Head First C#. 5th Edition

Spis treści książki

• Related books from OReilly
  • Other books in OReillys Head First series
• Table of Contents (the real thing)
•  
• How to use this Book Intro
  • Who is this book for?
    • Who should probably back away from this book?
  • We know what youre thinking
  • We know what your brain is thinking
  • Metacognition: thinking about thinking
  • Heres what WE did:
  • Heres what YOU can do to bend your brain into submission
  • README.md
  • The technical review team
  • Shoulders of giants
  • Acknowledgments
    • ...and a few more folks who have been so incredibly supportive over the years
• 1. Start Building Apps with C# Build something great...fast!
  • Learn C#...and learn to become a great developer
    • ...with a learning system thats effective and fun
  • Write code and explore C# with Visual Studio
    • Visual Studio is your free gateway to C#
  • Install Visual Studio Community Edition
  • Run Visual Studio
  • Create and run your first C# project in Visual Studio
  • You can use Visual Studio Code with Head First C#
  • Install the C# extensions
    • Change the C# debug console setting
  • Create and run your first project in Visual Studio Code
  • Set up Visual Studio Code for the next project
    • First open a folder, then add a project
    • The Command Palette
    • Install .NET MAUI before reading the rest of this chapter
    • If youre using Linux, youll need an Android device for the .NET MAUI projects
  • Lets build a game!
  • Break up large projects into smaller parts
  • Heres how youll build your game
  • Create a .NET MAUI project in Visual Studio
  • Create a .NET MAUI project in Visual Studio Code
  • Run your new .NET MAUI app
    • Stop your MAUI app
  • MAUI apps work on all of your devices
  • Heres the page that youll build
  • Start editing your XAML code
  • Add the XAML for a Button and a Label
  • Use a FlexLayout to make a grid of animal buttons
  • Write C# code to add the animals to the buttons
  • Start editing the PlayAgainButton event handler method
    • Add a C# statement to the event handler method
  • Add more statements to your event handler
  • Add animals to your buttons
  • Run your app!
    • Here are just a few things Git can do for you
  • Visual Studio makes it easy to use Git
  • Add C# code to handle mouse clicks
  • Enter the code for the event handler
  • Run your app and find all the pairs
    • Uh-ohtheres a bug in your code
    • When you find a bug, you need to sleuth it out
  • Finish the game by adding a timer
  • Add a timer to your games code
  • Finish the code for your game
    • Add a field to hold the time elapsed
    • Finish your TimerTick method
  • Even better ifs...
• 2. Variables, Statements, and Methods Dive into C# code
  • Take a closer look at the files in your console app
    • A statement performs one single action
  • Statements are the building blocks for your apps
  • Statements live inside methods
    • Methods do something
    • Methods help you organize your code
  • Your methods use variables to work with data
    • Declare your variables
    • Variables vary
    • You need to assign values to variables before you use them
    • A few useful types
  • Generate a new method to work with variables
  • Add code that uses operators to your method
  • Use the debugger to watch your variables change
  • Use code snippets to help write loops
  • Use operators to work with variables
  • if statements make decisions
    • if/else statements also do something if a condition isnt true
  • Loops perform an action over and over
    • while loops keep looping statements while a condition is true
    • do/while loops run the statements then check the condition
    • for loops run a statement after each loop
  • Some useful things to keep in mind about C# code
  • Controls drive the mechanics of your user interfaces
    • Meet some of the controls youll use in this book
  • Other controls youll use in this book
  • Build a .NET MAUI app to experiment with controls
  • Create a new app to experiment with controls
  • Explore your new MAUI app and figure out how it works
  • Add an Entry control to your app
  • Add properties to your Entry control
  • Make your Entry control update a Label control
  • Combine horizontal and vertical stack layouts
    • Youll nest one Layout inside another
  • Add a Picker control to display a list of choices
• Unity Lab #1 Explore C# with Unity
  • Unity is a powerful tool for game design
  • Download Unity Hub
  • Use Unity Hub to create a new project
    • Work with your project in the Unity editor
  • Take control of the Unity layout
    • Choose the Wide layout to match our screenshots
    • Set up Unity to work with Visual Studio
  • Your scene is a 3D environment
  • Unity games are made with GameObjects
  • Use the Move Gizmo to move your GameObjects
  • The Inspector shows your GameObjects components
  • Add a material to your Sphere GameObject
  • Rotate your sphere
    • Move the Scene view camera with the View Tool and Scene Gizmo
    • Get creative!
