TreeList.VirtualTreeGetCellValue Event

// Specifies whether the root nodes that represent the local drivers are created. 
bool loadDrives = false;
private void Form1_Load(object sender, System.EventArgs e) {
    treeList1.DataSource = new object();
}

// Indicates whether the processed node corresponds to the file. 
bool IsFile(DirectoryInfo info){
    return (info.Attributes & FileAttributes.Directory) == 0;
}

// Initializes cell values. 
private void treeList1_VirtualTreeGetCellValue(object sender, 
DevExpress.XtraTreeList.VirtualTreeGetCellValueInfo e) {
    DirectoryInfo di = new DirectoryInfo((string)e.Node);
    if (e.Column == treeListColumn1) 
            e.CellData = di.Name;
    if (e.Column == treeListColumn2) {
        if (!IsFile(di))
            e.CellData = "Folder";
        else 
            e.CellData = "File";
    }
    if (e.Column == treeListColumn3) {
        if (IsFile(di)){
            e.CellData = new FileInfo((string)e.Node).Length;
        }
        else e.CellData = null;
    }
}

// Creates and initializes child nodes. 
private void treeList1_VirtualTreeGetChildNodes(object sender, 
DevExpress.XtraTreeList.VirtualTreeGetChildNodesInfo e) {
    if (!loadDrives){ // create drives 
        string[] root = Directory.GetLogicalDrives();
        e.Children = root;
        loadDrives = true;
    }
    else {
        try{
            string path  = (string)e.Node;
            if(Directory.Exists(path)){
                string[] dirs = Directory.GetDirectories(path);
                string[] files = Directory.GetFiles(path);
                string[] arr = new string[dirs.Length + files.Length];
                dirs.CopyTo(arr,0);
                files.CopyTo(arr,dirs.Length);
                e.Children = arr;
            }
            else e.Children = new object[]{};
        }
        catch { e.Children = new object[]{}; }
    }
}

private void treeList1_VirtualTreeSetCellValue(object sender, VirtualTreeSetCellValueInfo e) {
    //... 
}

Dim loadDrives As Boolean = False 
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
    TreeList1.DataSource = New Object()
End Sub 

Function IsFile(ByVal info As DirectoryInfo) As Boolean 
    Return (info.Attributes And FileAttributes.Directory) = 0
End Function 

Private Sub TreeList1_VirtualTreeGetCellValue(ByVal sender As Object, _
ByVal e As DevExpress.XtraTreeList.VirtualTreeGetCellValueInfo) _
Handles TreeList1.VirtualTreeGetCellValue
    Dim di As New DirectoryInfo(CStr(e.Node))
    If e.Column Is TreeListColumn1 Then 
        e.CellData = di.Name
    End If 
    If e.Column Is TreeListColumn2 Then 
        If Not IsFile(di) Then 
            e.CellData = "Folder" 
        Else 
            e.CellData = "File" 
        End If 
    End If 
    If e.Column Is TreeListColumn3 Then 
        If IsFile(di) Then 
            e.CellData = New FileInfo(CStr(e.Node)).Length
        Else 
            e.CellData = Nothing 
        End If 
    End If 
End Sub 

Private Sub TreeList1_VirtualTreeGetChildNodes(ByVal sender As Object, _
ByVal e As DevExpress.XtraTreeList.VirtualTreeGetChildNodesInfo) _
Handles TreeList1.VirtualTreeGetChildNodes
    If loadDrives = False Then 
        Dim root As String() = Directory.GetLogicalDrives()
        e.Children = root
        loadDrives = True 
    Else 
        Try 
            Dim path As String = CStr(e.Node)
            If Directory.Exists(path) Then 
                Dim dirs As String() = Directory.GetDirectories(path)
                Dim files As String() = Directory.GetFiles(path)
                Dim arr(dirs.Length + files.Length) As String 
                dirs.CopyTo(arr, 0)
                files.CopyTo(arr, dirs.Length)
                e.Children = arr
            Else 
                e.Children = New Object() {}
            End If 
        Catch 
        End Try 
    End If 
End Sub 

Private Sub TreeList1_VirtualTreeSetCellValue(ByVal sender As System.Object, _
ByVal e As DevExpress.XtraTreeList.VirtualTreeSetCellValueInfo) _
Handles TreeList1.VirtualTreeSetCellValue
    '... 
End Sub