Lesson 43 - Creating Constructor Methods

Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps

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In the previous lessons, we saw that fields – whether accessed directly or behind properties – are a collection of values that come to represent the current state description of the object they belong to. It’s generally a good idea to put a new object into a valid state as soon as possible before you start using it preferably at the time of instantiation. This would mean that you would want to construct the values for those fields – that represent that state – somewhere on the line of code where the new keyword is used. Luckily, there is a special type of method that allows you do to this called a “Constructor”.

Step 1: Create a New Project

For this lesson, create a new ASP.NET project called “CS-ASP_043” with a single resultLabel Server Control:


cs-asp-043---creating-constructor-methods.001


Without realizing it, you have been using Constructors all along. Whenever you create a new object, you are invoking a default, empty constructor by using the empty parentheses:


cs-asp-043---creating-constructor-methods.002


Step 2: Understanding the Default Empty Constructor

You may wonder how this is possible if you didn’t even write this method within the object’s class. The answer is that it is created in the background regardless. If you could see it, it would look like this:


cs-asp-043---creating-constructor-methods.003


Step 3: Understanding Constructor Requirements

The constructor is different from ordinary methods in three key ways. The constructor must:

  1. Have the same name as the class it belongs to.

  2. Be called at instantiation, after the new keyword.

  3. Not have a return type.

You can take control of exactly what the constructor does by explicitly writing its implementation details:


cs-asp-043---creating-constructor-methods.004


Step 4: Using Constructor Input Parameters for Initialization

Now, whenever a new Car object is created, it will take on these initialized values and retain them unless they are over-written. Better yet, you can let the values become initialized to whatever is supplied via the constructor’s input parameters:


cs-asp-043---creating-constructor-methods.005


Step 5: Using the ‘this’ Keyword

The “this” keyword simply refers to the class-level properties of the particular object’s instance and is necessary only when the constructor’s input parameters are named the exact same way. Now, you can initialize these values to whatever you want at the point of instantiation:


cs-asp-043---creating-constructor-methods.006


Add this public method to the Car class so that we can output the object’s values via the resultLabel:


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Then call the method in the Default class, which returns the formatted string. And then see the output when running the application:


cs-asp-043---creating-constructor-methods.008


cs-asp-043---creating-constructor-methods.009


Step 6: Overloading the Constructor

Since a constructor is just like any other kind of method, you can overload it with several definitions. Here, we can add to option for an initialized object – yet not specifically defined – in the case of no input parameters given at instantiation:

Tip:

To get the code-snippet shortcut for a constructor, type "ctor" and hit the tab key twice.


cs-asp-043---creating-constructor-methods.012


Step 7: Using Intellisense to Cycle Through Overloaded Constructors

Now, if we choose to instantiate a Car without any specific values given as input parameters, we still have a Car object that is in a valid, though not specifically defined, state:


cs-asp-043---creating-constructor-methods.013


And when you run the application you will, at least, have some kind of data shown:


cs-asp-043---creating-constructor-methods.014


Recall that many of the predefined objects we have been working with, such as DateTime(), have a variety of overloaded constructors that can put the object into a valid state. Go through the various constructors for DateTime() available to you, and try to imagine what the constructors look like behind these twelve overload options:


cs-asp-043---creating-constructor-methods.015


Related Articles in this Tutorial:

Lesson 1 - Series Introduction

Lesson 2 - Installing Visual Studio 2015

Lesson 3 - Building Your First Web App

Lesson 4 - Understanding What You Just Did

Lesson 5 - Working with Projects in Visual Studio

Lesson 6 - Simple Web Page Formatting in Visual Studio

Challenge 1

Solution 1

Lesson 7 - Variables and Data Types

Lesson 8 - Data Type Conversion

Lesson 9 - Arithmetic Operators

Lesson 10 - C# Syntax Basics

Challenge 2 - ChallengeSimpleCalculator

Solution - ChallengeSimpleCalculator

Lesson 11 - Conditional If Statements

Lesson 12 - The Conditional Ternary Operator

Challenge 3 - ChallengeConditionalRadioButton

Solution - Challenge Conditional RadioButton

Lesson 13 - Comparison and Logical Operators

Lesson 13 Challenge - First Papa Bob's Website

Solution - Challenge First Papa Bob's Website

Lesson 14 - Working with Dates and Times

Lesson 15 - Working With Spans of Time

Lesson 16 - Working with the Calendar Server Control

Challenge 4 - Challenge Days Between Dates

Solution - Challenge Days Between Dates

Lesson 17 - Page_Load and Page.IsPostBack

Lesson 18 - Setting a Break Point and Debugging

Lesson 19 - Formatting Strings

Challenge 5 - Challenge Epic Spies Assignment

Solution - Challenge Epic Spies Assignment

Lesson 20 - Maintaining State with ViewState

Lesson 21 - Storing Values in Arrays

Lesson 22 - Understanding Multidimensional Arrays

Lesson 23 - Changing the Length of an Array

Challenge 6 - Challenge Epic Spies Asset Tracker

Solution - Challenge Epic Spies Asset Tracker

Lesson 24 - Understanding Variable Scope

Lesson 25 - Code Blocks and Nested If Statements

Lesson 26 - Looping with the For Iteration Statement

Challenge 7 - Challenge For Xmen Battle Count

Solution - Challenge For Xmen Battle Count

Lesson 27 - Looping with the while() & do...while() Iteration Statements

Lesson 28 - Creating and Calling Simple Helper Methods

Lesson 29 - Creating Methods with Input Parameters

Lesson 30 - Returning Values from Methods

Lesson 31 - Creating Overloaded Methods

Lesson 32 - Creating Optional Parameters

Lesson 33 - Creating Names Parameters

Lesson 34 - Creating Methods with Output Parameters

Challenge 8 - Challenge Postal Calculator Helper Methods

Solution - Challenge Postal Calculator Helper Methods

Mega Challenge Casino

Solution - Mega Challenge Casino

Lesson 35 - Manipulating Strings

Challenge 9 - Phun With Strings

Solution - Challenge Phun With Strings

Lesson 36 - Introduction to Classes and Objects

Challenge - Hero Monster Classes Part 1

Solution - Hero Monster Classes Part 1

Challenge - Hero Monster Classes Part 2

Solution - Challenge Hero Monster Classes Part 2

Lesson 37 - Creating Class Files Creating Cohesive Classes and Code Navigation

Lesson 38 - Understanding Object References and Object Lifetime

Lesson 39 - Understanding the .NET Framework and Compilation

Lesson 40 - Namespaces and Using Directives

Lesson 41 - Creating Class Libraries and Adding References to Assemblies

Lesson 42 - Accessibility Modifiers, Fields and Properties

Lesson 43 - Creating Constructor Methods

Lesson 44 - Naming Conventions for Identifiers

Lesson 45 - Static vs Instance Members

Challenge 10 - Challenge Simple Darts

Solution - Challenge Simple Darts

Lesson 46 - Working with the List Collection

Lesson 47 - Object Initializers

Lesson 48 - Collection Initializers

Lesson 49 - Working with the Dictionary Collection

Lesson 50 - Looping with the foreach Iteration Statement

Lesson 51 - Implicitly-Typed Variables with the var Keyword

Challenge 11 - Challenge Student Courses

Solution - Challenge Student Courses

Mega Challenge War

Solution - Mega Challenge War

Lesson 52 - Creating GUIDs

Lesson 53 - Working with Enumerations

Lesson 54 - Understanding the switch() Statement

Lesson 55 - First Pass at the Separation of Concerns Principle

Lesson 56 - Understanding Exception Handling

Lesson 57 - Understanding Global Exception Handling

Lesson 58 - Understanding Custom Exceptions

Lesson 59 - Creating a Database in Visual Studio

Lesson 60 - Creating an Entity Data Model

Lesson 61 - Displaying the DbSet Result in an ASP.NET GridView

Lesson 62 - Implementing a Button Command in a GridView

Lesson 63 - Using a Tools-Centric Approach to Building a Database Application

Lesson 64 - Using a Maintenance-Driven Approach to Building a Database Application

Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database

Lesson 66 - Package Management with NuGet

Lesson 67 - NuGet No-Commit Workflow

Lesson 68 - Introduction the Twitter Bootstrap CSS Framework

Lesson 69 - Mapping Enum Types to Entity Properties in the Framework Designer

Lesson 70 - Deploying the App to Microsoft Azure Web Services Web Apps

Papa Bob's Mega Challenge

Papa Bob's Mega Solution Part 1 - Setting up the Solution

Papa Bob's Mega Solution Part 2 - Adding an Order to the Database

Papa Bob's Mega Solution Part 3 - Passing an Order from the Presentation Layer

Papa Bob's Mega Solution Part 4 - Creating the Order Form

Papa Bob's Mega Solution Part 5 - Adding Enums

Papa Bob's Mega Solution Part 6 - Creating an Order with Validation

Papa Bob's Mega Solution Part 7 - Calculating the Order Price

Papa Bob's Mega Solution Part 8 - Displaying the Price to the User

Papa Bob's Mega Solution Part 9 - Creating the Order Management Page


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