Accessing a Namespace Programmatically

It is worth reiterating that a namespace is nothing more than a convenient way for us mere humans to logically understand and organize related types. Consider again the System namespace. From your perspective, you can assume that System.Console represents a class named Console that is contained within a namespace called System. However, in the eyes of the .NET runtime, this is not so. The runtime engine sees only a single class named System.Console.

In C#, the using keyword simplifies the process of referencing types defined in a particular namespace. Here is how it works. Let’s say you are interested in building a graphical desktop application using the WPF API. While learning the types each namespace contains takes study and experimentation, here are some possible candidates to reference in your program:

// Here are some possible namespaces used to build a WPF application.

using System; // General base class
library types.
using System.Windows.Shapes; // Graphical rendering types.
using System.Windows.Controls; // Windows Forms GUI widget types.
using System.Data; // General datacentric
types.
using System.Data.SqlClient; // MS SQL Server dataaccess types.

Once you have specified some number of namespaces (and set a reference to the assemblies that define them), you are free to create instances of the types they contain. For example, if you are interested in creating an instance of the Button class (defined in the System.Windows.Controls namespace), you can write the following:

// Explicitly list the namespaces used by this file.
using System;

using System.Windows.Controls;

class MyGUIBuilder
{
public void BuildUI()
 {
// Create a button control.
Button btnOK = new Button();
...
 }

}

Because your code file is importing the System.Windows.Controls namespace, the compiler is able to resolve the Button class as a member of this namespace. If you did not import the System.Windows.Controls namespace, you would be issued a compiler error. However, you are free to declare variables using a fully qualified name as well.

// Not listing System.Windows.Controls namespace!
using System;
class MyGUIBuilder
{
 public void BuildUI()
 {
  // Using fully qualified name.
  System.Windows.Controls.Button btnOK =
  new System.Windows.Controls.Button();
  ...
 }

}

While defining a type using the fully qualified name provides greater readability, I think you’d agree that the C# using keyword reduces keystrokes. In this text, I will avoid the use of fully qualified names (unless there is a definite ambiguity to be resolved) and opt for the simplified approach of the C# using keyword.

However, always remember that the using keyword is simply a shorthand notation for specifying a type’s fully qualified name, and either approach results in the same underlying CIL (given that CIL code always uses fully qualified names) and has no effect on performance or the size of the assembly.

 End Of This Post

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