Drag and Drop in Windows Forms TreeView

29 Apr 202119 minutes to read

The drag and drop functionality is fully supported through the various drag drop events.

Events Table

TreeNodeAdv Events	Description
DragDrop	Specifies the function to be triggered after an item is dropped.
DragEnter	Specifies the function to be triggered when an item is dragged inside the control bounds.
DragLeave	Specifies the function to be triggered when an item is dragged outside the control bounds.
DragOver	Specifies the function to be triggered when an item is dragged over the control bounds.
GiveFeedback	Specifies the function to trigger when the mouse drags an item. The system request the control to provide feedback to that effect.
ItemDrag	Specifies the function to be triggered when an item is dragged.
QueryContinueDrag	Specifies the function to be triggered when an item is being dragged.

The drag and drop functionality can be implemented by using the below code snippets.

C#

private void treeViewAdv_ItemDrag(object sender, System.Windows.Forms.ItemDragEventArgs e)
{
    TreeViewAdv treeViewAdv = sender as TreeViewAdv;

// The TreeViewAdv always provides an array of selected nodes.
    TreeNodeAdv[] nodes = e.Item as TreeNodeAdv[];

// Let us get only the first selected node.
    TreeNodeAdv node = nodes[0];
    DragDropEffects result = treeViewAdv.DoDragDrop(node, DragDropEffects.Move);
}

// Helps keep track of the node that is being dragged.
    private TreeNodeAdv currentSourceNode;
    private void treeViewAdv_DragOver(object sender, System.Windows.Forms.DragEventArgs e)
    {
// Determine drag effects
        bool droppable = true;
        TreeNodeAdv destinationNode = null;
        TreeViewAdv treeView = sender as TreeViewAdv;
        Point ptInTree = treeView.PointToClient(new Point(e.X, e.Y));
        this.currentSourceNode = null;

// Looking for a single tree node.
        if( e.Data.GetDataPresent(typeof(TreeNodeAdv)))
        {
// Get the destination and source node.
            destinationNode = treeView.GetNodeAtPoint(ptInTree);
            TreeNodeAdv sourceNode = (TreeNodeAdv) e.Data.GetData(typeof(TreeNodeAdv));
            this.currentSourceNode = sourceNode;
            droppable = true;
        }
        else
        droppable = false;
        if(droppable)
// If Moving is allowed:
        e.Effect = DragDropEffects.Move;
        else
        e.Effect = DragDropEffects.None;
        Point pt = this.treeViewAdv1.PointToClient(new Point(e.X, e.Y));
        this.treeViewAdv1.SelectedNode = this.treeViewAdv1.GetNodeAtPoint(pt);
        Console.WriteLine(this.treeViewAdv1.SelectedNode.Text);
    }
    private void treeViewAdv_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)  
    {
        TreeViewAdv treeView = sender as TreeViewAdv;
// Get the destination and source node.
        TreeNodeAdv sourceNode = (TreeNodeAdv) e.Data.GetData(typeof(TreeNodeAdv));
        Point pt = this.treeViewAdv1.PointToClient(new Point(e.X, e.Y));
        TreeNodeAdv destinationNode = this.treeViewAdv1.GetNodeAtPoint(pt);
        sourceNode.Move(destinationNode, NodePositions.Next);
        this.currentSourceNode = null;
        treeView.SelectedNode = sourceNode;
    }
    private void treeViewAdv_DragLeave(object sender, System.EventArgs e)
    {
// Let the highlight tracker keep track of the current highlight node.
        this.treeViewDragHighlightTracker.ClearHighlightNode();
    }
    private void treeViewAdv_QueryContinueDrag(object sender, System.Windows.Forms.QueryContinueDragEventArgs e)
    {
// Cancel dragging when Escape was pressed.
        if(e.EscapePressed)
        {
            e.Action = DragAction.Cancel;
        }
    }
    private void treeViewAdv_DragEnter(object sender, System.Windows.Forms.DragEventArgs e) 
    {
// Reset the label text.
        DropLocationLabel.Text = "None";
    }
    public event GiveFeedbackEventHandler GiveFeedback;
    private System.Windows.Forms.CheckBox UseCustomCursorsCheck;
    private Cursor MyNoDropCursor;
    private Cursor MyNormalCursor;
    private void treeViewAdv_GiveFeedback(object sender, System.Windows.Forms.GiveFeedbackEventArgs e) 
    {
// Use custom cursors if the check box is checked.
        if (UseCustomCursorsCheck.Checked) 
        {
            MyNormalCursor = new Cursor("3dwarro.cur");
            MyNoDropCursor = new Cursor("3dwno.cur");
            if (MyNormalCursor != null)
            MyNormalCursor.Dispose();
            if (MyNoDropCursor != null)
            MyNoDropCursor.Dispose();
// Sets the custom cursor based upon the effect.
           e.UseDefaultCursors = false;
           if ((e.Effect & DragDropEffects.Move) == DragDropEffects.Move)
           Cursor.Current = MyNormalCursor;
       else 
           Cursor.Current = MyNoDropCursor;
        }
    }

