When you implement drag and drop in a treeview control, you need to support some type of auto-scroll functionality. For example, when you drag an item from a visible tree node, and the destination tree node is outside of the current view of the treeview, the control should automatically scroll up or down depending on the direction of the mouse.
The Windows Forms Treeview control does not include built-in functionality to accomplish this. However, it is fairly easy to implement this yourself.
Make sure your treeview drag and drop code works correctly without autoscrolling. See the topics in this folder for more information on how to implement drag and drop in a treeview.
In order to tell the treeview to scroll up or down, you need to call the Windows API SendMessage() function. To do this, add the following code the top of your class:
// Make sure you have the correct using clause to see DllImport:
// using System.Runtime.InteropServices;
private static extern int SendMessage (IntPtr hWnd, int wMsg, int wParam,
Private Declare Function SendMessage _
Lib "user32" _
Alias "SendMessageA" _
(ByVal hwnd As IntPtr, _
ByVal wMsg As Integer, _
ByVal wParam As Integer, _
ByVal lParam As Integer) _
In the DragScroll event, determine where the mouse cursor is in relation to the top and bottom of the treeview control. Then call SendMessage to scroll as apporpriate.
' Implement an "autoscroll" routine for drag
' and drop. If the drag cursor moves to the bottom
' or top of the treeview, call the Windows API
' SendMessage function to scroll up or down automatically.
Private Sub DragScroll( _
ByVal sender As Object, _
ByVal e As DragEventArgs) _
' Set a constant to define the autoscroll region
Const ScrollRegion As Single = 20
' See where the cursor is
Dim pt As Point = TreeView1.PointToClient(Cursor.Position)
' See if we need to scroll up or down
If (pt.Y + ScrollRegion) > TreeView1.Height Then
' Call the API to scroll down
SendMessage(TreeView1.Handle, 277&, 1&, vbNull)
ElseIf (pt.Y) < TreeView1.Top + ScrollRegion Then
' Call thje API to scroll up
SendMessage(TreeView1.Handle, 277&, 0&, vbNull)
// Implement an "autoscroll" routine for drag
// and drop. If the drag cursor moves to the bottom
// or top of the treeview, call the Windows API
// SendMessage function to scroll up or down automatically.
private void DragScroll (
// Set a constant to define the autoscroll region
const Single scrollRegion = 20;
// See where the cursor is
Point pt = TreeView1.PointToClient(Cursor.Position);
// See if we need to scroll up or down
if ((pt.Y + scrollRegion) > TreeView1.Height)
// Call the API to scroll down
SendMessage(TreeView1.Handle, (int)277, (int)1, 0);
else if (pt.Y < (TreeView1.Top + scrollRegion))
// Call thje API to scroll up
SendMessage(TreeView1.Handle, (int)277, (int)0, 0);
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