Lesson 58 - Understanding Custom Exceptions

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

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This lesson will show you how to create custom Exceptions, which means creating your own class that can recognize, and allow you to handle a particular type of exception that you define within that class. This lesson, continues on from where we left off in Lesson 56, so begin by loading the CS-ASP_056 project.

Step 1: Add an Exceptions Folder

The first thing you will want to do is add a folder called “Exceptions” within the Domain layer, and store all of the custom Exception classes in this folder that relate to this layer:


cs-asp-058---understanding-custom-exceptions.001


This is a good rule to follow for code organization, as well as formatting an elegant namespace of ExceptionHandling.Domain.Exceptions. Now let’s add a class called “CharacterAlreadyDeadException” to the “Exceptions” folder by right-clicking it and selecting from the menu:

Add > Class


cs-asp-058---understanding-custom-exceptions.002


Step 2: Create a Custom Exception with Inheritance

To create a custom Exception, all we have to do is have the class inherit from the broader Exception class found in system.Exception. You achieve this inheritance by simply placing a colon after the class name, and then referencing the name of the class that you want to inherit from. This quietly imports all of the properties and methods you would find in the inherited class:


cs-asp-058---understanding-custom-exceptions.003


We can add additional methods and properties to this class, but it isn’t necessary. Now, in the GameActions class, let’s update the exceptions being thrown in the Battle() method to reflect our custom exception:


cs-asp-058---understanding-custom-exceptions.004


Step 3: Reference the Custom Namespace

This reference won’t be found by the compiler until you add the using statement for it at the top of this Class file:


cs-asp-058---understanding-custom-exceptions.005


Make sure to build this project, and then move on to the Default.aspx.cs file where we will want to catch this Exception where the call is made to the Battle() method in the existing Try code-block:


cs-asp-058---understanding-custom-exceptions.006


Now when you run the application you will see the thrown custom Exception that is caught here:


cs-asp-058---understanding-custom-exceptions.007


Step 4: Create a Custom Error Message

Now that we have our own custom Exception, we can make a much more specific error message. Go back to the custom class and add a property that stores the name of the character passed into the constructor wherever we end up throwing the Exception:


cs-asp-058---understanding-custom-exceptions.008


Now that the constructor takes an argument, let’s supply it where it’s called in the GameActions class:


cs-asp-058---understanding-custom-exceptions.009


Now when we reference this passed in CharacterName property value, we can output a more specific error message:


cs-asp-058---understanding-custom-exceptions.010


cs-asp-058---understanding-custom-exceptions.011


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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