When the RadGridView is filtered you can get all items in the data view using the Items collection property of the control. The count can be accessed with the gridView.Items.Count property.

If the RadGridView is grouped and then filtered, the Items.Count no longer returns the correct value. The count doesn't take into account the items that are in collapsed groups. Instead the count contains only the expanded group objects.

To work this around, use the following code instead of gridView.Items.Count.

int count = gridView.Items.OfType<object>().Count(); 

The selection with the Shift key when SelectionMode=Extended no longer works in the default Nested rendering mode of RadGridView. This reproduces only when the data view is grouped.

To work this around, set the GroupRenderMode property of RadGridView to Flat.

<telerik:RadGridView GroupRenderMode="Flat" />

Currently the filters for the RadGridView only allows 2 filters. It would be very helpful for the default filter popout to have the option to add additional filters.

Current filter popout:

Filter popout with ability to add additional filters via an Add Filter button:

Competitor's GridView controls have this feature already and it would be very useful to have this feature on the RadGridView control. 

The cell content gets clipped when the width of the previous column changes at runtime. This happens in the Windows11 and Office2019 themes (possibly in others) and only if the clipped cell is position before the right frozen columns area.

To work this around, you can call the Rebind() method of RadGridView, after the column width changes.

The Clear Filters option in the FieldFilterControl cannot be selected when the DefaultOperator1 is set in the FilterOperatorsLoading event of RadGridView. The FieldFilterControl is the element shown under the column header when the FilteringMode property of RadGridView is set to FilterRow. Setting e.DefaulteOperator1 in the FilterOperatorsLoading properly selects the corresponding filter in the drop down, but after that you cannot select Clear Filters when clicking on this option.

To work this around, you can use the CellLoaded event instead of FilterOperatorsLoading. This will allow you to get the FieldFilterControlViewModel and set its SelectedOperatorViewModel property.

private void manualGridView_CellLoaded(object sender, CellEventArgs e)
{
    if (e.Cell is GridViewHeaderCell && e.Cell.Column.UniqueName == "MyColumn")
    {
        Dispatcher.BeginInvoke(new Action(() =>
        {
            var fieldFilter = e.Cell.FindChildByType<FieldFilterControl>();
            var viewModel = (FieldFilterControlViewModel)fieldFilter.DataContext;
            viewModel.SelectedOperatorViewModel = viewModel.AvailableOperatorViewModels.FirstOrDefault(x => x.FilterOperator == FilterOperator.IsLessThan);
        }));
    }
}

The height of the column footer is not updated properly to autofit the footer's content. Actually, this works when the footer content becomes bigger than the current (or the default) value, but if you change the content with a smaller one, the bigger height remains. In other words, the footer height autofits when the content becomes bigger but it doesn't decrease when the content becomes smaller after that.

private void gridView_CellLoaded(object sender, CellEventArgs e)
{
    if (e.Cell is GridViewFooterCell)
    {
        var row = e.Cell.ParentRow;
        Dispatcher.BeginInvoke(new Action(() =>
        {
            var aggregatesList = row.ChildrenOfType<AggregateResultsList>(); // the exact type of children that should be used to get the new height may vary based on your column Footer contents
            if (aggregatesList.Count() > 0)
            {
                var height = aggregatesList.Max(x => x.ActualHeight);

                var cellsPanel = e.Cell.ParentOfType<GridViewCellsPanel>();
                PropertyInfo minRowHeightProp = cellsPanel.GetType().GetProperty("MinRowHeight", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
                object minRowHeightPair = minRowHeightProp.GetValue(cellsPanel);
                PropertyInfo heightProp = minRowHeightPair.GetType().GetProperty("Second");
                heightProp.SetValue(minRowHeightPair, height);
            }
        }));
    }
}