If you refresh an object set property of entity context, the RadGridView is not updated. 

The sample code below does not work:

this.radGridView1.DataSource = entities.Countries;

int maxId = (from c in entities.Countries
                         orderby c.Id descending
                         select c.Id).First();

            Country country = new Country();
            country.Id = maxId + 1;
            country.Name = Path.GetRandomFileName();
            entities.Countries.AddObject(country);
            entities.SaveChanges(System.Data.Objects.SaveOptions.AcceptAllChangesAfterSave);

            entities.Refresh(System.Data.Objects.RefreshMode.StoreWins, entities.Countries);

To reproduce:
void radGridView1_CurrentRowChanged(object sender, Telerik.WinControls.UI.CurrentRowChangedEventArgs e)
        {
            e.CurrentRow.Cells[2].ColumnInfo.IsCurrent = true;
        }

We should consider the Display attribute when using business objects as data source in RadGridView.

To reproduce:
void grid_RowValidating(object sender, RowValidatingEventArgs e)
{
    e.Cancel = true;
}

Pressing the escape key should cancel the edit mode and revert the value

- Create a new project containing RadGridView
- Build hierarchy with large text data in cells
- Set the AutoSizeRows property to true and AutoSizeColumnMode to Fill
- Run the project, scroll down and try to click on a cell

Steps to reproduce:
1. Add a grid to a form and make it read only
2. Add a masked box column and set the mask
3. Add some data and run the project
You will see that the mask is not applied to the values in the mask box column
Comment: This is not an issue.  The mask is applied after editing the text with RadMaskedEditBox, in read-only mode there is no masked editor created. You should use the conversion layer in RadGridView to solve the issue. Check the GridView >> Manipulated Data >> Convert Values example from our demo application.

To reproduce:
- add RadGridView and fill it with data;
- use the following code for saving the layout: string layout;
using (MemoryStream ms = new MemoryStream())
{
    radGridView1.SaveLayout(ms);
    ms.Position = 0;
    byte[] buffer = new byte[ms.Length - 1];

    ms.Read(buffer, 0, buffer.Length);
    layout = Convert.ToBase64String(buffer);
    ms.Close();
}

When you try to load the saved layout, using the following code, DataException is thrown:
using (MemoryStream stream = new MemoryStream(Convert.FromBase64String(layout)))
{
    radGridView1.LoadLayout(stream);
}

Workaround: save the layout in xml file

Makes RadGridView to be thread safe by using from BackgroundWorker

1. Create a new project with RadGridView.
2. Bind it and set grouping.
3. Add a summary row and set ShowParentGroupSummaries property to true.
4. Handle the ViewCellFormatting event and set all summary rows to be IsVisible = false when the processed cell is GridSummaryCellElement:

void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.CellElement is GridSummaryCellElement)
    {
        e.Row.IsVisible = false;
    }
}

CORRECT WAY TO HANDLE THIS CASE:
Hide the summary rows in the groups you want after grouping/data binding.
To hide the first bottom summary row of the first group in a RadGridView use the following code:
this.radGridView1.Groups[0].GroupRow.BottomSummaryRows[0].IsVisible = false;

I have a GridView (Winforms v. 2017.3.1017.40, same problem with 2017.2.502.40) configured as on the attached screenshot (made some groups, made a search, and used the "excel-like" filter on a column to uncheck some values).

Then I try to click on some column headers to sort the grid.
After a few clicks, I get this error :
InvalidOperationException: La collection a été modifiée ; l'opération d'énumération peut ne pas s'exécuter.

I got different stacktrace with the same error :
InvalidOperationException: La collection a été modifiée ; l'opération d'énumération peut ne pas s'exécuter.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
   at System.Collections.Generic.List`1.Enumerator.MoveNext()
   at Telerik.WinControls.UI.DataGroup.<GetEnumerator>d__0.MoveNext()
   at Telerik.WinControls.UI.GridViewGroupRowInfo.get_ChildRows()
   at Telerik.WinControls.UI.GridViewRowInfo.HasChildRows()
   at Telerik.WinControls.UI.PrintGridTraverser.CanStepInHierarchy()
   at Telerik.WinControls.UI.GridTraverser.StepInHierarchy()
   at Telerik.WinControls.UI.GridTraverser.MoveNextCore()
   at Telerik.WinControls.UI.GridTraverser.MoveNext()
   at Telerik.WinControls.UI.GridViewSearchRowInfo.worker_DoWork(Object sender, DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

