Lesson 07: Namespaces

Fundamentals of Namespaces

Introduction

A namespace is a section of code that is identified with a specific name. The name could be anything such as somebody's name, the name of the company's department, a city, etc.

Practical Learning: Introducing Namespaces

Start Microsoft Visual Studio
Create a new ASP.NET Core Web App named PieceWork3
Uncheck the Configure For HTTPS check box
To create a new class, in the Solution Explorer, right-click Pages -> Add -> New Item...
In the middle list of the Add New Item dialog box, click Code File (don't click Class)
Change the Name to Driver
Click Add

In the empty document, type the following:

public class Driver
{
    public string first_name;
    public string last_name;
}

To create a new file, on the main menu, click Project -> Add New Item...
In the middle list, make sure Code File is selected.
Change the Name to Truck
Click Add

In the empty document, type the following:

/* Piecework is the type of work that is paid on the number 
 * of items produced, the distance driven, etc.
 * In this exercise, a business uses trucks driven by some 
 * employees or contractors to deliver some products. 
 * The drivers are paid based on the distance they travel to 
 * deliver one or many products. */
public class Truck
{
    public string make;
    public string model;
}

To start a new razor page, in the Solution Explorer, right-click Project -> Add -> Razor Page...
In the middle list of the Add New Scaffolded Item dialog box, make sure Razor Page - Empty is selected (if not, click it).
Click Add
Change the Name to PieceDelivery
Click Add

Change the document as follows:

@page
@model PieceWork1.Pages.PieceDeliveryModel
@{
    int miles;
    double pieceworkRate;

    Truck trk = new Truck();
    Driver drv = new Driver();

    drv.first_name = "Robert";
    drv.last_name = "Crawford";
    trk.make = "Chevrolet ";
    trk.model = "3500 Express 4x2";
    miles = 396;
    pieceworkRate = 0.58;

    double pay = miles * pieceworkRate;
    string strPay = $"{pay:F}";
}

<h3 style="text-align: center"> - Piece Work Delivery -</h3>

<hr />

<table width="350" align="center">
    <tr>
        <td width="125">Driver:</td>
        <td>@drv.first_name @drv.last_name</td>
    </tr>
    <tr>
        <td>Truck Details:</td>
        <td>@trk.make @trk.model</td>
    </tr>
</table>

<hr />

<table align="center" width="350">
    <tr>
        <td width="125">Miles Driven:</td>
        <td>@miles</td>
    </tr>
    <tr>
        <td>Piecework Rate:</td>
        <td>@pieceworkRate</td>
    </tr>
    <tr>
        <td>Gross Salary:</td>
        <td>@strPay</td>
    </tr>
</table>

To execute, on the main menu of Microsoft Visual Studio, click Debug -> Start Without Debugging

In the browser, click the right side of the address, type /PieceDelivery and press Enter:

 - Piece Work Delivery -
Driver: 	Robert Crawford
Truck Details: 	Chevrolet 3500 Express 4x2
Miles Driven: 	396
Piecework Rate: 0.58
Gross Salary: 	229.68

Return to your programming environment

Manually Creating a Namespace

To create a namespace:

Use a keyword code named namespace. Follow it by a named section
Right-click the section where you want to create the namespace and double-click Insert Snippet... Double-click Visual C#. In the list, double-click namespace

Like a class, the section that is part of a namespace starts with an opening curly bracket "{" and ends with a closing curly bracket "}". Here is an example:

namespace Business
{
}

Between the curly brackets, you can type anything that is part of the namespace. For example, you can create a class inside a namespace. Here is an example:

namespace Business
{
    class House
    {
    }
}

Practical Learning: Creating a Namespace

Click the Truck.cs tab to access its class

To create a namespace, change the document as follows:

namespace BusinessInventory
{
    /* Piecework is the type of work that is paid on the number 
     * of items produced, the distance driven, etc.
     * In this exercise, a business uses trucks driven by some 
     * employees or contractors to deliver some products. 
     * The drivers are paid based on the distance they travel to 
     * deliver one or many products. */
    public class Truck
    {
        public string make;
        public string model;
    }
}

Click the Driver.cs tab to access its class and change its document as follows:

namespace HumanResources
{
    public class Driver
    {
        public string first_name;
        public string last_name;
    }
}

Click the PieceDelivery.cshtml tab to access the file

Accessing the Members of a Namespace

After creating the necessary members of a namespace, you can use the period operator to access an item that is a member of the namespace. To do this, in the desired location, type the name of the namespace, followed by a period, followed by the desired member of the namespace. Here is an example:

// This class is created in a Code File
namespace Business
{
    class House
    {
        public string propNumber;
        public double marketValue;
    }
}

