小吳 VBQA 程式設計討論

以下是在Tree View下的Drag & Drop的程式，但問題是當選了一個Node之後並開始Drag時，整個Tree View Area也同時Drag。請問這是甚麼緣故？
Private Sub tvIGD_DragDrop(Source As Control, x As Single, y As Single)
'If no Node is highlighted then get out
If tvIGD.DropHighlight Is Nothing Then
bDropFlag = False
　　Exit Sub
Else
'If dropping on itself then get out
　　If xNode = tvIGD.DropHighlight Then
　　　　Text1.Text = "Cannot drop itself"
　　　　Exit Sub
　　End If
　　If Mid$(tvIGD.DropHighlight.Key, 1, 3) = "LV2" Then
　　　　'Assign an element to the group
　　　　Call sAddNode
　　End If
　　Set tvIGD.DropHighlight = Nothing
　　bDropFlag = False
End If
End Sub
Private Sub tvIGD_DragOver(Source As Control, x As Single, y As Single, State As Integer)
Dim xTempNode As Node
If bDropFlag Then
'Set DropHighLight to the mouse's coordinates only
　　'if the node is a group type
　　Set xTempNode = tvIGD.HitTest(x, y)
　　If Not xTempNode Is Nothing Then
　　　　If Mid$(xTempNode.Key, 1, 3) = "LV2" Then　 'It is a Group
　　　　　　Set tvIGD.DropHighlight = xTempNode
　　　　End If
　　End If
End If
End Sub

Private Sub tvIGD_MouseDown(Button As Integer, Shift As Integer, x As Single, y As Single)
'Set the item being dragged
Set xNode = tvIGD.SelectedItem
End Sub
Private Sub tvIGD_MouseMove(Button As Integer, Shift As Integer, x As Single, y As Single)
Dim sTempNode As Node
'Signal a Drag operation
If Button = vbLeftButton Then
'Only allow dragging if it is an element
　　Set sTempNode = tvIGD.HitTest(x, y)
　　If Not sTempNode Is Nothing Then
　　　　If Mid$(sTempNode.Key, 1, 3) = "LV1" Then　 'It is an element
　　　　　　bDropFlag = True　　'Set the flag to true
　　　　　　tvIGD.Drag vbBeginDrag　'Drag operation
　　　　End If
　　End If
End If
End Sub