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Lab 3.1: Creating a .NET Framework Component

Topic Objective

To introduce the lab.

Lead-in

In this lab, you will learn how to create a simple

.NET Framework component in C#.

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Exercise 1

Creating a Component in C#

In this exercise, you will use C# to create a component that provides a wrapper for a private array of strings. The wrapper includes a read-only Count property, which returns the number of strings in the array, and a public GetString method, which takes an integer argument and returns the string in the private array at that index. The GetString method will also implement structured exception handling to ensure that the argument of the index is within range of the array.

!Specify namespace information and class declarations

1.Open Notepad and reference the System namespace.

2.Create a new namespace named CompCS. CompCS will contain the class for your component.

! Create the class implementation

1.Create a public class named StringComponent.

2.Declare a private field named StringSet of type array of string elements.

3.Create a public default constructor.

The default constructor takes no arguments.

4.Assign to the field StringSet an array of strings initialized with the following four strings:

"C# String 0",

"C# String 1",

"C# String 2",

"C# String 3"

5.Create the public GetString method, which takes an integer as an argument. That integer must be a valid index for the StringSet array.

a.If the integer is an invalid index, throw an index out of range exception.

b.If the integer is a valid index, return the StringSet string at that index.

6.Create a read-only Count property that gets the number of string elements in the StringSet array.

7.Save the file as CompCS.cs in the <install folder>\Labs\Lab03.1 folder.

" Creating a Simple Console Client

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In this section, you will learn how to write a simple console application that calls the .NET Framework runtime-compatible component that was created in the previous section.

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This topic explains how to reference types in your applications by using namespaces and how to use a namespace alias if you need to remove ambiguity to type references.

Using the Namespaces

By using the namespaces in the program, you can reference types in the library without fully qualifying the type name.

To use the component namespaces in C#, you must enter a using statement followed by the name of the component namespaces:

using CompCS; using CompVB;

Using an Alias

Consider a scenario where similar C# and Microsoft Visual Basic® components use the same type name (StringComponent). You must still fully qualify the type name to remove any ambiguity when referring to the GetString method and the Count property. In C#, you can create and use aliases to solve this problem.

The following C# example shows how to alias the component namespaces so that you do not have to fully qualify the type names:

using CSStringComp = CompCS.StringComponent; using VBStringComp = CompVB.StringComponent;

Instantiating the Component

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To instantiate the StringComponent class, you declare a local variable of type StringComponent and create a new instance of StringComponent, as in the following example:

//…

using CSStringComp = CompCS.StringComponent;

class MainApp

{

public static void Main() {

CSStringComp myCSStringComp = new CSStringComp(); //…

}

}

Calling the Component

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After instantiating the StringComponent class, the client can iterate over the string array in the component and return the appropriate output, as in the following example:

using System;

using CSStringComp = CompCS.StringComponent;

class MainApp

{

public static void Main() {

CSStringComp myCSStringComp = new CSStringComp(); // Display result strings from CS component

Console.WriteLine("Strings from CS StringComponent"); for (int index = 0; index < myCSStringComp.Count; index++) {

Console.WriteLine(myCSStringComp.GetString(index));

}

}

}

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To build the client, you can compile the source code from a command prompt window. You must use the /reference option to reference all of the assemblies that contain the StringComponent class, as in the following example:

csc /reference:CompCS.dll,CompVB.dll!

/out:ClientCS.exe ClientCS.cs

Running a client program that first iterates over the C# component’s strings and then iterates over the Visual Basic component’s strings will produce the following output:

Strings from C# StringComponent

C# String 0

C# String 1

C# String 2

C# String 3

Strings from VB StringComponent

VB String 0

VB String 1

VB String 2

VB String 3

Exercise 1

Creating a Client Application in C#

In this exercise, you will create a simple console application to call the C# component that you created in Lab 3.1, “Creating a .NET Framework Component,” and a Visual Basic component that is already provided. The Visual Basic component provides the same StringComponent class as the C# component.

!Specify namespace information

1.Open Notepad and import the System namespace.

2.Use the namespace of the C# component that you created in Lab 3.1, “Creating a .NET Framework Component.”

3.Use the namespace of the Visual Basic component. The namespace of the Visual Basic component is CompVB.

Because you are importing two libraries that contain the same type name but have different namespaces, use an alias directive to allow for unambiguous references to StringComponent classes.

4.Create a class in C# called MainApp.

5.Specify the program entry point.

The entry point takes no arguments and does not return a value.

!Write the code to call the C# and Visual Basic components

1.Assign to a local variable named myCSStringComp a new instance of the C# version of StringComponent.

2.Write the code to print the following string to the console:

Strings from C# StringComponent

3.Iterate over all of the members of the C# string component and output the strings to the console.

4.Repeat steps 1 through 3 for the Visual Basic version of StringComponent. Name the local variable myVBStringComp.

5.Save the file as ClientCS.cs in the <install folder>\Labs\Lab03.2 folder.