When you setup a hierarchical RadVirtualGrid and set the UseScrollbarsInHierarchy property to false and use VirtualGridAutoSizeColumnsMode.Fill for the child template, you expect that the column's width is calculated according to the total width of the respective template. Hence, if you shrink or enlarge the grid, the columns will shrink/enlarge respectively. However, if you double click the resize cursor between the column headers you will notice that the best-fit action is performed over the column and its width is adjusted. However, the VirtualGridAutoSizeColumnsMode.Fill setting is not respected and you either can't see all the columns, or you obtain some empty space if the column doesn't need much space. 

To reproduce: open the Demo application >> VirtualGrid >> First Look example. Follow the steps illustrated in the attached gif file. You will notice that when you expand a row, the "-" sign is show for a second and then it is returned to "+" although the row is still expanded. 

Workaround:
            this.radVirtualGrid1.CellFormatting += radVirtualGrid1_CellFormatting;
            this.radVirtualGrid1.RowExpanded += radVirtualGrid1_RowExpanded;
            this.radVirtualGrid1.RowCollapsed += radVirtualGrid1_RowCollapsed;



        private void radVirtualGrid1_RowCollapsed(object sender, VirtualGridRowExpandedEventArgs e)
        {
            if (expandedState.ContainsKey(e.RowIndex))
            {
                expandedState[e.RowIndex] = !expandedState[e.RowIndex];
            }
           
            this.radVirtualGrid1.TableElement.SynchronizeRow(e.RowIndex, true);
        }

        Dictionary<int, bool> expandedState = new Dictionary<int, bool>();

        private void radVirtualGrid1_RowExpanded(object sender, VirtualGridRowExpandedEventArgs e)
        {
            if (!expandedState.ContainsKey(e.RowIndex))
            {
                expandedState.Add(e.RowIndex, false);
            }
            expandedState[e.RowIndex] = !expandedState[e.RowIndex];
            this.radVirtualGrid1.TableElement.SynchronizeRow(e.RowIndex, true);
        }

        private void radVirtualGrid1_CellFormatting(object sender, Telerik.WinControls.UI.VirtualGridCellElementEventArgs e)
        {
            VirtualGridIndentCellElement indentCell = e.CellElement as VirtualGridIndentCellElement;
            if (indentCell != null)
            {
                if (expandedState.ContainsKey(e.CellElement.RowIndex) && expandedState[e.CellElement.RowIndex] == true)
                {
                    indentCell.ExpanderItem.SignImage = Properties.Resources.chevron_up;
                }
                else
                {
                    indentCell.ExpanderItem.SignImage = Properties.Resources.chevron_down;
                }
            }

        }

To reproduce: if you set the TableElement.RowHeight property, it affects the header row as well, but not all cells. As a result the header row overlaps the new row.

Workaround: set the TableElement.HeaderRowHeight as well.

  this.radVirtualGrid1.TableElement.HeaderRowHeight = 50;

To reproduce: use the following code snippet. Navigate to the last page and press the button to clear the rows. You will notice that the current page index remains 10 although no rows are available in the grid

        public RadForm1()
        {
            InitializeComponent();

            this.radVirtualGrid1.RowCount = 1000;
            this.radVirtualGrid1.ColumnCount = 5;
            this.radVirtualGrid1.CellValueNeeded += radVirtualGrid1_CellValueNeeded;

            this.radVirtualGrid1.EnablePaging = true;
        }

        private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
        {
            e.Value = "Item" + e.RowIndex + "." + e.ColumnIndex;
        }

        private void radButton1_Click(object sender, EventArgs e)
        {
            this.radVirtualGrid1.RowCount = 0;
            this.radVirtualGrid1.ColumnCount = 5; 
        }

Workaround:  this.radVirtualGrid1.VirtualGridElement.FindDescendant<VirtualGridPagingPanelElement>().PageNumberTextBox.Text = "1";

To reproduce: run the sample project and try to resize some of the columns.

RadVirtualGrid has 10 columns and 500 rows. You will notice the laggind while resizing the columns. Actually the number of the visible cells remains the same after the column's resizing. However, the CellValueNeeded event keeps firing.

