[DXCategory("Events")]
public event GanttTimelineCustomItemTextEventHandler CustomTimelineItemText

<DXCategory("Events")>
Public Event CustomTimelineItemText As GanttTimelineCustomItemTextEventHandler

public Form1() {
    InitializeComponent();
    // Bind the Gantt control to a data source.
    ganttControl1.DataSource = TaskData.InitData();
    // Configures the Gantt control's mappings.
    ganttControl1.TreeListMappings.KeyFieldName = "Id";
    ganttControl1.TreeListMappings.ParentFieldName = "ParentId";
    ganttControl1.ChartMappings.StartDateFieldName = "StartDate";
    ganttControl1.ChartMappings.FinishDateFieldName = "EndDate";
    ganttControl1.ChartMappings.TimelineCaption = "Name";
    // Maps the Gantt control to a field in a data source with Boolean values that
    // specify which tasks to display on the timeline when the application starts.
    ganttControl1.ChartMappings.VisibleInTimelineFieldName = "ShowInTimeline";
    // Displays the timeline at the top of the Gantt control.
    ganttControl1.OptionsTimeline.TimelinePosition = DevExpress.XtraGantt.TimelinePosition.Top;
    ganttControl1.CustomTimelineItemText += GanttControl1_CustomTimelineItemText;
}
private void GanttControl1_CustomTimelineItemText(object sender, DevExpress.XtraGantt.CustomItemTextEventArgs e) {
    // Displays a common caption if no task caption is specified.
    e.Caption = string.IsNullOrEmpty(e.Caption) ? "Noname Task" : string.Format("Task: {0}", e.Caption);
    // Displays a value from the Description data field in the task details (if specified).
    string customDetails = (string)e.Node["Description"];
    e.Details = !string.IsNullOrEmpty(customDetails) ? customDetails : e.Details;
}
public class TaskData {
    public TaskData(int id) {
        this.id = id;
    }
    int id;
    public int Id {
        get { return id; }
    }
    public bool ShowInTimeline { get; set; } = false;
    public int ParentId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public static List<TaskData> InitData() {
        return new List<TaskData>() {
            new TaskData(0){ Name = "Task A", ParentId = 0, StartDate = new DateTime(2023, 3, 1), EndDate = new DateTime(2024, 3, 31) },
            new TaskData(1){
                Name = "Task B",
                ParentId = 0,
                StartDate = new DateTime(2023, 3, 1),
                EndDate = new DateTime(2023, 7, 1),
                ShowInTimeline = true,
                Description = "The description of Task B." },
            new TaskData(2){ ParentId = 0, StartDate = new DateTime(2023, 7, 1), EndDate = new DateTime(2023, 11, 1) }
        };
    }
}

Public Sub New()
    InitializeComponent()
    ' Bind the Gantt control to a data source.
    ganttControl1.DataSource = TaskData.InitData()
    ' Configures the Gantt control's mappings.
    ganttControl1.TreeListMappings.KeyFieldName = "Id"
    ganttControl1.TreeListMappings.ParentFieldName = "ParentId"
    ganttControl1.ChartMappings.StartDateFieldName = "StartDate"
    ganttControl1.ChartMappings.FinishDateFieldName = "EndDate"
    ganttControl1.ChartMappings.TimelineCaption = "Name"
    ' Maps the Gantt control to a field in a data source with Boolean values that
    ' specify which tasks to display on the timeline when the application starts.
    ganttControl1.ChartMappings.VisibleInTimelineFieldName = "ShowInTimeline"
    ' Displays the timeline at the top of the Gantt control.
    ganttControl1.OptionsTimeline.TimelinePosition = DevExpress.XtraGantt.TimelinePosition.Top
    AddHandler ganttControl1.CustomTimelineItemText, AddressOf GanttControl1_CustomTimelineItemText
End Sub
Private Sub GanttControl1_CustomTimelineItemText(ByVal sender As Object, ByVal e As DevExpress.XtraGantt.CustomItemTextEventArgs)
    ' Displays a common caption if no task caption is specified.
    e.Caption = If(String.IsNullOrEmpty(e.Caption), "Noname Task", String.Format("Task: {0}", e.Caption))
    ' Displays a value from the Description data field in the task details (if specified).
    Dim customDetails As String = CStr(e.Node("Description"))
    e.Details = If((Not String.IsNullOrEmpty(customDetails)), customDetails, e.Details)
End Sub
Public Class TaskData
    Public Sub New(ByVal id As Integer)
        Me.id_Renamed = id
    End Sub
    Private id_Renamed As Integer
    Public ReadOnly Property Id() As Integer
        Get
            Return id_Renamed
        End Get
    End Property
    Public Property ShowInTimeline() As Boolean
    = False
    public Integer ParentId {get;set;}
    public String Name {get;set;}
    public String Description {get;set;}
    public DateTime StartDate {get;set;}
    public DateTime EndDate {get;set;}
    public static List(Of TaskData) InitData()
        Return New List(Of TaskData)() From {
            New TaskData(0) With {.Name = "Task A", .ParentId = 0, .StartDate = New Date(2023, 3, 1), .EndDate = New Date(2024, 3, 31)},
            New TaskData(1) With {.Name = "Task B", .ParentId = 0, .StartDate = New Date(2023, 3, 1), .EndDate = New Date(2023, 7, 1), .ShowInTimeline = True, .Description = "The description of Task B."},
            New TaskData(2) With {.ParentId = 0, .StartDate = New Date(2023, 7, 1), .EndDate = New Date(2023, 11, 1)}
        }
End Class