// This section is from a webpage
@page
@model Valuable.Pages.FoundationsModel
@{
    Business.House property = new Business.House();
    
    prop.propNumber = "D294FF";
    prop.marketValue = 425_880;
}

<pre>=//= Altair Realtors =//=
    Properties Inventory
Property #: @prop.propNumber
Market Value:  @prop.marketValue</pre>

This would produce:

=//= Altair Realtors =//=
    Properties Inventory
Property #: D294FF
Market Value:  425880

Practical Learning: Accessing a Member of a Namespace

Change the PieceDelivery.cs document as follows:

@page
@model PieceWork1.Pages.PieceDeliveryModel
@{
    int miles;
    double pieceworkRate;

    BusinessInventory.Truck trk = new BusinessInventory.Truck();
    HumanResources.Driver drv = new HumanResources.Driver();

    drv.first_name = "Joseph";
    drv.last_name = "Garrett";
    trk.make = "Ram";
    trk.model = "5500 Regular Cab DRW 4x4, Duramag Dry Freight";
    miles = 672;
    pieceworkRate = 0.36;

    double pay = miles * pieceworkRate;
    string strPay = $"{pay:F}";
}

<h3 style="text-align: center"> - Piece Work Delivery -</h3>

<hr />

<table width="350" align="center">
    <tr>
        <td width="125">Driver:</td>
        <td>@drv.first_name @drv.last_name</td>
    </tr>
    <tr>
        <td>Truck Details:</td>
        <td>@trk.make @trk.model</td>
    </tr>
</table>

<hr />

<table align="center" width="350">
    <tr>
        <td width="125">Miles Driven:</td>
        <td>@miles</td>
    </tr>
    <tr>
        <td>Piecework Rate:</td>
        <td>@pieceworkRate</td>
    </tr>
    <tr>
        <td>Gross Salary:</td>
        <td>@strPay</td>
    </tr>
</table>

To execute the project to make sure it is working, on the main menu of Microsoft Visual Studio, click Debug -> Start Without Debugging:

 - Piece Work Delivery -
Driver: 	Joseph Garrett
Truck Details: 	Ram 5500 Regular Cab DRW 4x4, Duramag Dry Freight
Miles Driven: 	672
Piecework Rate: 	0.36
Gross Salary: 	241.92

Return to your programming environment

New Convention:

From now on, in our lessons, when we write namespace-name.layout-name, we mean the layout-name, such as a class, that was created in, or is a member of, the indicated namespace-name.

Managing Namespaces

Inserting a Namespace

If you have existing code already, you can include it in a namespace. To do that:

Click above the section of code, type namespace followed by a name and {. Locate the end of the section and type }
Select the code that you want to include in a namespace. Right-click the selection, position the mouse on Snippet, and click Surround With... In the list, double-click namespace

Renaming a Namespace

You can manually rename a namespace or benefit from the assistance of the Code Editor. To rename a namespace:

In the Code Editor, locate its name and change it. Then click the arrow of its smart tag and choose an option from the menu
Right-click the name and click Rename... Then follow the dialog boxes

Using a Namespace in a Code File

We saw that, to access a class that is a member of a namespace, you must "qualify" the class using the period operator. Instead of using this approach, if you already know the name of a namespace that exists or the namespace has been created in another file, you can use a special keyword to indicate that you are using a namespace that is defined somewhere. This is done with a keyword named using. To do this, on top of the file (preferably), type using followed by the name of the namespace.

With the using keyword, you can include as many external namespaces as necessary.

Whether you use the using keyword or not, you can still access a member of a namespace by fully qualifying its name. In fact, when there is a name conflict, even if you use the using keyword, you must still qualify the name of the class.

Using a Namespace in a Razor Page

you can reference a namespace in a razor page. The formula is almost the same as when referencing a namespace in a code file. In a razor page, precede the using keyword with the @ symbol and don't end the statement with a semicolon.

Practical Learning: Using Namespaces

To use the using keyword, change the PieceDelivery.cshtml document as follows:

@page
@model PieceWork1.Pages.PieceDeliveryModel
@using BusinessInventory
@using HumanResources
@{
    int miles;
    double pieceworkRate;

    Truck trk = new Truck();
    Driver drv = new Driver();

    drv.first_name = "Jennifer";
    drv.last_name = "Foster";
    trk.make = "Ford";
    trk.model = "E-350 4x2 Rockport Cutaway Van";
    miles = 409;
    pieceworkRate = 0.48;

    double pay = miles * pieceworkRate;
    string strPay = $"{pay:F}";
}

<h3 style="text-align: center"> - Piece Work Delivery -</h3>

<hr />

<table width="350" align="center">
    <tr>
        <td width="125">Driver:</td>
        <td>@drv.first_name @drv.last_name</td>
    </tr>
    <tr>
        <td>Truck Details:</td>
        <td>@trk.make @trk.model</td>
    </tr>
</table>

