Uncategorized

New beta Microsoft certification exams available free between March 31, 2010 and April 20, 2010.

• 70-515 TS: Web Applications Development with Microsoft® .NET Framework 4
• 70-516 TS: Accessing Data with Microsoft® .NET Framework 4
• 70-513 TS: Windows Communication Foundation Development with Microsoft® .NET Framework 4
• 70-519 Pro: Designing and Developing Web Applications using Microsoft® .NET Framework 4

More info on Gerry O’Brien’s blog here: Free Certification Exams

Neil spotted this quirky behaviour in the TableHeaderCell control. Suppose you’ve got a Table web control that renders a <table> tag with a <th scope=”col”>, using code something like this:

Table table = new Table()
{
    Rows =
    {
        new TableRow()
        {
            Cells =
            {
                new TableHeaderCell()
                    { Scope = TableHeaderScope.Column, Text = "MyColumn" }
            }
        }
    }
};

Then the rendered HTML won’t be W3C compliant because a scope value of “column” isn’t valid:

<table border="0">
    <tr>
        <th scope="column"></th>
    </tr>
</table>

According to the W3C HTML and XHTML specs, the acceptable values for scope are [row|col|rowgroup|colgroup]. This is confirmed by the W3C Markup Validation Service, which reports the error:

Stepping into the source code for the TableHeaderCell control with Reflector or the .NET Reference Source, you can see the root of the problem:

protected override void AddAttributesToRender(HtmlTextWriter writer)
{
    TableHeaderScope scope = Scope;

    if (scope != TableHeaderScope.NotSet)
    {
        writer.AddAttribute(HtmlTextWriterAttribute.Scope,
            scope.ToString().ToLowerInvariant());
    }
}

When the control sets the scope attribute’s value, it uses a lowercase string representation of the TableHeaderScope.Column enumeration, i.e. “column”. An enum value of TableHeaderScope.Col would’ve been ok, but TableHeaderScope.Column is invalid.

Workarounds

Neil has a good workaround by adding the scope attribute manually instead of using the TableHeaderCell.Scope property:

TableHeaderCell th = new TableHeaderCell();
th.Attributes["scope"] = "col";

I thought I’d have a go at extending this fix into a simple control adatper that makes sure TableHeaderCell always renders itself correctly. It works by checking whether the Scope property is set to TableHeaderScope.Column, and if so manually adds the attribute scope=”col” instead. Here’s the code:

    public class TableHeaderCellAdapter : WebControlAdapter
    {
        protected override void RenderBeginTag(HtmlTextWriter writer)
        {
            TableHeaderCell th = (TableHeaderCell) this.Control;

            if (th.Scope == TableHeaderScope.Column)
            {
                th.Scope = TableHeaderScope.NotSet;
                th.Attributes["scope"] = "col";
            }

            base.RenderBeginTag(writer);
        }
    }

To associate the control adapter class with the TableHeaderCell control, add a browser definition file to the App_Browsers folder:

    <!-- file: ~/App_Browsers/ControlAdapters.browser -->
    <browsers>
        <browser refID="Default">
            <controlAdapters>
                <adapter
                  controlType="System.Web.UI.WebControls.TableHeaderCell"
                  adapterType="TableHeaderCellAdapter" />
            </controlAdapters>
        </browser>
    </browsers>

As part of Microsoft’s ongoing Trustworthy Computing initiative, Vista takes the secure by default principle more seriously than previous versions of Windows. Consequently, many features aren’t installed by default, one of which is IIS 7. So, to install IIS go to:

Control Panel – Programs – Turn Windows features on or off

Then find the Intenet Information Services section and add everything you need, including ASP.NET.

Check out Stuart Cam’s excellent comparison of agile versus waterfall development models, illustrated as drawing a horse:

That freakish Frankenstein waterfall horse is going to give me nightmares.

Microsoft’s just added eight hours of .NET 4.0 and Visual Studio 2010 sessions to its training site msdev.com with New Features in .NET Framework 4 and Visual Studio 2010, Beta 2.