-----

InvalidOperationException: Failed to compare two elements in the array. ---> NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.WinControls.UI.GridViewRowInfoComparer.CompareRows(GridViewRowInfo x, GridViewRowInfo y, SortDescriptorCollection context)
   at System.Collections.Generic.ArraySortHelper`1.InternalBinarySearch(T[] array, Int32 index, Int32 length, T value, IComparer`1 comparer)
   at System.Collections.Generic.ArraySortHelper`1.BinarySearch(T[] array, Int32 index, Int32 length, T value, IComparer`1 comparer)


   --- End of inner exception stack trace ---
   at System.Collections.Generic.ArraySortHelper`1.BinarySearch(T[] array, Int32 index, Int32 length, T value, IComparer`1 comparer)
   at System.Collections.Generic.List`1.BinarySearch(Int32 index, Int32 count, T item, IComparer`1 comparer)
   at Telerik.Collections.Generic.HybridIndex`1.PerformWithQuickSort()
   at Telerik.Collections.Generic.HybridIndex`1.get_Items()
   at Telerik.Collections.Generic.Index`1.GetEnumerator()
   at Telerik.WinControls.Data.GroupBuilder`1.Perform(IReadOnlyCollection`1 items, Int32 level, Group`1 parent)
   at Telerik.WinControls.Data.GroupBuilder`1.get_Groups()
   at Telerik.WinControls.UI.GridViewInfo.Refresh()
   at Telerik.WinControls.UI.GridViewInfo.get_ChildRows()
   at Telerik.WinControls.UI.ViewInfoTraverser.SetCollectionForStage(Boolean initializeCollection)
   at Telerik.WinControls.UI.ViewInfoTraverser.ChangeCollectionForward()
   at Telerik.WinControls.UI.ViewInfoTraverser.MoveNextCore()
   at Telerik.WinControls.UI.ViewInfoTraverser.MoveNext()
   at Telerik.WinControls.UI.GridTraverser.MoveNextCore()
   at Telerik.WinControls.UI.GridTraverser.MoveNext()
   at Telerik.WinControls.UI.BaseGridNavigator.NavigateToRow(GridViewRowInfo row, Boolean select)
   at Telerik.WinControls.UI.BaseGridNavigator.ProcessViewChangedEvent(GridViewEvent eventData)
   at Telerik.WinControls.UI.BaseGridNavigator.ProcessEventCore(GridViewEvent eventData)
   at Telerik.WinControls.UI.GridViewEventProcessEntity.ProcessCollection(GridViewEvent gridEvent, PriorityWeakReferenceList list, GridEventProcessMode processMode)
   at Telerik.WinControls.UI.GridViewEventProcessEntity.ProcessEvent(GridViewEvent gridEvent)
   at Telerik.WinControls.UI.GridViewSynchronizationService.NotifyListeners(GridViewEvent gridEvent)
   at Telerik.WinControls.UI.GridViewSynchronizationService.FlushEvents()
   at Telerik.WinControls.UI.GridViewSynchronizationService.DispatchEvent(GridViewEvent gridEvent)
   at Telerik.WinControls.UI.GridViewSynchronizationService.DispatchEvent(GridViewTemplate template, GridViewEvent eventData, Boolean postUI)
   at Telerik.WinControls.UI.GridViewTemplate.DispatchDataViewChangedEvent(Object sender, DataViewChangedEventArgs args)
   at Telerik.WinControls.UI.GridViewTemplate.OnViewChanged(Object sender, DataViewChangedEventArgs e)
   at Telerik.WinControls.UI.MasterGridViewTemplate.OnViewChanged(Object sender, DataViewChangedEventArgs e)
   at Telerik.WinControls.Data.RadDataView`1.RebuildData(Boolean notify)
   at Telerik.WinControls.Data.RadDataView`1.OnNotifyPropertyChanged(PropertyChangedEventArgs e)
   at Telerik.WinControls.Data.RadCollectionView`1.OnNotifyPropertyChanged(String propertyName)
   at Telerik.WinControls.UI.GridViewSortDescriptorCollection.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
   at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e)
   at Telerik.WinControls.Data.SortDescriptor.set_Direction(ListSortDirection value)
   at Telerik.WinControls.UI.GridViewColumn.Sort(RadSortOrder sortOrder, Boolean multiSortMode)
   at Telerik.WinControls.UI.GridHeaderCellElement.Sort(RadSortOrder sortOrder)
   at Telerik.WinControls.UI.GridHeaderRowBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.UI.BaseGridBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.UI.RadGridView.OnMouseUp(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at Telerik.WinControls.RadControl.WndProc(Message& m)
   at Telerik.WinControls.UI.RadGridView.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