• 3. Namespaces and Classes Organizing your code
  • Classes help you organize your code
  • If code is useful, classes can help you reuse it
  • Some methods take parameters and return a value
  • Visual Studio helps you explore parameters and return values
  • Lets build an app that picks random cards
  • Youll use an array to store the cards
  • Create an app with a Main method
    • Create your PickRandomCards app without top-level statements
  • Add a class called CardPicker to your app
  • Use Quick Actions to remove unnecessary using lines
  • Convert between namespace styles
  • Use the new keyword to create an array of strings
    • Heres the code for your finished CardPicker class
  • Anas working on her next game
  • Anas game is evolving...
    • ...so how can Ana make things easier for herself?
  • Build a paper prototype for a classic game
  • Build a MAUI version of your random card app
    • Make your app accessible!
  • Make your MAUI app pick random cards
  • Reuse your CardPicker class
  • Add a using directive to use code in another namespace
  • Anas prototypes look great...
    • ...but what if she wants more than one enemy?
  • Ana can use objects to solve her problem
  • You use a class to build an object
    • An object gets its methods from its class
  • When you create a new object from a class, its called an instance of that class
  • A better solution for Ana...brought to you by objects
    • Theory and practice
  • An instance uses fields to keep track of things
    • Methods are what an object does. Fields are what an object knows.
  • Thanks for the memory
  • Whats on your apps mind
  • Sometimes code can be difficult to read
    • Extremely compact code can be especially problematic
  • Most code doesnt come with a manual
  • Use intuitive class and method names
  • Build a class to work with some guys
  • Theres an easier way to initialize objects with C#
  • Use the C# Interactive window or csi to run C# code
• 4. Data, Types, Objects, and References Managing your apps data
  • Owen could use our help!
    • Storytelling, fantasy, and mechanics
  • Character sheets store different types of data on paper
  • A variables type determines what kind of data it can store
  • C# has several types for storing integers
  • Types for storing really HUGE and really tiny numbers
  • Lets talk about strings
  • A literal is a value written directly into your code
    • Use suffixes to give your literals types
  • A variable is like a data to-go cup
    • Use the Convert class to explore bits and bytes
  • Other types come in different sizes too
  • 10 pounds of data in a 5-pound bag
  • Casting lets you copy values that C# cant automatically convert to another type
    • So what happened?
    • When you cast a value thats too big, C# adjusts it to fit its new container
  • C# does some conversions automatically
  • When you call a method, the arguments need to be compatible with the types of the parameters
  • Owen is constantly improving his game...
    • ...but the trial and error can be time-consuming
  • Lets help Owen experiment with ability scores
  • Fix the compiler error by adding a cast
    • Add a cast to get the AbilityScoreCalculator class to compile...
    • ...but theres still a bug!
    • Now we can finally fix Owens bugand get the REAL Sharpen answer
  • Use reference variables to access your objects
  • References are like sticky notes for your objects
  • If there arent any more references, your object gets garbage-collected
  • Multiple references and their side effects
  • Two references mean TWO variables that can change the same objects data
  • Objects use references to talk to each other
  • Arrays hold multiple values
    • Use each element in an array like its a normal variable
  • Arrays can contain reference variables
  • null means a reference points to nothing
    • Console.ReadLine returns a null when there are no lines available
  • Use the string? type when a string might be null
    • int.TryParse takes a string? parameter
  • Welcome to Sloppy Joes Budget House o Discount Sandwiches!
  • Sloppy Joes menu app uses a Grid layout
  • Grid controls
    • Use Grid properties to put a control in a cell
  • Define the rows and columns for a Grid
  • Create the Sloppy Joes menu app and set up the grid
    • Heres the XAML for the app
  • The C# code for the main page
  • Can we make the app more accessible?
    • Set the main header so the screen reader narrates it
    • Try setting the item1 labels SemanticProperties.Description instead
  • Use the SetValue method to change a controls semantic properties
• Unity Lab #2 Write C# Code for Unity
  • C# scripts add behavior to your GameObjects
  • Add a C# script to your GameObject
  • Write C# code to rotate your sphere
  • Add a breakpoint and debug your game
    • Use a hit count to skip frames
  • Use the debugger to understand Time.deltaTime
  • Add a cylinder to show where the Y axis is
  • Add fields to your class for the rotation angle and speed
  • Use Debug.DrawRay to explore how 3D vectors work
    • Use Unity to visualize vectors in 3D
  • Run the game to see the ray in the Scene view
    • Add a duration to the ray so it leaves a trail
  • Rotate your ball around a point in the scene
  • Use Unity to take a closer look at rotation and vectors
  • Get creative!
