Archive for the ‘.Net 3.0’ Category

Invalid postback or callback argument – AJAX Control Toolkit

I was working to add some Ajax interactivity to a page that needed some asynchronous workings. Unfortunately, after displaying a ModalPopupExtender and the user clicking the Close button on the “popup”, the page would throw the following exception:

System.ArgumentException occurred
  Message=”Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation=\”true\”/> in configuration or <%@ Page EnableEventValidation=\”true\” %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.”
       at System.Web.UI.ClientScriptManager.ValidateEvent(String uniqueId, String argument)

There are lots of explanations out there for this kind of problem, but none of the common answers really fit. The most common answer was to disable event validation. That wasn’t a good answer for me, I don’t think disabling an important security feature because you have complex code is a good solution. The other common answer was to override the render event to register the control posting back with the ScriptManager. This did not work at all for me.

After finding an reading through this post and the comments, I realized the problem was indeed in the code. After the call to ModalPopupExtender.Show(), the original code was re-binding a grid on the page. This order of events was causing the problem. I changed the binding to occur before the call to the ModalPopupExtender by changing which event containing the rebinding call, and the error went away.

eBooks on CodePlex

Wriju has a gread roundup of eBooks/guidance available on CodePlex.

Building a Basic Excel Document with Open XML

I recently gave a talk about Open XML, and found that there were not many complete code samples out there which described how to build Office 2007 documents using .Net and SpreadsheetML. Most of the examples I ran into were snippets or functions, or just examples of the SpreadsheetML. As one of my demos, I created a C# class which builds a basic spreadsheet. This post describes that class.

There are prerequisite installs required to run this code:

  • .Net 3.0 Framework (System.IO.Packaging is part of WPF)
  • SDK for Open XML Formats, which is currently a CTP, so the code is subject to change if the object model changes at all with the final release (so therefore does the code in this post).
  • Code Snippets that are available for Open XML.

The class (called Spreadsheet) does two basic things:

  1. Create a spreadsheet package
  2. Insert data into a worksheet in the newly created package

The first step is creating the package, which consists of XML files for the SpreadsheetML and XML files which manage the relationships between those files. In an Open XML spreadsheet, the minimal spreadsheet package requires three documents containing SpreadsheetML:

  1. A workbook file
  2. A worksheet file
  3. A relationship file

Additionally, SpreadsheetML uses a concept called “Shared Strings”. SpreadsheetML dictates storing Shared Strings separately from the worksheet in their own document, so the document stores less data if the document re-uses strings. Strings can also be added to the spreadsheet “in-line” and not used Shared Strings storage. For this example labels are stored as Shared Strings to demonstrate the concept, therefore the spreadsheet package also requires a Shared Strings document.

The SDK for Open XML Formats provides a new component, Microsoft.Office.DocumentFormat.OpenXml.dll, that wraps some of the functionality of creating an Open XML document with System.IO.Packaging. Essentially it manages creating the files and the relationships between the files in the package. Once you have created the files and relationships, you still need to create code to insert actual data into the documents. This example uses two steps:

  1. Create the basic XML document using a template of existing XML
  2. Insert data into the existing XML.

The following are the contents of three small XML files created and added to a Templates directory in the solution. These three files are the basis for the required parts of the package:

The workbook template

<?xml version=1.0 encoding=UTF-8 standalone=yes?>

<workbook xmlns= xmlns:r=>


        <sheet name={1} sheetId=1 r:id={0} />



Notice that the XML contains .Net placeholders. Later on we can replace these with actual values that can vary at run time.

The worksheet template

<?xml version=1.0 encoding=UTF-8 standalone=yes?>

<worksheet xmlns= >



The shared strings template

<?xml version=1.0 encoding=UTF-8 standalone=yes?>

<sst xmlns=>


These XML templates make up the basic content of the package. The C# class contains a CreateSpreadSheet procedure which will create the basic pieces of the package. The main thing to notice is that  by creating the part object (workbook, shared strings, worksheet), you are only creating the part file, not the content of that part file. The templates above become the content for the parts. There is no need to manage the relationship files directly, the API is doing that automatically.

public void CreateSpreadsheet(string path, string firstSheetName)


    using (SpreadsheetDocument doc = SpreadsheetDocument.Create(path, SpreadsheetDocumentType.Workbook))


        //Add the workbook

        WorkbookPart workbook = doc.AddWorkbookPart();