Subjects covered are:

• Parallelism
• ADO.NET Data Services
• F#
• Office Programmability
• ASP.NET AJAX
• ASP.NET MVC
• ASP.NET WebForms
• Managed Languages

And there’s even more ASP.NET 4.0 training in the ASP.NET 4.0 Quick Hit Videos series.  A great introduction to loads of new features in bite-size pieces:

• Chart Control
• Dynamic Metadata
• Permanent Redirect
• Imperative WebForms Routing
• Declarative WebForms Routing
• Outbound WebForms Routing
• Auto Start
• Clean Web.Config Files
• Predictable Client IDs
• Selective View State
• The HtmlEncoder Utility Method
• New Rendering Option for Check Box Lists and Radio Button Lists
• Persistent GridView Row Selection
• Table Free Templated Controls
• Easy State Compression
• Tableless Menu Control
• Imperative JavaScript Syntax for Microsoft Client Side Controls
• The ScriptLoader
• jQuery Syntax for Microsoft Ajax
• AJAX Data Templates
• Hidden Field Divs
• Disabled Control Styling

ASP.NET 2.0 has some great localization features that make it easy to build multilingual web applications. The problem comes when you need different business logic for different countries, maybe to validate a local address or calculate shipping costs. You somehow need to get the application to behave differently based on a country code or the thread’s current culture setting.

For simple variations you can use separate configuration settings for each country. For example, a regular expression in web.config to validate a local telephone number. But if the logic is more complex then you might need a different plan.

An obvious approach is to use conditional switch/select-case statements, like this:

switch (countryCode)
{
   case "FR":
   /* Logic for France */
   case "US":
   /* Logic for USA */
}

But for large applications this can quickly get unwieldy and difficult to manage. Adding a new country means finding every switch statement and adding a new case.

Instead, a good solution is the Factory Method design pattern. It makes your application much easier to maintain, and adding new countries is easy. Here’s a quick example that extends the idea of validating local postcode formats.

Class Diagram

These are the classes used, described below in more detail.

Step 1

Create an abstract class for performing local validation called LocalValidatorBase. This is a base class which can’t be instantiated. Add a method signature IsValidPostcode that takes a string and returns a boolean. Classes for various countries can now derive from LocalValidatorBase and override IsValidPoscode with custom validation logic.

(The LocalValidatorBase class can contain logic to share between all the subclasses, but if this isn’t necessary then you can create an interface instead of an abstract class called something like ILocalValidator.)

Step 2

Derive two local validation classes from LocalValidationBase called LocalValidatorAU and LocalValidatorDE, one for Australia and one for Germany. In each, override IsValidPoscode to perform country-specific logic for validating a postcode, maybe by checking the string length or matching against a regular expression. The details aren’t important here.

Step 3

Create a factory class to return the correct validator object for the current country setting. Add a static/shared factory method called GetLocalValidator that returns a LocalValidatorBase class. The magic of polymorphism means this method can return any class derived from LocalValidatorBase. Use a switch statement, or some other conditional logic, to return a new instance of LocalValidatorDE or LocalValidatorAU depending on a country code parameter or the thread’s current culture name.

Step 4

That’s all there is to it. You can now call the factory method to get the correct validator object for the current country.

' call the factory method to get a concrete validator
Dim validator As LocalValidatorBase = _
  LocalValidatorFactory.GetLocalValidator()

Dim isValid As Boolean = validator.IsValidPostcode("12345")

The validation success depends on the rules in the object returned by GetLocalValidator, which will be different depending on the current country.

Firebug, a developer plug-in for Firefox, just made front-end development a lot easier:

• Inspect and edit live HTML and CSS
• Visualise CSS box-model
• Monitor network metrics
• Debug and profile JavaScript
• DOM explorer

Here are a few online resources for studying towards MCTS: .NET Framework 2.0 Web Applications:

Exam 70–528: .NET 2.0 Web-Based Client Development

• Microsoft Preparation Guide
• Web-based Client Development – Free Skills Assessment
• MeasureUp practice test (150 questions)
• Wikibook MCTS textbook

Exam 70–536: .NET 2.0 Application Development Foundation

• Microsoft Preparation Guide
• MeasureUp practice test (150 questions)
• MCTS 70-536 Exam Prep (book)
• Exam syllabus with MSDN links
• C# Online.NET Study Guide