Lesson 53 - Working with Enumerations

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

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In this lesson, we're going to talk about enumerations – or rather “enums” as their known in C#. An enum is a special data type that can hold , at any moment, one of a limited set of possible values that you determine. To demonstrate this, imagine that we're creating an application that collects information about pet ownership. You will want to create a pet class, and capture the name of the pet, the age of the pet, and the type of pet.


Step 1: Why Use an Enum?

Now, the pet type might be one of several different available options: a dog, a cat, a fish, an elephant, and so on. However we should know ahead of time that it is a limited set, and that we can’t declare just anything as a valid pet type:


It would be difficult to account for these various possibilities using a string data type for holding the PetType (in this case, you would probably create a property that checks for valid entries via a conditional statement in the “setter”). However, an enum – by definition – allows you to restrict your set of options only to values that are relevant. Here is how you create an enum:


And now you can change the data type, in the Pet class, from string to PetType:


And now, when you reference the Type property, you can only set it to one of the available options:


Step 2: Using Intellisense to See Enum Options

Perhaps more importantly, Intellisense recognizes that we have a limited set of options and stops us from using an invalid value at compile time:


You may be wondering what the real value is in limiting possibilities in your code. After all, somebody might have an uncommon pet such as a Zebra, or an Eel. By using an enum, you would just modify your code to accept those types of pets while retaining the added benefit of not allowing something seemingly innocuous – such as wanting a Velociraptor as a pet – to end up breaking your code.

Enumerations are used all over the place in the .NET Framework Class Library, primarily because they limit the possible values that you can pass into methods or set into properties. If the creators of the .NET Framework Class Library allowed you to pass any value you wanted to into a given method/property, there is a higher chance that an incorrect value will be provided and make for more debugging problems in your code.


Don't think of creating constraints inside of software development as necessarily a bad thing. In fact, it's often a great thing, in that it helps you to write more robust and error-free code than would otherwise be possible. The greatest challenge with writing code is simplifying everything, and enums can be an important part of that simplification process.

Step 3: Create a New Project

Create a new ASP.NET project for this lesson and call it “CS-ASP_053.” Add the following Server Controls and programmatic IDs to the Default.aspx file:

  1. heroNameTextBox

  2. heroTypeDropDown

  3. Button1

  4. resultLabel



The second Server Control is a DropDownList. That can be accessed via the ToolBox:


Next, in Default.aspx.cs create a public enum that is incorporated via a property in a public Character class:


Step 4: Demonstrating Error-Prevention via Enums

Now, in the Page_Load() method you can create a new Character and select its enum value:



This is a good place to give an example of why limiting user input is valuable. In software development, you want to do all you can to limit or eliminate dependency on open-ended data types like "magic strings", which are simply string input from users that could be any value. If we accepted a "magic string" instead of an enum for this type, it would be subject to all sorts of errors that won’t even be caught by the compiler and would require complete consistency on our part:


Another thing worth mentioning with the enum definition is that it can be nested within another class. In this case, it may actually make sense to considering that the class and enum seem to conceptually belong together:


Now, we need to modify our references because the CharacterType enum is accessed through the Character class first.


Step 6: Populate the DropDownList in the Designer

Let’s now demonstrate how we can use the DropDownList to select amongst the available values for the Character.CharacterType enum. We first have to populate the DropDownList with a set of default options. Click on the arrow beside the Server Control in the Design View, and select “Edit Items…”:


Then simply click the “Add” button and modify the displayed text and stored value for each item:


Back in the Button1_Click() method we (1) created a local variable to store the enum and then (2) returned to it a value chosen from the DropDownList Control. This value then (3) gets input through the static Enum.TryParse() method and, if it successfully parsed the string to an enum, it (4) gets stored into the hero.Type enum property:


You can also add a special message, to the bottom of the Button1_Click() method, depending on the enum value that is currently selected once the button is pressed:


Step 7: Comment Out Page_Load() and Run the Application

Now the run the application, but first be sure to comment out the Page_Load() method as it will just interfere with the results:



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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