------

InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
   at System.Collections.Generic.List`1.Enumerator.MoveNext()
   at Telerik.WinControls.UI.DataGroup.<GetEnumerator>d__0.MoveNext()
[...]
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Alto.Client.Controls.Dispatch.DispatchResources.DeliveryPointFilterManager.get_DeliveryPointsVisible() in d:\Builds\45153\Alto\Alto.Prod\src\Alto\Alto.Client\Controls\Dispatch\DispatchResources\DeliveryPointFilterManager.cs:line 38
   at Alto.Client.Controls.Dispatch.DispatchResources.UcDeliveryPoint.get_Title() in d:\Builds\45153\Alto\Alto.Prod\src\Alto\Alto.Client\Controls\Dispatch\DispatchResources\UcDeliveryPoint.cs:line 1520
   at Alto.Client.Controls.Dispatch.DispatchResources.UcDeliveryPoint.updatePanelTitle() in d:\Builds\45153\Alto\Alto.Prod\src\Alto\Alto.Client\Controls\Dispatch\DispatchResources\UcDeliveryPoint.cs:line 543
   at Alto.Client.Controls.Dispatch.DispatchResources.UcDeliveryPoint.onFilterChanged(Object sender, GridViewCollectionChangedEventArgs e) in d:\Builds\45153\Alto\Alto.Prod\src\Alto\Alto.Client\Controls\Dispatch\DispatchResources\UcDeliveryPoint.cs:line 547
   at Telerik.WinControls.UI.GridViewCollectionChangedEventHandler.Invoke(Object sender, GridViewCollectionChangedEventArgs e)
   at Telerik.WinControls.UI.RadGridView.OnFilterChanged(Object sender, GridViewCollectionChangedEventArgs e)
   at Telerik.WinControls.UI.EventDispatcher.RaiseEvent[T](Object eventKey, Object sender, T args)
   at Telerik.WinControls.UI.GridViewFilterDescriptorCollection.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
   at Telerik.Collections.Generic.NotifyCollection`1.InsertItem(Int32 index, T item)
   at Telerik.WinControls.UI.GridViewFilterDescriptorCollection.InsertItem(Int32 index, FilterDescriptor item)
   at System.Collections.ObjectModel.Collection`1.Add(T item)
   at Telerik.WinControls.UI.GridViewDataColumn.SetFilterDescriptor(FilterDescriptor value)
   at Telerik.WinControls.UI.GridHeaderCellElement.filterPopup_FilterConfirmed(Object sender, EventArgs e)
   at Telerik.WinControls.UI.BaseFilterPopup.OnFilterConfirmed()
   at Telerik.WinControls.UI.RadListFilterPopup.OnButtonOkClick(EventArgs e)
   at Telerik.WinControls.UI.RadListFilterPopup.ButtonOK_Click(Object sender, EventArgs e)
   at Telerik.WinControls.RadElement.OnClick(EventArgs e)
   at Telerik.WinControls.UI.RadButtonItem.OnClick(EventArgs e)
   at Telerik.WinControls.UI.RadButtonElement.OnClick(EventArgs e)
   at Telerik.WinControls.RadElement.DoClick(EventArgs e)
   at Telerik.WinControls.RadElement.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadItem.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.RaiseRoutedEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadItem.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.RaiseRoutedEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.DoMouseUp(MouseEventArgs e)
   at Telerik.WinControls.ComponentInputBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.RadControl.OnMouseUp(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at Telerik.WinControls.RadControl.WndProc(Message& m)
   at Telerik.WinControls.UI.RadPopupControlBase.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

----

InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
   at Telerik.WinControls.UI.DataGroup.<GetEnumerator>d__0.MoveNext()
   at Telerik.WinControls.Data.GroupBuilder`1.Perform(IReadOnlyCollection`1 items, Int32 level, Group`1 parent)
   at Telerik.WinControls.Data.DataItemGroup`1.get_Groups()
   at Telerik.WinControls.UI.DataGroup.get_Groups()
   at Telerik.WinControls.UI.GridViewTemplate.InvalidateSummaryRowsCore(DataGroup group, Boolean invalidateChildren)
   at Telerik.WinControls.UI.GridViewTemplate.InvalidateSummaryRowsCore(DataGroup group, Boolean invalidateChildren)
   at Telerik.WinControls.UI.GridViewTemplate.InvalidateGroupSummaryRows(DataGroup group, Boolean invalidateChildren)
   at Telerik.WinControls.UI.GridViewTemplate.RefreshSummaryRowsInGroup(NotifyCollectionChangedEventArgs e)
   at Telerik.WinControls.UI.GridViewTemplate.RefreshAggregates(NotifyCollectionChangedEventArgs e)
   at Telerik.WinControls.UI.MasterGridViewTemplate.OnViewChanged(Object sender, DataViewChangedEventArgs e)
   at Telerik.WinControls.Data.RadDataView`1.RebuildData(Boolean notify)
   at Telerik.WinControls.Data.RadDataView`1.OnNotifyPropertyChanged(PropertyChangedEventArgs e)
   at Telerik.WinControls.Data.RadCollectionView`1.OnNotifyPropertyChanged(String propertyName)
   at Telerik.WinControls.UI.GridViewSortDescriptorCollection.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
   at Telerik.WinControls.UI.GridViewSortDescriptorCollection.RemoveItem(Int32 index)
   at Telerik.WinControls.UI.GridViewColumn.Sort(RadSortOrder sortOrder, Boolean multiSortMode)
   at Telerik.WinControls.UI.GridHeaderCellElement.Sort(RadSortOrder sortOrder)
   at Telerik.WinControls.UI.GridHeaderRowBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.UI.BaseGridBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.UI.RadGridView.OnMouseUp(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at Telerik.WinControls.RadControl.WndProc(Message& m)
   at Telerik.WinControls.UI.RadGridView.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