        //Create the shared strings part

        SharedStringTablePart stringTable = workbook.AddNewPart<SharedStringTablePart>();

        this.AddPartXml(stringTable, this.ReadXML(@”Templates\SharedStringTemplate.xml”));


        //Create a worksheet

        WorksheetPart sheet = workbook.AddNewPart<WorksheetPart>();


        //Get the relationship id so the workbook and worksheet can be related

        string sheetId = workbook.GetIdOfPart(sheet);


        this.AddPartXml(workbook, this.WorkbookXml(sheetId, firstSheetName));

        this.AddPartXml(sheet, this.ReadXML(@”Templates\WorkSheetTemplate.xml”));





The only interesting part is retrieving the ID of the worksheet part when building the workbook part. To create the content of each part the procedure opens an XML file and streams the content into the file. There are helper functions for this, which are really just standard ways of handling XML in .Net:

protected void AddPartXml(OpenXmlPart part, string xml)


    using (Stream stream = part.GetStream())


        byte[] buffer = (new UTF8Encoding()).GetBytes(xml);

        stream.Write(buffer, 0, buffer.Length);




protected string ReadXML(string fileName)


    StreamReader reader = new StreamReader(Environment.CurrentDirectory + @”\” + fileName);

    string contents = reader.ReadToEnd();


    return contents;



protected string WorkbookXml(string sheetId, string sheetName)


    string contents = this.ReadXML(@”Templates\WorkbookTemplate.xml”);


    return string.Format(contents, sheetId, sheetName);


Notice the WorkbookXml procedure has a call to string.Format to replace some placeholders with actual data: the ID of the worksheet part relationship and the name of the worksheet. The name of the worksheet is important later, when we want to add data to the worksheet.

The second step is to actually add data to the worksheet. The class uses two functions available as Code Snippets (XLInsertStringIntoCell, and XLInsertNumberIntoCell). I won’t reproduce the code here as I don’t own it, but essentially the functions open the proper parts and insert the data. These functions take in the file, the sheet name, cell reference and cell value as parameters.

Lastly, I wrote a console app to exercise the Spreadsheet class:

class Program


    protected static readonly string fileName = “example.xlsx”;

    protected static readonly string firstSheetName = “Sheet1”;


    static void Main(string[] args)


        string path = Environment.CurrentDirectory + @”\” + fileName;


        Spreadsheet file = new Spreadsheet();


        file.CreateSpreadsheet(path, firstSheetName);


        file.XLInsertStringIntoCell(fileName, firstSheetName, “A1”, “Category”);

        file.XLInsertStringIntoCell(fileName, firstSheetName, “B1”, “Value”);

        file.XLInsertStringIntoCell(fileName, firstSheetName, “A2”, “Red”);

        file.XLInsertNumberIntoCell(fileName, firstSheetName, “B2”, 30);

        file.XLInsertStringIntoCell(fileName, firstSheetName, “A3”, “Blue”);

        file.XLInsertNumberIntoCell(fileName, firstSheetName, “B3”, 60);

        file.XLInsertStringIntoCell(fileName, firstSheetName, “A4”, “Green”);

        file.XLInsertNumberIntoCell(fileName, firstSheetName, “B4”, 10);


        Console.WriteLine(“Workbook created at “ + path);





Before the comments start to fly, I want to point out a couple things:

  • This bit of code is not that efficient, I realize it opens and closes the package a bunch of times. This is really just to demonstrate what is possible and not what is necessarily the best practice. There are very few code samples available, and I am shooting for simplicity here.
  • I know ExcelPackage is on CodePlex and does a better job of wrapping the APIs involved and is much easier to write code with. Once you have a basic understanding of these APIs you will appreciate for the work being done on that project.

Download the VS 2005 project. Don’t forget to install all the prerequisites listed above before trying the project. I didn’t include the two functions necessary from the Code Snippets in the project either (since I didn’t write that code), you will have to put those in yourself.

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Speaking at West Michigan Dot Net User Group – WCF

I will be speaking on July 17th on Windows Communication Foundation. See the West Michigan .NET Users Group site for details.

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Even More WCF Links

Articles by Juval Lowy

Aaron Skonnard’s Wiki

WCF Developer Center on MSDN

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WCF Link List

Architecture Overview

MSDN Forum

WCF Tools

Contract Versioning


Integrating WWF and WCF

WCF Developer Home

WCF Team Blog

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