VB.NET

Private Sub treeViewAdv_ItemDrag(ByVal sender As Object, ByVal e As System.Windows.Forms.ItemDragEventArgs)
Dim treeViewAdv As TreeViewAdv = CType(IIf(TypeOf sender Is TreeViewAdv, sender, Nothing), TreeViewAdv)

' The TreeViewAdv always provides an array of selected nodes.
Dim nodes As TreeNodeAdv() = CType(IIf(TypeOf e.Item Is TreeNodeAdv, e.Item, Nothing), TreeNodeAdv)()

' Let us get only the first selected node.
Dim node As TreeNodeAdv = nodes(0)
Dim result As DragDropEffects = treeViewAdv.DoDragDrop(node, DragDropEffects.Move)
End Sub

' Helps keep track of the node that is being dragged.
Private currentSourceNode As TreeNodeAdv
Private Sub treeViewAdv_DragOver(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs)

' Determine drag effects
Dim droppable As Boolean = True
Dim destinationNode As TreeNodeAdv = Nothing
Dim treeView As TreeViewAdv = CType(IIf(TypeOf sender Is TreeViewAdv, sender, Nothing), TreeViewAdv)
Dim ptInTree As Point = treeView.PointToClient(New Point(e.X, e.Y))
Me.currentSourceNode = Nothing

' Looking for a single tree node.
If e.Data.GetDataPresent(GetType(TreeNodeAdv)) Then

' Get the destination and source node.
destinationNode = treeView.GetNodeAtPoint(ptInTree)
Dim sourceNode As TreeNodeAdv = CType(e.Data.GetData(GetType(TreeNodeAdv)), TreeNodeAdv)
Me.currentSourceNode = sourceNode
droppable = True
Else
droppable = False
End If
If droppable Then

' If Moving is allowed:
e.Effect = DragDropEffects.Move
Else
e.Effect = DragDropEffects.None
End If
Dim pt As Point = Me.treeViewAdv1.PointToClient(New Point(e.X, e.Y))
Me.treeViewAdv1.SelectedNode = Me.treeViewAdv1.GetNodeAtPoint(pt)
Console.WriteLine(Me.treeViewAdv1.SelectedNode.Text)
End Sub
Private Sub treeViewAdv_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs)
Dim treeView As TreeViewAdv = CType(IIf(TypeOf sender Is TreeViewAdv, sender, Nothing), TreeViewAdv)

' Get the destination and source node.
Dim sourceNode As TreeNodeAdv = CType(e.Data.GetData(GetType(TreeNodeAdv)), TreeNodeAdv)
Dim pt As Point = Me.treeViewAdv1.PointToClient(New Point(e.X, e.Y))
Dim destinationNode As TreeNodeAdv = Me.treeViewAdv1.GetNodeAtPoint(pt)
sourceNode.Move(destinationNode, NodePositions.Next)
Me.currentSourceNode = Nothing
treeView.SelectedNode = sourceNode
End Sub
Private Sub treeViewAdv_DragEnter(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragEnter

' Reset the label text.
DropLocationLabel.Text = "None"
End Sub
Private Sub treeViewAdv_DragLeave(ByVal sender As Object, ByVal e As System.EventArgs) Handles treeViewAdv1.DragLeave

