HOWTO: Scroll the TreeView When Dragging and Dropping a Node

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0

SUMMARY

The TreeView control supports drag-and-drop. When a Node is dragged to the top or bottom of the control, the control does not automatically scroll vertically. Because the control does not support scrolling when doing drag- and-drop, scrolling must be implemented by the developer. This article demonstrates one way to implement scrolling when performing drag-and-drop.

MORE INFORMATION

The following example uses API calls to scroll the TreeView when the mouse pointer gets close to the bottom or top of the control and you are doing a drag-and-drop of a Node.

Step-by-Step Example

1. Create a new standard EXE project.Form1 is created by default.

2. Click Components on the Project menu. Check "Microsoft Windows Common Controls 5.0."

3. Add a Treeview, ImageList, and Timer to Form1.

4. Right-click the ImageList Control and select Properties from the pop-up menu.

5. On the General Tab of the Property Pages dialog, select 16 x 16.

6. Click the Images Tab, and insert 2 ICO files. NOTE: Icon files can be found in the directory ..\VB\Graphics\Icon.

7. Add the following code to the Code Window of Form1:

         Option Explicit
   

         Private Declare Function SendMessage Lib "user32" Alias _
           "SendMessageA" (ByVal hwnd As Long, _
           ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
         Dim mfX As Single
         Dim mfY As Single
         Dim moNode As Node
         Dim m_iScrollDir As Integer 'Which way to scroll
         Dim mbFlag As Boolean
   
         Private Sub Form_DragOver(Source As Control, x As Single, y As _
           Single, State As Integer)
            If Source.Name = "TreeView1" Then
               Timer1.Enabled = False
            End If
         End Sub
   
         Private Sub Form_Load()
            Dim i As Integer
            Dim n As Integer
            Timer1.Enabled = False
            Timer1.Interval = 200
            TreeView1.Style = tvwTreelinesPlusMinusPictureText
            TreeView1.ImageList = ImageList1
            'Populate TreeView controls
            For i = 1 To 50
              TreeView1.Nodes.Add Text:="Node " & i, Image:=1, _
                 SelectedImage:=2
            Next i
            For i = 1 To 50
              For n = 1 To 5
                 TreeView1.Nodes.Add Relative:=i, Relationship:=tvwChild, _
                  Text:="Child Node " & n, _
                  Image:=1, SelectedImage:=2
              Next n
            Next i
         End Sub
   
         Private Sub Timer1_Timer()
            Set TreeView1.DropHighlight = TreeView1.HitTest(mfX, mfY)
            If m_iScrollDir = -1 Then 'Scroll Up
            ' Send a WM_VSCROLL message 0 is up and 1 is down
              SendMessage TreeView1.hwnd, 277&, 0&, vbNull
            Else 'Scroll Down
              SendMessage TreeView1.hwnd, 277&, 1&, vbNull
            End If
         End Sub
   
         Private Sub TreeView1_DragDrop(Source As Control, x As Single, _
           y As Single)
         ' If you were moving the Node you dragged to be the child
         ' of the Node you dropped it on, you would need to
         ' make moNode the selected Node after you made it a child
           If Not TreeView1.DropHighlight Is Nothing Then
             MsgBox moNode.Text & " was dropped on " & _
             TreeView1.DropHighlight.Text
           End If
           Set TreeView1.DropHighlight = Nothing
           Set moNode = Nothing
           Timer1.Enabled = False
         End Sub
   
         Private Sub TreeView1_DragOver(Source As Control, x As Single, _
         y As Single, State As Integer)
           Set TreeView1.DropHighlight = TreeView1.HitTest(x, y)
           mfX = x
           mfY = y
           If y > 0 And y < 100 Then 'scroll up
             m_iScrollDir = -1
             Timer1.Enabled = True
           ElseIf y > (TreeView1.Height - 200) And y < TreeView1.Height Then
           'scroll down
             m_iScrollDir = 1
             Timer1.Enabled = True
           Else
             Timer1.Enabled = False
           End If
         End Sub
   
         Private Sub TreeView1_MouseUp(Button As Integer, Shift As Integer, _
         x As Single, y As Single)
          Timer1.Enabled = False
         End Sub
   
         Private Sub TreeView1_MouseDown(Button As Integer, Shift As _
         Integer, x As Single, y As Single)
          TreeView1.DropHighlight = TreeView1.HitTest(x, y)
          'Make sure we are over a Node
          If Not TreeView1.DropHighlight Is Nothing Then
             TreeView1.SelectedItem = TreeView1.HitTest(x, y)
             Set moNode = TreeView1.SelectedItem ' Set the item being dragged.
          End If
          Set TreeView1.DropHighlight = Nothing
         End Sub
   
         Private Sub TreeView1_MouseMove(Button As Integer, Shift As _
         Integer, x As Single, y As Single)
          If Button = vbLeftButton Then
             TreeView1.DragIcon = TreeView1.SelectedItem.CreateDragImage
             TreeView1.Drag vbBeginDrag
          End If
         End Sub
   
   

8. Save and run the sample. Select a Node and then drag it to the bottom of the TreeView. You will see the TreeView scroll.

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q172272
   TITLE     : SAMPLE: Manipulating and Saving the Nodes in a TreeView
               Control