When you set a RadGridView's SelectionMode to GridViewSelectionMode.CellSelect and then you highlight full rows by using the row header, the SelectedRows collection is empty.  Telerik support informed me this is "as expected" and that I should use "SelectedCells" collection when using the CellSelect Mode.  While this is a decent workaround I don't see why SelectedRows collection can't be filled when the entire row is actually highlighted.  

To reproduce: please refer to the attached sample project. 

Workaround:   this.radGridView1.TableElement.ScrollToRow(this.radGridView1.RowCount-1);

ADD. RadGridView - SelectLastAddedRow should work in scenarios when user adds row too, not only by adding rows from the datasource.
Comment - the property is intended to work only for added rows in the RadGridView DataSource. For the rest of the cases, the cases, the UserAddedRow event should be handled.

The DefaultValueAttribute of Format and FormatInfo properties of GridViewDataColumn causes exceptions when load layout is performed.
Comment: this is an issue inside .Net framework.

To reproduce:

Add a RadGridView and bind it to a DataTable.

Subscribe to the TableElement's vertical scroll's ValueChanged event and add new data when the value reaches the maximum:

private void RequestData(int startFrom, int count) { for (int i = 0; i < count; i++) { DataRow row = dt.NewRow(); row["ID"] = startFrom + i; dt.Rows.Add(row); } } private void VScrollBar_ValueChanged(object sender, EventArgs e) { if (dgwData.TableElement.VScrollBar.Value + dgwData.TableElement.VScrollBar.LargeChange >= dgwData.TableElement.VScrollBar.Maximum) { int maxVScrollBarBefore = dgwData.TableElement.VScrollBar.Maximum; dgwData.SelectionChanged -= dgwData_SelectionChanged; dgwData.TableElement.VScrollBar.ValueChanged -= VScrollBar_ValueChanged; RequestData(dt.Rows.Count, rowsToCharge); dgwData.SelectionChanged += dgwData_SelectionChanged; dgwData.TableElement.VScrollBar.ValueChanged += VScrollBar_ValueChanged; } }

You will notice that when you use the mousewheel the scrollbar is being updated, but when you use the arrows it is not.

Workaround: Invoke the UpdateScrollRange method of the TableElement's RowScroller after adding the new data: dgwData.TableElement.RowScroller.UpdateScrollRange();

The format specifier 'tt' in the ExcelExportFormatString property should be outputed as 'AM' or 'PM'.
For the formatting to work correctly the users have to set the property to Excel format codes not .NET format strings.
Here is the list of excel's format  codes: http://office.microsoft.com/en-us/excel-help/number-format-codes-HP005198679.aspx

This is not considered an issue, it is how RadGridView works. Here are more details:

In order for a GridDetailViewCellElement  to display a pageview instead of a single table element, either the template of the row holding it has to have more than one child template, or its ShowChildViewCaptions should be true.
Once there is a page view, the tabs in it will be visible at all times, except when some of the templates has no rows and AllowAddNewRow for it is false – if it does not have any rows and the user cannot add row, it is considered that there is no need from it.
If one needs to change the visibility of the tabs, this can be done in the ViewCellFormatting event:
private void RadGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
	GridDetailViewCellElement detailCell = e.CellElement as GridDetailViewCellElement;

	if (detailCell != null) {
		foreach (RadPageViewItem item in detailCell.PageViewElement.Items) {
			item.Visibility = Telerik.WinControls.ElementVisibility.Visible;
		}
	}
}

The conditional formatting collection get deleted after closing the property builder.

To reproduce :

Add a gridview with a datasource.
Open property builder
Select a column
Advance -> ConditionalFormattingObjectList
Add a expression, set a name
Press Ok

If you click the ConditionalFormattingObjectList, you can see the expression

If you click close the Property Builder, the list is not saved when you open it again.