' Let the highlight tracker keep track of the current highlight node.
Me.treeViewDragHighlightTracker.ClearHighlightNode()
End Sub
Private Sub treeViewAdv_QueryContinueDrag(ByVal sender As Object, ByVal e As System.Windows.Forms.QueryContinueDragEventArgs) Handles treeViewAdv1.QueryContinueDrag

' Cancel dragging when Escape was pressed.
If e.EscapePressed Then
e.Action = DragAction.Cancel
End If
End Sub
Public Event GiveFeedback As GiveFeedbackEventHandler
Friend WithEvents UseCustomCursorsCheck As System.Windows.Forms.CheckBox 
Private MyNoDropCursor As Cursor 
Private MyNormalCursor As Cursor 
Private Sub treeViewAdv_GiveFeedback(ByVal sender As Object, ByVal e As GiveFeedbackEventArgs) Handles ListDragSource.GiveFeedback

' Use custom cursors if the check box is checked.
If (UseCustomCursorsCheck.Checked) Then
MyNormalCursor = New Cursor("3dwarro.cur") 
MyNoDropCursor = New Cursor("3dwno.cur") 

' Set the custom cursor based upon the effect.
e.UseDefaultCursors = False
If ((e.Effect And DragDropEffects.Move) = DragDropEffects.Move) Then
Cursor.Current = MyNormalCursor
Else
Cursor.Current = MyNoDropCursor
End If
End If
End Sub

The below image indicates dragging of “Brazil” node.

Selection Settings While Drag Drop

While performing a drag and drop operation, when a node is selected and dragged, the node will be drawn with a dotted rectangle, when it loses focus. This feature is enabled by setting the KeepDottedSelection property of the TreeViewAdv to true.

The semi-transparent image which is drawn besides the cursor, during the drag and drop operation, can be displayed at a distance from the mouse cursor, by enabling the KeepDragCapturePoint property.

The semi-transparent image that is drawn, can be hidden or shown using the ShowDragNodeCue property.

Property Table

treeViewAdv Property	Description
KeepDottedSelection	Value which indicates if the selected node must draw a dotted rectangle when it loses focus.
KeepDragCapturePoint	Gets or sets a value which indicates whether cue image should be drawn at a distance below the cursor during the drag drop operation. Default value is false.
ShowDragNodeCue	Specifies whether a semitransparent image of the selected node is drawn besides the cursor during the drag and drop operation.

To cancel the selection or editing, use CancelMode and CancelEditMode methods.

Methods Table

treeViewAdv methods	Description
CancelMode	Cancels the selection or editing of a node.
CancelEditMode	Cancels the edit mode of a particular node.
LastMousePositionToClient	Gets the last mouse position to the client or returns the last point at which the mouse is clicked.

Row Selection

The FullRowSelect property allows you to specify if the entire row of the selected item is highlighted and clicking anywhere on an item’s row causes it to be selected.

Property Table

TreeViewAdv Property	Description
FullRowSelect	Specifies whether the whole row of a treeview needs to be selected on selecting a node of that row.

Method Table

TreeViewAdv Method	Description
GetHeightOfRows	To get the height of the rows of a tree from the start point to the end point. The parameters are,(i)start - Represents the start point. (ii)end - Represents the end point.

C#

this.treeViewAdv1.GetHeightOfRows(1, 2);

VB.NET

Me.treeViewAdv1.GetHeightOfRows(1, 2)

Highlighting Drag and Drop

Drag drop operation in the TreeView can display a highlighted line during dragging. TreeView uses a helper class, i.e., TreeViewAdvDragHighlightTracker for this purpose. This keeps track of the highlighted node and also provides the destination where the user had decided to drop. It also allows validation whether to drag / drop a node to another node or not. We need to use the tracker class for this purpose.

