本示例展示了如何只使用事件，在 TreeList 控件中动态显示系统中目录和文件的信息。 此示例的完整代码在 XtraTreeList Main Demo 中的 Explorer (Virtual Tree) 模块中可用。 此处只列出了一部分代码，给出 TreeList 事件如何动态加载工作的基础理解。

为了为 TreeList 控件提供数据，接管了 TreeList.VirtualTreeGetChildNodes 和 TreeList.VirtualTreeGetCellValue 事件。 第一个事件用于提供根节点和子节点的列表。 第二个事件用于提供节点单元格的取值。 为了保存由最终用户对节点单元格作出的更改，接管了 TreeList.VirtualTreeSetCellValue 事件。 但是，在此处省略了它的实现。 在本例中，假设 TreeList 控件包含三个列，显示目录/文件名称、目录标记和文件大小。 通过 VirtualTreeGetCellValue 事件来提供数据。

为了支持动态数据加载，TreeList.DataSource 属性必须被设置为任何自定义对象，但除去 IList 对象或实现了 IVirtualTreeListData interface 接口的对象之外。 在本示例中，DataSource 属性值被设置为一个新的 Object 实例。

下面的插图展示了运行结果。

C#CopyCode image复制代码
// 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) {
    //...
}
Visual BasicCopyCode image复制代码
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