Q177743: HOWTO: Scroll the TreeView When Dragging and Dropping a Node
Article: Q177743
Product(s): Microsoft Visual Basic for Windows
Version(s):
Operating System(s):
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
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SUMMARY
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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
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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
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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:
Q172272 : FILE: TREEVIEW: Manipulating and Saving the Nodes in a TreeView
Control
For more information on the TreeView Control, please see the Visual Basic Online
Help.
Additional query words: dragdrop dragging dropping kbVBp500 kbVBp600 kbVBp kbdsd kbDSupport kbControl
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Keywords : kbGrpDSVB
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type : kbhowto
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