TreeList.VirtualTreeGetCellValue Event

This event allows you to initialize cells (and optionally the check state) of the processed node, when populating the Tree List control with data dynamically.

Namespace: DevExpress.XtraTreeList

Assembly: DevExpress.XtraTreeList.v20.1.dll

Declaration

[DXCategory("VirtualTree")]
public event VirtualTreeGetCellValueEventHandler VirtualTreeGetCellValue
<DXCategory("VirtualTree")>
Public Event VirtualTreeGetCellValue As VirtualTreeGetCellValueEventHandler

Event Data

The VirtualTreeGetCellValue event's data class is VirtualTreeGetCellValueInfo. The following properties provide information specific to this event:

Property Description
CellData Gets or sets the current cell value (when VirtualTreeGetCellValueInfo.IsCheckState is false) or the node's check state (when VirtualTreeGetCellValueInfo.IsCheckState is true).
Column Gets the column that contains the cell currently being processed.
IsCheckState Gets whether the TreeList.VirtualTreeGetCellValue event/IVirtualTreeListData.VirtualTreeGetCellValue interface method is currently fired for you to provide a node's check state.
Node Gets an instance of the business object being currently processed.

Remarks

For more information, see Virtual Mode (Dynamic Data Loading) Using Events (Tree List Level).

Examples

The example shows how to display information on directories and files on your system in a Tree List control dynamically, using only events. The full code for this example is available in the Explorer (Virtual Tree) module of the Tree List Main Demo. Here, only a part of the code is listed, giving you a basic understanding of how the Tree List events for dynamic loading work.

To provide data for the Tree List control, the TreeList.VirtualTreeGetChildNodes and TreeList.VirtualTreeGetCellValue events are handled. The first event is used to provide lists of root and child nodes. The second event is used to provide values for node cells. To save the changes made by an end-user to node cells, the TreeList.VirtualTreeSetCellValue event is handled. However, its implementation is omitted here. In this example, it's assumed that the Tree List control contains three columns, displaying a directory/file name, a directory flag and a file size. This data is provided via the VirtualTreeGetCellValue event.

To support dynamic data loading, the TreeList.DataSource property must be set to any custom object, except an IList object or an object implementing the IVirtualTreeListData interface. In the example, the DataSource property is set to a new Object instance.

The image below shows the result.

VirtualTreeEvents

// 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) {
    //...
}
See Also