C#

//In the Drag Over event

// Let the highlight tracker keep track of the current highlight node.
this.treeViewDragHighlightTracker.SetHighlightNode(destinationNode, ptInTree);

//In the Drag Leave event
this.treeViewDragHighlightTracker.ClearHighlightNode();

//In the Drag Drop event
private void treeViewAdv_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
{
    TreeViewAdv treeView = sender as TreeViewAdv;
// Get the destination and source node.
    TreeNodeAdv sourceNode = (TreeNodeAdv) e.Data.GetData(typeof(TreeNodeAdv));
    TreeNodeAdv destinationNode = this.treeViewDragHighlightTracker.HighlightNode;
    TreeViewDropPositions dropPosition = this.treeViewDragHighlightTracker.DropPosition;

// Clear the highlight info in the tracker.
    this.treeViewDragHighlightTracker.ClearHighlightNode();
    if(destinationNode != null)
    {
        switch (dropPosition)
        {
            case TreeViewDropPositions.AboveNode:
            sourceNode.Move(destinationNode, NodePositions.Previous);
            break;

            case TreeViewDropPositions.BelowNode:
            sourceNode.Move(destinationNode, NodePositions.Next);
            break;

            case TreeViewDropPositions.OnNode:
            sourceNode.Move(destinationNode.Nodes);
            destinationNode.Expand();
            break;
        }
    }
    this.currentSourceNode = null;

// Move the source node based on the tracked info.
    treeView.SelectedNode = sourceNode;
}

VB.NET

'In the Drag Over event

' Let the highlight tracker keep track of the current highlight node.
Me.treeViewDragHighlightTracker.SetHighlightNode(destinationNode, ptInTree)

'In the Drag Leave event
Me.treeViewDragHighlightTracker.ClearHighlightNode()

'In the Drag Drop event
Private Sub treeViewAdv_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles treeViewAdv1.DragDrop
Dim treeView As TreeViewAdv = CType(IIf(TypeOf sender Is TreeViewAdv, sender, Nothing), TreeViewAdv)

' Get the destination and source node.
Dim sourceNode As TreeNodeAdv = CType(e.Data.GetData(GetType(TreeNodeAdv)), TreeNodeAdv)
Dim destinationNode As TreeNodeAdv = Me.treeViewDragHighlightTracker.HighlightNode
Dim dropPosition As TreeViewDropPositions = Me.treeViewDragHighlightTracker.DropPosition

' Clear the highlight info in the tracker.
Me.treeViewDragHighlightTracker.ClearHighlightNode()
Me.currentSourceNode = Nothing

' Move the source node based on the tracked info.
If Not destinationNode Is Nothing Then
Select Case dropPosition
Case TreeViewDropPositions.AboveNode
sourceNode.Move(destinationNode, NodePositions.Previous)
Case TreeViewDropPositions.BelowNode
sourceNode.Move(destinationNode, NodePositions.Next)
Case TreeViewDropPositions.OnNode
sourceNode.Move(destinationNode.Nodes)
destinationNode.Expand()
End Select
End If
treeView.SelectedNode = sourceNode
End Sub

Note: We can also prevent drawing highlight for some nodes using QueryAllowedPositionForNode event.

Painting the HighlightTracker Pen

This can be done using TreeViewAdvDragHighlightTracker.QueryDragInsertInfo event.

Property Table

TreeViewAdv Property	Description
QueryDragInsertInfo	Occurs before drawing a drag insert position.

C#

//QueryDragInsertInfo
this.treeViewDragHighlightTracker.QueryDragInsertInfo+=
new QueryDragInsertInfoEventHandler(treeViewDragHighlightTracker_QueryDragInsertInfo);

// Changing the color of the highlight tracker Pen
private void treeViewDragHighlightTracker_QueryDragInsertInfo(object sender, QueryDragInsertInfoEventArgs args)
{
    args.DragInsertColor=Color.Orange;
}

VB.NET

' QueryDragInsertInfo
AddHandler treeViewDragHighlightTracker.QueryDragInsertInfo, AddressOf treeViewDragHighlightTracker_QueryDragInsertInfo

' Changing the color of the highlight tracker Pen.
Private Sub treeViewDragHighlightTracker_QueryDragInsertInfo(ByVal sender As Object, ByVal args As QueryDragInsertInfoEventArgs)
args.DragInsertColor = Color.Orange
End Sub