<hr />

<table align="center" width="350">
    <tr>
        <td width="125">Miles Driven:</td>
        <td>@miles</td>
    </tr>
    <tr>
        <td>Piecework Rate:</td>
        <td>@pieceworkRate</td>
    </tr>
    <tr>
        <td>Gross Salary:</td>
        <td>@strPay</td>
    </tr>
</table>

To execute the project to make sure no error was introduced, on the main menu of Microsoft Visual Studio, click Debug -> Start Without Debugging:

 - Piece Work Delivery -
Driver: 	Jennifer Foster
Truck Details: 	Ford E-350 4x2 Rockport Cutaway Van
Miles Driven: 	409
Piecework Rate: 0.48
Gross Salary: 	196.32

Return to your programming environment

Removing a Namespace

As mentioned above, in the top section of a document, you can create a list of namespaces you are interested to use. Here is an example:

using Accounting;
using HumanResources;
using ResearchAndDevelopment;

public class Exercise
{
}

After making the list of the desired namespaces, you can access their members in your code. Sometimes, you will have added some namespace but not access their members. When that happens, you can remove those namespaces from the top list in the document. You can do that manually. As an alternative, you can right-click anywhere inside the document and click Remove and Sort Usings.

Namespaces from a Project

Introduction

If you create an ASP.NET Core Web project in Microsoft Visual Studio, the studio creates some namespaces and adds classes to those namespaces. The studio uses the name of the project for the namespace.

A Namespace from a Class

In Microsoft Visual Studio, to create a new class:

On the main menu, you can click Project -> Add Class...
In the Solution Explorer, right-click Pages -> Add -> click Class...

In the middle list of the Add New Item dialog box, make sure Class is selected. Accept or change the Name of the class. Click Add. If you use any of these approaches, Microsoft Visual Studio would create a namespace using the name of the project and would add the new class to it.

A Models Namespace

When you work in an ASP.NET environment (Core, MVC, etc), it is recommended that you create you classes in a folder named Models. If you create an MVC application in Microsoft Visual Studio, the studio would automatically reate a Models folder for you. If you are creating an ASP.NET Core Web application, that folder is not automatically created for you: You must manually create it.

To manually create a Models folder in an ASP.NET Core Web application, in the Solution Explorer, right-click the name of the project, position the mouse on Add, and click New Folder. Then type Models as the name of the folder. You can then create a class in the Models folder. To do this, in the Solution Explorer, right-click Models, position the mouse on Add, and click Class... Give a name to the class and click Add.

When you create a folder named Models, Microsoft Visual Studio creates a namespace that is a combination of the name of the project, a period, and Models. Whenever you add a class to the Models folder, the class is created and put in the Models namespace. Whenever you need to reference that class, if you are working in a regular code file, in the top section of the file, you can type using followed by the whole namespace. If you are working in a razor page, in the top section of the file, after the @page and the @model... lines, type @using followed by the namespace.

Creating and Using Many Namespaces

Introduction

In the previous sections, we learned to create one namespace in each document. You can create many namespaces in the same document, as long as the body of each namespace is appropriately delimited. Here is an example:

namespace RealEstate
{
    class House
    {
        public string propNumber;
        public double marketValue;
    }
}

namespace Dealership
{
    class Car
    {
    }
}

You can also create namespaces in various files. For example, you can create each namespace in its own file, or you can create a group of namespaces in one file and one or a group of namespaces in another file. After creating the files, to access the content of a namespace, you can qualify the name of the class.

Introduction to Nesting a Namespace

You can create one namespace inside another namespace. Creating a namespace inside another is referred to as nesting the namespace. The namespace inside another namespace is nested. To create a namespace inside another, simply type it as you would create another namespace. Here is an example:

namespace Business
{
    class House
    {
        public string propNumber;
        public double marketValue;
    }

    namespace Dealership
    {
    }
}

In the example above, the Dealership namespace is nested inside the Business namespace. After creating the desired namespaces, nested or not, you can create the desired class(es) inside the desired namespace.

To access anything that is included in a nested namespace, you use the period operator before calling a member of a namespace or before calling the next nested namespace. Here is an example:

@page
@model Valuable.Pages.FoundationsModel
@using Business;

@{
    Business.House property = new Business.House();

    property.propNumber = "D294FF";
    property.marketValue = 425880;

    Business.Dealership.Car vehicle = new Business.Dealership.Car();
    vehicle.marketValue = 38425.50;
}

<pre>=//= Altair Realtors =//=
    Properties Inventory
Property #: @prop.propNumber
Market Value:  @prop.marketValue
==============================
Car Leadership
Market Value: @vehicle.marketValue</pre>

This would produce:

=//= Altair Realtors =//=
    Properties Inventory
Property #: D294FF
Market Value:  425880
==============================
Car Leadership
Market Value: 38425.5

In the same way, you can nest as many namespaces inside other namespaces as you judge necessary.

