Developer .NET UPDATE--Visual Studio 2005's Partial Classes--August 20, 2004

Visual Studio 2005 Offers Partial Classes

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Featured Thread: Why Doesn't the CLR's CTS Define Syntax?

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Toolkit Reads, Writes, and Converts Images

1. Developer .NET Perspectives

Visual Studio 2005 Offers Partial Classes

In my last column "Anonymous Admirer" (http://www.winnetmag.com/windows/article/articleid/43549/43549.html), I introduced you to some new language-related features in Visual Studio 2005 beta 1. In this column, I want to focus on how the Windows .NET Framework is changing under the covers. Because of these infrastructure changes, Visual Basic .NET and C# support partial classes, which in turn, provides you with a richer development experience in Visual Studio 2005.

In Visual Studio 2005, you can split the implementation of a specific class across multiple source files. A good comparison for this split is the way in which C++ splits the implementation of a class across two files: .h and .cpp. The header, or .h, file is generally associated with the declaration of the methods and properties used by the class, whereas the .cpp file is generally associated with the class's source code.

In Visual Studio 2005, you use the Partial keyword in a class declaration to tell the compiler that the class implementation code has been split across several source files. The code is then combined during the compilation process.

The best way to witness the effects of partial classes is to create a new Windows Form-based application in both Visual Studio 2005 and Visual Studio .NET 2003. Then, on each form, drop a single control, such as a button. If you open the code view of the Windows Form in Visual Studio .NET 2003, you'll notice all the stock code to implement this button at the top of the source file. Trying to navigate through all that generated code with custom event handlers can be a pain. But if you open the code view of the Windows Form in Visual Studio 2005, all you'll find is a simple declaration along the lines of Public Class Form1 End Class Gone is the stock code that clutters up the source files of classes in Visual Studio .NET 2003.

To find the form's generated logic in Visual Studio 2005, you need to look elsewhere because of the use of partial classes. Open Solution Explorer, which shows you the default view of the objects that make up your projects. One of Solution Explorer's options is to "Show All Files." This option lets you see not only the top-level elements in your project but also every file that exists in your project. When you select this option, you'll find two new files underneath the form's source file. If you open the file that has a name similar to Form1.Designer.vb, you'll find all the stock code. At the top of the class code is the partial keyword, which tells the compiler that this code is a partial implementation of a class.

The partial keyword, however, doesn't need to be included with every source file for a class; one file can be declared without this keyword. However, I think this practice is a bad idea. I believe the keyword should be required in every file that's part of a partial class because this keyword would let you know that there's additional source code associated with a class. In a maintenance scenario in which you're searching for a bug, you might not immediately realize that a class has more than one source file.

As I mentioned previously, when you select the "Show All Files" option, Solution Explorer displays two new files underneath the source file. Besides Form1.Designer.vb, you'll find a resource file. Each Windows Form now comes with a unique resource file to which you can add graphics, audio bites, and strings that you want to associate with that form. Just like the partial keyword, the resource file provides a way for you to automatically partition the elements in your Windows Form source code. In my next column, I'll show you how this same idea of presenting a project as a collection of small units is changing ASP.NET.

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Featured Thread: Why Doesn't the CLR's CTS Define Syntax?

Novice forum member savanted1 is wondering why the Common Type System (CTS) in the Windows .NET Framework's Common Language Runtime (CLR) defines only semantics and not both syntax and semantics. If you know why, go to the following URL:

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