A newly created grid has its CurrentCell property initialized to Nothing. Pressing [PageDown] or any other key that causes scrolling will crash.

Steps to Reproduce:
1. Launch application
2. Press [PageDown]

 Sub New() 
        InitializeComponent()

        Me.RadVirtualGrid1.ColumnCount = 50
        Me.RadVirtualGrid1.RowCount = 100
        AddHandler Me.RadVirtualGrid1.CellValueNeeded, AddressOf RadVirtualGrid1_CellValueNeeded
    End Sub

    Private Sub RadVirtualGrid1_CellValueNeeded(sender As Object, e As Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs)
        e.Value = e.ColumnIndex
    End Sub

Workaround: 

Me.RadVirtualGrid1.CurrentCell = New Telerik.WinControls.UI.VirtualGridCellInfo(0, 0, Me.RadVirtualGrid1.MasterViewInfo)

I miss grouping functionality in VirtualGrid. In my opinion, the following process would be conceivable:
1. user interaction triggers an event - e. g. GroupChanged (similar to FilterChanged).
2. This event determines all available groups and returns them to the VirtualGrid. 
3. if the user expand a group > a second event is fired - and returns all matching data rows.

To reproduce:
- Enable the paging and add 1000 rows.
- Press Ctrl + End
- An exception is thrown.

Workaround:

radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleEndKey(KeyEventArgs keys)
    {
        this.GridElement.PageIndex = this.GridElement.TotalPages - 1;
      
        return true;
        //return base.HandleEndKey(keys);
    }
}

The attached gif file illustrates how to reproduce the problem with the Demo application. 

Use attached to reproduce (just start it and press enter).

Workaround:

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleEnterKey(KeyEventArgs keys)
    {
        if (this.GridElement.CurrentCell != null)
        {
            return base.HandleEnterKey(keys);
        }
        return false; 
    }
}


radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

Workaround:
this.radVirtualGrid1.RowCount += 100;
this.radVirtualGrid1.TableElement.PagingPanelElement.UpdateView();

To reproduce:
void radButton1_Click(object sender, EventArgs e)
{
    this.radVirtualGrid1.CurrentCell = null;
}

Workaround:

class MyRadVirtualGrid : RadVirtualGrid
{
    protected override void CreateChildItems(RadElement parent)
    {
        base.CreateChildItems(parent);
        parent.Children.RemoveAt(0);
        var field = typeof(RadVirtualGrid).GetField("virtualGridElement", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        var element = new MyVirtualGridElement();
        field.SetValue(this,element);

        
        parent.Children.Add(element);
    }
}
class MyVirtualGridElement : RadVirtualGridElement
{
    protected override Type ThemeEffectiveType
    {
        get { return typeof(RadVirtualGridElement); }
    }
    protected override bool SetCurrentCell(VirtualGridCellInfo value)
    {
        if (value == null)
        {
            if (this.IsInEditMode && !this.EndEdit())
            {
                return false;
            }

            int row = int.MinValue;
            VirtualGridViewInfo viewInfo = null;

            if (this.CurrentCell != null)
            {
                row = this.CurrentCell.RowIndex;
                viewInfo = this.CurrentCell.ViewInfo;
            }

            if (this.CurrentCell != null && (value == null || this.CurrentCell.ViewInfo != value.ViewInfo || this.CurrentCell.RowIndex != value.RowIndex))
            {
                VirtualGridRowValidatingEventArgs e = new VirtualGridRowValidatingEventArgs(row, viewInfo);
                this.OnRowValidating(e);

                if (e.Cancel)
                {
                    return false;
                }
            }
            var currentCell = typeof(RadVirtualGridElement).GetField("currentCell", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
            currentCell.SetValue(this, value);

            if (this.CurrentCell != null)
            {
                this.EnsureCellVisible(this.CurrentCell.RowIndex, this.CurrentCell.ColumnIndex, this.CurrentCell.ViewInfo);
            }

