElement.DragDropService.PreviewDragHint += DragDropService_PreviewDragHint;

private void DragDropService_PreviewDragHint(object sender, PreviewDragHintEventArgs e)
{ 
    e.UseDefaultHint = false;
}

To reproduce: please refer to the attached gif file.

Workaround: insteda of hiding the expander by the ShowExpandCollapse property use the NodeFormatting event as follows:

private void radTreeView1_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
        {
            e.NodeElement.ExpanderElement.Visibility = ElementVisibility.Collapsed;
        }

To reproduce:

radTreeView1.Filter = "new";
var node = new RadTreeNode( "test" );
radTreeView1.Nodes.Add( node );
//here the node is not in the Nodes collection
if ( radTreeView1.Nodes.Contains( node ) == false )
{
 radTreeView1.Nodes.Add( new RadTreeNode( "test" ) );
}

Workaround: remove the filter, perform the desired check and restore the filter

Scenario: We have an object P which has two lists of child objects of types C1 and C2.
If we create a list of P and we try to bind the tree to this list and display the two lists as child nodes, we will not succeed.