- Async parse of single xml file to speed-up the import
- Allow to import only part of the file
- Respect the widths of the columns and row heights and do not measure them first time in the WorksheetLayout or measure them for the current Viewport only
- Inserting rows/columns also need improvements in terms of performance.

if you use Excel, you use a lot of formulas. 
But In Telerik WPF there isn't enough formulas.(even like SUMIFS , SUBTOTAL) 

But I search for other library like Kendo-UI, there is more fomulas than WPF. 
Why are these different? 

Please make this formulas in your library.

The class would be used for customization of the printing behavior of the control.

Expose WorksheetUIUpdateContextBase.GetDataValidationRuleResult(CellIndex). This method is useful for creating optimized custom Data Validation Circles layers.

Available in LIB Version 2017.2.828.

Implement automatic completion of cell value based on the values typed above, in the same column.

Setting the visible size property to a small number, like 10,10, will result in missing the last column right border and last row bottom border.

If a worksheet spans more than one page, you can print row and column headings or labels (also called print titles) on every page to ensure that the data is properly labeled.
Duplicate of SpreadProcessing: Repeat specific rows or columns on every printed page (telerik.com)

NullReferenceException is thrown when the VisibleSize property of RadSpreadsheet is set more than once on two (or more) adjacent lines. For example:

spreadsheet.VisibleSize = new SizeI(1, 1);
spreadsheet.VisibleSize = new SizeI(5, 5);

To work this around you can increase the time between the settings of the VisibleSize property. For example you can use the ActiveSheetEditorChanged event of RadSpreadsheet and the ActivePresenterChanged event of the ActiveWorksheetEditor, and the UIUpdated event of the ActivePresenter. Each time the VisibleSize is changed, the ActiveWorksheetEditor will be recreated along with its ActivePresenter. You should make sure the second, third, etc. setting of the VisibleSize is executed after the new ActivePresenter is loaded. This can be done in the UIUpdated event.

When a de-DE culture is applied the 1,1 should be parsed as a number. On the other hand the 1.1 (with a dot) should be parsed as 01.Jan. Currently, both values (1,1 and 1.1) are parsed as datetime.

Decline reason: This is reproducible only if the cell was previously formatted as DateTime. In this case the separator is not taken into account which is expected. The same behavior can be observed also in Excel.

When the VisibleSize property of the spreadsheet control is set (for example new SizeI(10, 10)) and column is selected via its header (click on it), the IsColumnSelection property of the ActiveWorksheetEditor's Selection returns False. This applies also for the IsRowSelection property.

If you try to filter a column which contains a cell with applied font color and the project is run in debug mode with enabled C# exceptions, it throws ArgumentException at System.Windows.Media.ColorConverter.ConvertFrom(ITypeDescriptorContext td, CultureInfo ci, Object value). The exception is handled and the functionality is working as expected, however this may be annoying during debugging projects containing RadSpreadsheet.

If you begin entering e.g. "=" in FormulaBar, the characters are not visible in dark themes. If the focus is in the cell it works as expected, if the focus is in FormulaBar, the Foreground is dark and cannot be seen on dark background. 

Workaround:
-  set the following style (add BaseOn if using implicit styles)

<Style  TargetType="spreadsheetControls:RadSpreadsheetFormulaBar" BasedOn="{StaticResource RadSpreadsheetFormulaBarStyle}">
            <Setter Property="Foreground" Value="White"/>
</Style>

Available in LIB Version 2017.2.828.

Through the sorting options, the user can set sort orientation (to sort by rows or by columns) and whether the sort should be case sensitive.

If you need to set a custom type number format (using Format cell dialog) and enter some additional text in Type TextBox and press Enter key, the changes are not applied.


Steps to reproduce: 

1. Insert some time in a cell in spreadsheet (22:20)

2. Apply it a custom format that contains AM/PM (e.g. "h:mm AM/PM") and press Enter key

Observed: The AM/PM format is missing

Expected: AM or PM should be shown after the time


Workaround: Press OK button or first click somewhere else in order to change the focus

We should provide an easier API allowing the customers to remove the key bindings or change the commands that they trigger.

Workaround: There is attached a sample showing how all the commands triggered by the key bindings can be disabled.

Images inserted in RadSpreadsheet are resized when the active sheet is changed. The set size is very small, making them almost invisible.

Workaround: Remove the two RadNumericUpDowns in the Picture contextual tab in the ribbon UI. They can be recognized by their bindings, to SetShapeWidth.SelectedValue and SetShapeHeight.SelectedValue respectively.

Steps to reproduce:
- Open RadSpreadsheet with the default Ribbon UI present.
- Insert image using the button in the Ribbon -> Illustrations -> Pictures.
- Add new sheet using the Sheet Selector (+) button, or change the sheet to another sheet
- Return to the initial sheet.

Expected: The image retains its original size.
Actual: The image size is changed to very small one.

Add support for formats which can present numbers with non-arabic numerals, for example:
 
- Bengali - [$-bn-IN,500]0
- Devanagari - [$-hi-IN,400]0
- East Arabic - [$-ar-SA,200]0
- Persian - [$-ar-SA,300]0
- Gujarati - [$-gu-IN,700]0
- Kannada - [$-kn-IN,B00]0
- Khmer - [$-et-EE,1200]0
- Lao - [$-lo-LA,E00]0
- Malayalam - [$-ml-IN,C00]0
- Mongolian - [$-mn-MN,1300]0
- Burmese - [$-my-MM,1000]0
- Oriya - [$-or-IN,800]0
- Tamil - [$-ta-IN,900]0
- Telugu - [$-te-IN,A00]0
- Thai - [$-th-TH,D00]0
- Tibetan - [$-bo-CN,F00]0

Currently, the customers can bind data only to the Workbook property of RadSpreadsheet. Allow them binding cell range to a data source.

Add support for formats which can present numbers with non-arabic numerals, for example:
- Bengali - [$-bn-IN,500]0
- Devanagari - [$-hi-IN,400]0
- East Arabic - [$-ar-SA,200]0
- Persian - [$-ar-SA,300]0
- Gujarati - [$-gu-IN,700]0
- Kannada - [$-kn-IN,B00]0
- Khmer - [$-et-EE,1200]0
- Lao - [$-lo-LA,E00]0
- Malayalam - [$-ml-IN,C00]0
- Mongolian - [$-mn-MN,1300]0
- Burmese - [$-my-MM,1000]0
- Oriya - [$-or-IN,800]0
- Tamil - [$-ta-IN,900]0
- Telugu - [$-te-IN,A00]0
- Thai - [$-th-TH,D00]0
- Tibetan - [$-bo-CN,F00]0