            VirtualGridTableElement tableElement = null;

            if (this.CurrentCell != null)
            {
                tableElement = this.GetTableElement(this.CurrentCell.ViewInfo);
            }
            else
            {
                tableElement = this.TableElement;
            }
            

            if (tableElement != null)
            {
                VirtualGridRowElement rowElement = tableElement.ViewElement.GetRowElement(row);

                if (rowElement != null)
                {
                    rowElement.Synchronize(false);
                }
            }

            if (value != null)
            {
                tableElement = this.GetTableElement(value.ViewInfo);
                if (tableElement != null)
                {
                    VirtualGridRowElement rowElement = tableElement.ViewElement.GetRowElement(value.RowIndex);

                    if (rowElement != null)
                    {
                        rowElement.Synchronize(false);
                    }
                }
            }

            if (viewInfo != null)
            {
                VirtualGridRowEventArgs args = new VirtualGridRowEventArgs(row, viewInfo);
                this.OnRowValidated(args);
            }

            this.OnCurrentCellChanged(EventArgs.Empty);

            return true;
        }
        return base.SetCurrentCell(value);
    }
}

Using RadVirtualGrid, I have a requirement for showing hierarchical levels of data. The parent level and child levels share the SAME column headers.  I am utilizing the QueryHasChildRows event of the grid to set the number of rows for each hierarchical level. In that event I set a few properties to control how a child view is rendered as below:

            else if (e.ViewInfo.HierarchyLevel > 0)
            {
                var items = ((IList<AllocStructNode>)e.ViewInfo.ParentViewInfo.Tag)[e.ViewInfo.ParentRowIndex];
                if (items.Children != null && items.Children.Count > 0)
                {
                    e.ViewInfo.Tag = items.Children;
                    e.ViewInfo.RowCount = items.Children.Count;
                    e.ViewInfo.HeaderRowHeight = 0;
                    e.ViewInfo.ShowHeaderRow = false;
                    e.ViewInfo.FilterRowHeight = 0;
                    e.ViewInfo.ShowFilterRow = false;
                    e.ViewInfo.Padding = new Padding(0);
                    e.ViewInfo.HorizontalScrollState = ScrollState.AlwaysHide;
                }
            }


When a new level is rendered, a new demarcated section of child table element with its own horizontal scrolling displayed. When the parent is horizontally scrolled, the child level doesn't scroll (not synchronized). Similarly, when the child is horizontally scrolled, the parent does not scroll as well.

Workaround:
See attached project.

Scenario to cover: the user tries to filter the grid not with each entered symbol but when the value in the filter cell is committed (Enter key is pressed) and the editor is closed. The CellValuePushed event is fired only for data cells and the FilterChanged event is fired with each keystroke but not when the editor is closed. A similar scenario is valid for the new row. There is no suitable event for capturing when a certain cell is updated in the new row as well.

To reproduce:
- Remove the default padding:

private void RadVirtualGrid1_RowExpanding(object sender, VirtualGridRowExpandingEventArgs e)
{
     e.ChildViewInfo.Padding =new Padding(0,0,0,0);
 
}

Still some space remains, this can be seen in the demo application as well.

To reproduce:
private void RadVirtualGrid1_EditorRequired(object sender, Telerik.WinControls.UI.VirtualGridEditorRequiredEventArgs e)
{
    switch (e.ColumnIndex)
    {
        case 1:
            {
                VirtualGridTextBoxControlEditor editor = new VirtualGridTextBoxControlEditor();
                editor.CharacterCasing = CharacterCasing.Upper;
                e.Editor = editor;
            }
            break;
    }
}

- Open the editor and try using the backspace or the arrow keys. 

Workaround:
class MyGrid : RadVirtualGrid
{
    protected override void OnKeyDown(KeyEventArgs e)
    {
        base.OnKeyDown(e);

        if (this.ActiveEditor is VirtualGridTextBoxControlEditor)
        {
            var editor = this.ActiveEditor as VirtualGridTextBoxControlEditor;
            var element =   editor.EditorElement as RadTextBoxControlElement;
            element.InputHandler.ProcessKeyDown(e);
        }
    }
    protected override void OnKeyUp(KeyEventArgs e)
    {
        base.OnKeyUp(e);

        if (this.ActiveEditor is VirtualGridTextBoxControlEditor)
        {
            var editor = this.ActiveEditor as VirtualGridTextBoxControlEditor;
            var element = editor.EditorElement as RadTextBoxControlElement;
            element.InputHandler.ProcessKeyUp(e);
        }
    }
}