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Tip of the Day
Language: Visual Basic
Expertise: Advanced
Nov 5, 1999

Load Tree Subnodes on Demand

Here's a quick way to drop a drive's folder hierarchy into a TreeView control. The advantage to using this method is that folders are enumerated only when a node is expanded, so your app won't waste time adding folders the user will never look at. A dummy item is added to each folder to get a plus sign on the node, but the item is removed when the node is expanded or simply disappears if the folder has no subdirectories. This code assumes your TreeView is named tvFiles and you have a button named cmdEnum on the form. The TreeView is connected to an ImageList whose first image is a folder icon:
 
Private Type WIN32_FIND_DATA
	dwFileAttributes As Long
	ftCreationTime As Currency 'FILETIME
	ftLastAccessTime As Currency 'FILETIME
	ftLastWriteTime As Currency 'FILETIME
	nFileSizeHigh As Long
	nFileSizeLow As Long
	dwReserved0 As Long
	dwReserved1 As Long
	cFileName As String * 260
	cAlternate As String * 14
End Type
Private Const FILE_ATTRIBUTE_DIRECTORY = &H10

Private Declare Function FindFirstFile Lib _
	"kernel32" Alias "FindFirstFileA" _
	(ByVal lpFileName As String, lpFindFileData _
	As WIN32_FIND_DATA) As Long
Private Declare Function FindNextFile Lib _
	"kernel32" Alias "FindNextFileA" _
	(ByVal hFindFile As Long, lpFindFileData _
	As WIN32_FIND_DATA) As Long
Private Declare Function FindClose Lib _
	"kernel32" (ByVal hFindFile As Long) As Long

Private Sub EnumFilesUnder(n As Node)
	Dim hFind As Long
	Dim sPath As String, oldPath As String
	Dim wf As WIN32_FIND_DATA
	Dim n2 As Node
	sPath = n.FullPath & "\*.*"
	hFind = FindFirstFile(sPath, wf)
	Do
		' Get the filename, if any.
		If InStr(wf.cFileName, vbNullChar) > 0 Then
			sPath = Left$(wf.cFileName, _
				InStr(wf.cFileName, vbNullChar) - 1)
		Else
			sPath = wf.cFileName
		End If
		If Len(sPath) = 0 Or StrComp(sPath, _
			oldPath) = 0 Then
			' Nothing found?
			Exit Do
		ElseIf sPath <> "." And sPath <> ".." Then
			' Add file with folder image
			If (wf.dwFileAttributes And _
				FILE_ATTRIBUTE_DIRECTORY) _
				= FILE_ATTRIBUTE_DIRECTORY Then
				Set n2 = tvFiles.Nodes.Add(n, _
					tvwChild, , wf.cFileName, 1, 1)
				' Add a dummy item so the + sign is 
				' displayed
				tvFiles.Nodes.Add n2, tvwChild
				n2.Sorted = True
			End If
		End If
		FindNextFile hFind, wf
		oldPath = sPath
	Loop
	FindClose hFind
End Sub

Private Sub cmdEnum_Click()
	tvFiles.Nodes.Clear
	' Add an "initializing" item
	tvFiles.Nodes.Add , , , "C:", 1
	tvFiles.Nodes(1).Sorted = True
	EnumFilesUnder tvFiles.Nodes.Item(1)
	' Make sure the root is expanded
	tvFiles.Nodes(1).Expanded = True
End Sub

Private Sub tvFiles_Expand(ByVal Node _
	As ComctlLib.Node)
	If Node.Children = 1 Then
		' Remove the "dummy" item
		tvFiles.Nodes.Remove Node.Child.Index
		' Enumerate file system items under 
		' this node
		EnumFilesUnder Node
	End If
End Sub
Ben Baird
 
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