Private Sub grd_ContextMenuOpening(sender As Object, e As ContextMenuOpeningEventArgs) Handles grd.ContextMenuOpening
        Dim i As Integer = 0
        Dim IgnoreOperator() As String = {"Ends with", "Equals", "not equal to", "no filter"}
        If DirectCast(e.ContextMenuProvider, Telerik.WinControls.UI.GridCellElement).ColumnInfo.FieldName = "AcctNbr" Then
            While i < e.ContextMenu.Items.Count
                If Not IgnoreOperator.Contains(e.ContextMenu.Items(i).Text, StringComparer.CurrentCultureIgnoreCase) Then
                    e.ContextMenu.Items(i).Visibility = Telerik.WinControls.ElementVisibility.Collapsed
                End If
                i = i + 1
            End While
        End If
    End Sub

Private Sub grd_FilterChanging(sender As Object, e As GridViewCollectionChangingEventArgs) Handles grd.FilterChanging
        dv.RowFilter =""
        If e.NewValue IsNot Nothing
        If DirectCast((DirectCast(e.NewItems, Object())(0)), Telerik.WinControls.Data.FilterDescriptor).[Operator] = Telerik.WinControls.Data.FilterOperator.IsEqualTo AndAlso DirectCast((DirectCast(e.NewItems, Object())(0)), Telerik.WinControls.Data.FilterDescriptor).PropertyName = "AcctNbr" Then
            Dim CurrentVal As String = CStr(e.NewValue)
            dv.RowFilter = "EnAcctNbr ='" & CurrentVal & "'"
        End If
        If DirectCast((DirectCast(e.NewItems, Object())(0)), Telerik.WinControls.Data.FilterDescriptor).[Operator] = Telerik.WinControls.Data.FilterOperator.IsNotEqualTo AndAlso DirectCast((DirectCast(e.NewItems, Object())(0)), Telerik.WinControls.Data.FilterDescriptor).PropertyName = "AcctNbr" Then
            Dim CurrentVal As String = CStr(e.NewValue)
            dv.RowFilter = "EnAcctNbr <>'" & CurrentVal & "'"
        End If
        End If

        private void tbVisibleResourceCount_ValueChanged(object sender, EventArgs e)
        {
            if (DesignMode)
                return;

            try
            {
                int val = (int) tbVisibleResourceCount.Value;

                if (val <= 0)
                {
                    tbVisibleResourceCount.Value = 1;
                }
                else
                {
                    var newValue = Math.Min(val, AppointmentsVm?.AktiveRessourcen?.Count ?? 0 /*rsTermine.Resources.Count*/);

                    /* todo
                    switch (rsTermine.SchedulerElement.ViewElement)
                    {
                        case SchedulerTimelineViewElement timelineElement:                           
                            break;
                    
                        case SchedulerDayViewElement dayViewElement:
                            break;

                        case SchedulerMonthViewElement monthViewElement:
                            break;

                        case TimelineGroupingByResourcesElement timelineGrouped:
                            IList<SchedulerTimelineViewElement> childTimelineElements = timelineGrouped.GetChildViewElements();
                            break;

                        case SchedulerDayViewGroupedByResourceElement dayViewGrouped:
                            break;

                        case SchedulerMonthViewGroupedByResourceElement monthViewGrouped:
                            break; 
                    }*/

                    rsTermine.ActiveView.ResourcesPerView = newValue;
                }

                SetAppointmentsMargin();
                _adjustBackgroundsTimer?.Reset();
            }
            catch (Exception ex)
            {
                LogHelper.HandleError<CalendarView>(this, $"Fehler in {nameof(tbVisibleResourceCount_ValueChanged)}", ex);
            }
        }

public partial class Form1 : Form
    {

        private int parentRows = 4;
        private int parentColumns = 4;

        private int childRows = 2;
        private int childColumns = 6;

        public Form1()
        {
            InitializeComponent();

            this.grid.CellValueNeeded += (s, e) =>
            {
                if (e.ViewInfo == this.grid.MasterViewInfo)
                {
                    if (e.ColumnIndex < 0) return;
                    else if (e.RowIndex == RadVirtualGrid.HeaderRowIndex)
                    {
                        e.Value = "HEADER_" + e.ColumnIndex;
                    }

                    else if (e.RowIndex < 0)
                    {
                        e.Value = "FIELD_" + e.ColumnIndex;
                    }

                    else if (e.RowIndex >= 0 && e.RowIndex < parentRows)
                    {
                        e.Value = "Value (" + e.RowIndex + ";" + e.ColumnIndex + ")";
                    }
                }
                else
                {

                    if (e.ColumnIndex < 0) return;
                    else if (e.RowIndex == RadVirtualGrid.HeaderRowIndex)
                    {
                        e.Value = "CHILD_HEADER_" + e.ColumnIndex;
                    }

                    else if (e.RowIndex < 0)
                    {
                        e.Value = "CHILD_FILED_ " + e.ColumnIndex;
                    }

                    else if (e.RowIndex >= 0 && e.RowIndex < childRows)
                    {
                        e.Value = "Child_Value (" + e.RowIndex + ";" + e.ColumnIndex + ")";
                    }

                }
            };

            this.grid.QueryHasChildRows += (s, e) =>
            {
                e.HasChildRows = e.ViewInfo == this.grid.MasterViewInfo && e.RowIndex >= 0 && e.RowIndex < parentRows;
            };

            this.grid.RowExpanding += (s, e) =>
            {
                e.ChildViewInfo.ColumnCount = childColumns;
                e.ChildViewInfo.RowCount = childRows;
            };


            this.grid.RowCount = parentRows;
            this.grid.ColumnCount = parentColumns;
        }
    }