Nesting a Namespace by Name

Another technique used to nest a namespace consists of starting to create one. Then, after its name, type a period followed by a name for the nested namespace. Here is an example:

namespace Geometry.Quadrilaterals
{
    
}

you can then add content to that namespace, including creating one or more classes in it. Here is an example that contains a class:

namespace Geometry.Quadrilaterals
{
    class Square
    {
        public double side;
    }
}

After creating the nested namespace and filling it with the desired content, you can access its member(s) by qualifying it(them). Here is an example:

@page
@model Valuable.Pages.FoundationsModel

@{
    Geometry.Quadrilaterals.Square sqr = new Geometry.Quadrilaterals.Square();
    
    sqr.side = 25.85;
}

<pre>=//= Geometry =//=
    Square
Side: @sqr.side</pre>

This would produce:

=//= Geometry =//=
    Square
Side: 25.85

In the same way, you can nest other namespaces inside one. Here are examples:

namespace Geometry.Quadrilaterals
{
    
}

namespace Geometry.Rounds
{
    
}

In the same way, you can create as many namespaces as necessary inside others. After nesting a namespace, You can add content to it. Here are examples:

namespace Geometry.Quadrilaterals
{
    class Square
    {
        public double side;
    }
}

namespace Geometry.Volumes.Elliptic
{
    class Cylinder
    {
        public double radius;
    }
}

As mentioned already, to access the content of a nested namespace, you can qualify the desired name. Here is an example:

@page
@model Valuable.Pages.FoundationsModel

@{
    Geometry.Quadrilaterals.Square sqr = new Geometry.Quadrilaterals.Square();
    Geometry.Volumes.Elliptic.Cylinder cyl = new Geometry.Volumes.Elliptic.Cylinder();
    sqr.side = 25.85;
    cyl.radius = 36.85;
}

<pre>=//= Geometry =//=
    Square
Side: @sqr.side
=======================
    Cylinder
Radius: @cyl.radius</pre>

This would produce:

=//= Geometry =//=
    Square
Side: 25.85
=======================
    Cylinder
Radius: 36.85

Class Overloading? No Way! Way...

Consider the following code that creates two classes in a single document:

class Number
{
    public int value;
}

class Number
{
    public int integral;
    public int precision;
}

This code will produce an error. This is because you cannot create two or more classes directly in a document if those classes use the same name. This means that you cannot overload the name of a class directly in a document. That is, you cannot have two classes with the same name in the same scope. One alternative is to put each class in its own namespace. Here is an example:

namespace Arithmetic
{
    class Numbers
    {
        public int value;
    }
}

namespace Algebra
{
    class Numbers
    {
        public int integral;
        public int precision;
    }
}

The Alias of a Namespace

If you have to access a namespace that is nested in another namespace, that too is nested, that is also nested, etc, the access can be long. As an alternative, you can create a shortcut that makes it possible to access a member of the nested namespace with a shorter label. That shortcut is called an alias. To create an alias for a namespace, in the top section where the inside member is needed, type using, followed by the desired name, followed by =, followed by the complete namespace. After doing this, you can then use the alias in place of the namespace.

Here is an example:

using Supplies;
using FunDepartmentStore.Personel;
using FunDepartmentStore.Inventory;
using Asian = Manufacturers.Foreign.Asia;

public class DepartmentStore
{
    Asian.Manufacturer dealer = new Asian.Manufacturer();
    dealer.CompanyName = "Peel Corp";
    dealer.ContactName = "Sylvain Yobo";
    dealer.ContactPhone = "(602) 791-8074";

    StoreItem si = new StoreItem();

    si.itemNumber = 613508;
    si.itemName = "Merino Crew Neck Cardigan";
    si.unitPrice = 80.00;
}

Public Classes and Namespaces

When you create a class in a namespace, you can mark that class with an access level, such as public. The rules are the same for a public class as we saw in the previous lesson. You just have to remember that the class is a member of the namespace. Here is an example:

namespace AltairRealtors
{
    public class House
    {
        public string PropertyType;
        public int    Bedrooms;
        public double marketValue;
    }
}

Partial Classes and Namespaces

When creating a class that is partial, you can make it a member of a namespace. There is no particular rule to follow, as long as you keep in mind that the class is a member of a namespace. Here is an example:

namespace NationalCensus
{
    partial class Person
    {
        public string FirstName;
        public string LastName ;
    }
}

Practical Learning: Ending the Lesson

Close your programming environment


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