Lesson 49 - Working with the Dictionary Collection

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

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Dictionaries are Generic Collections that allow you to specify the type for not only the value stored as an item in the Collection, but also the type used for the key that refers to that item’s place within the Collection.

Step 1: Understanding the Dictionary Collection

Take, for instance, an ordinary List<string> which has an implied integer index that can be used to refer to each string item within the List. A Dictionary’s key is very similar to the index used in the List except that it doesn’t have to be an integer, but rather can be of any type (although, it is typically of type int or string).

This can make things easier when trying to find a particular item in a large set of items, and all you have to do is reference its key rather than iterate though the entire Collection looking for an index.

Step 2: Initializing a Dictionary Collection

For example, you might have a bunch of cars that you want to store in a Collection and be able to easily retrieve a car by its VIN number. Using a Dictionary, you can use the VIN number as the key and the object’s class type as the value, for example:


The format for a Dictionary collection is to declare a key that corresponds to a type (string, int, etc.) and give it a value type (of type Car, int, etc.) Here we’re using a string as the key to hold the VIN number which can be used to refer to a particular Car object (in other words, the key and the value are “paired” together). Here’s one way that we can add a Car, with a VIN as the key, into the Dictionary Collection:


Notice in the Add() method, you first pass in the key, then treat it in the same way you would a List collection. In addition to this, you can initialize the Dictionary just as you would a list, by doing the following:


Step 3: Retrieving Values from a Dictionary

Although you are now using a key instead of an array-like indexer, you can still iterate through the Dictionary by using the ElementAt() method and passing an argument that behaves like an ordinary indexer. The code below shows this in action, as well as printing out the key and value for each element:



Notice the different properties used, such as .Key and .Value. The .Key property holds the value of the Key that was determined for each index in the collection, whether a string, integer or anything else. The .Value Property, on the other hand, holds the value that the Key corresponds to. These properties exist to differentiate between the two parts of the Dictionary.

If you want to simply retrieve a single value out of the Collection you can use the TryGetValue() method which will return a value using the specified key and then output it to an existing variable:



What this code block does is create a local variable of type Car called v2, then in the if() statement, performs a check to ensure that a value exists for the key "V2". If it does not, it will exit out of the operation. However, if it does exist, the value will be stored in the v2 variable we created earlier. Then, the result is set to that, using the helper method we created.

Step 4: Removing an Item from the Dictionary

To remove an element in the Collection you can call the Remove() method and since it returns a bool -depending on if the element was successfully removed - you can wrap it in a conditional as follows:


This code checks to ensure that an entry exists in the Dictionary that corresponds to the Key "V1". If so, it uses the Remove() method to remove that value from the Dictionary. So that we can see that it successfully completed the operation, we print out a message in the resultLabel:


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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