• 5. Encapsulation How objects keep their Secrets
  • Lets help Owen roll for damage
  • Create a console app to calculate damage
  • Design a MAUI version of the damage calculator app
    • How your damage calculator app will work
  • Tabletop talk (or maybe...dice discussion?)
  • Lets try to fix that bug
    • Oops! Its still not working
  • Use Debug.WriteLine to print diagnostic information
  • Its easy to accidentally misuse your objects
  • Encapsulation means keeping some data in a class private
    • When in doubt, make it private
  • Use encapsulation to control access to your classs methods and fields
  • But is the RealName field REALLY protected?
  • Private fields and methods can only be accessed from instances of the same class
  • Why encapsulation? Think of an object as an opaque box...
    • Encapsulation makes your classes...
  • Lets use encapsulation to improve the SwordDamage class
    • Is every member of the SwordDamage class public?
    • Are fields or methods being misused?
    • Is there calculation required after setting a field?
    • So what fields and methods really need to be public?
  • Encapsulation keeps your data safe
    • Lets use encapsulation in a class
  • Write a console app to test the PaintballGun class
    • Our class is well-encapsulated, but...
  • Properties make encapsulation easier
    • Replace the GetBalls and SetBalls methods with a property
  • Modify your top-level statements to use the Balls property
    • Debug your PaintballGun class to understand how the property works
  • Auto-implemented properties simplify your code
    • Use the prop snippet to create an auto-implemented property
  • Use a private setter to create a read-only property
    • Make the BallsLoaded setter private
  • What if we want to change the magazine size?
    • But theres a problem...how do we initialize MagazineSize?
  • Use a constructor with parameters to initialize properties
  • Specify arguments when you use the new keyword
  • Initialize fields and properties inline or in the constructor
  • Make the screen reader announce each roll
  • A few useful facts about methods and properties
• 6. Inheritance Your Objects Family Tree
  • Calculate damage for MORE weapons
  • Use a switch statement to match several candidates
  • One more thing...can we calculate damage for a dagger? And a mace? And a staff? and...
  • When your classes use inheritance, you only need to write your code once
  • Build up your class model by starting general and getting more specific
  • How would you design a zoo simulator?
  • Different animals have different behaviors
  • Every subclass extends its base class
    • C# always calls the most specific method
  • Any place where you can use a base class, you can use one of its subclasses instead
  • Use a colon to extend a base class
  • We know that inheritance adds the base class fields, properties, and methods to the subclass...
    • ...but some birds dont fly!
  • A subclass can override methods to change or replace members it inherited
  • Some members are only implemented in a subclass
  • Use the debugger to understand how overriding works
  • Build an app to explore virtual and override
  • A subclass can hide methods in the base class
    • Hiding methods vs. overriding methods
    • Use the new keyword when youre hiding methods
    • Use different references to call hidden methods
  • Use the override and virtual keywords to inherit behavior
  • A subclass can access its base class using the base keyword
  • When a base class has a constructor, your subclass needs to call it
  • A subclass and base class can have different constructors
  • Its time to finish the job for Owen
    • Use the debugger to really understand how these classes work
  • A class should do one thing
  • Build a beehive management system
  • How the Beehive Management System app works
  • The page uses a grid to lay out the controls for the UI
    • The Bee Jobs box uses a Border with a VerticalStackLayout
  • The Beehive Management System class model
  • All bees in the system extend the Bee class
  • All the constants are in their own static class
  • The worker bees extend the Bee class
  • The Queen class: how she manages the worker bees
  • Heres the code-behind for MainPage.xaml.cs
  • Feedback drives your beehive management game
    • Workers and honey are in a feedback loop
  • The Beehive Management System is turn-based... now lets convert it to real-time
  • Some classes should never be instantiated
  • An abstract class is an intentionally incomplete class
    • Lets plan a trip to another planet
  • Like we said, some classes should never be instantiated
    • Solution: use an abstract class
  • An abstract method doesnt have a body
  • Abstract properties work just like abstract methods
  • The Deadly Diamond of Death
• Unity Lab #3 GameObject Instances
  • Lets build a game in Unity!
  • Create a new material inside the Materials folder
  • Spawn a billiard ball at a random point in the scene
  • Use the debugger to understand Random.value
  • Turn your GameObject into a prefab
  • Create a script to control the game
  • Attach the GameController script to the Main Camera
  • Press Play to run your code
    • Watch the live instances in the Hierarchy window
  • Use the Inspector to work with GameObject instances
  • Use physics to keep balls from overlapping
  • Get creative!
• 7. Interfaces, Casting, and is Making classes keep their Promises
  • The beehive is under attack!
    • HiveDefender needs a DefendHive method because enemies can attack at any time
  • We could use casting to call the DefendHive method
    • but what if we add more Bee subclasses that can defend?
  • An interface defines methods and properties that a class must implement
    • but theres no limit to the number of interfaces a class can implement
  • Interfaces let unrelated classes do the same job
  • Get a little practice using interfaces
  • Fireside Chats
  • You cant instantiate an interface, but you can reference an interface
    • If you try to instantiate an interface, your code wont build
    • Use the interface to reference an object you already have
  • Pool Puzzle
  • Pool Puzzle Solution
  • Interface references are ordinary object references
  • The RoboBee 4000 can do a worker bees job without using valuable honey
  • The IWorkers Job property is a hack
  • Use is to check the type of an object
  • Use is to access methods in a subclass
  • What if we want different animals to swim or hunt in packs?
  • Use interfaces to work with classes that do the same job
    • Use the is keyword to check if the Animal is a swimmer or pack hunter
  • Safely navigate your class hierarchy with is
  • C# has another tool for safe type conversion: the as keyword
  • Use upcasting and downcasting to move up and down a class hierarchy
  • A quick example of upcasting
  • Upcasting turns your CoffeeMaker into an Appliance
  • Downcasting turns your Appliance back into a CoffeeMaker
  • Upcasting and downcasting work with interfaces too
  • Interfaces can inherit from other interfaces
  • Interfaces can have static members
  • Default implementations give bodies to interface methods
  • Add a ScareAdults method with a default implementation
  • Data binding updates MAUI controls automatically
  • Add data binding to the default MAUI app
  • Make Moods implement the INotifyPropertyChanged interface
  • Use the PropertyChanged event to make data binding work
  • Polymorphism means that one object can take many different forms
    • Keep your eyes open for polymorphism!
    • The four core principles of object-oriented programming
• 8. Enums and Collections Organizing your data
  • If a constructor just sets fields, use a primary constructor instead
  • A primary constructor can extend a base constructor
    • Overloaded constructors use this to call the primary constructor
  • Strings dont always work for storing categories of data
  • Enums let you work with a set of valid values
    • An enum defines a new type
  • Enums let you represent numbers with names
  • We could use an array to create a deck of cards
    • but what if you wanted to do more?
  • Arrays can be annoying to work with
  • Lists make it easy to store collections ofanything
  • Lists are more flexible than arrays
  • Lets build an app to store shoes
  • Generic collections can store any type
    • Generic lists are declared using <angle brackets>
  • You can use collection expressions to create Lists
  • Lets create a List of Ducks
    • Use a collection expression to create a List of Ducks
  • Sorting lists can be tricky
    • Lists know how to sort themselves
  • IComparable<Duck> helps your List sort its Ducks
    • An objects CompareTo method compares it to another object
  • Use IComparer to tell your List how to sort
    • Add an IComparer to your project
  • Create an instance of your comparer object
    • Multiple IComparer implementations, multiple ways to sort your objects
  • Comparers can do complex comparisons
  • Overriding a ToString method lets an object describe itself
    • Override the ToString method to see your Ducks in the IDE
  • Update your foreach loops to let your Ducks and Cards write themselves to the console
    • Add a ToString method to your Card object too
  • You can upcast an entire list using IEnumerable<T>
  • Use a Dictionary to store keys and values
    • How to use a Dictionary
  • The Dictionary functionality rundown
    • Your key and value can be different types
  • Write an app that uses a Dictionary
    • Use a collection initializer to create the Dictionary
  • And yet MORE collection types
    • Generic .NET collections implement IEnumerable
  • A queue is FIFOfirst in, first out
  • A stack is LIFOlast in, first out
  • CollectionView is a MAUI control built for displaying collections
  • ObservableCollection is a collection made for data binding
  • Add your Card class to the project
  • Use XAML to instantiate your objects for data binding
  • Modify your app to use a resource Dictionary
  • Modify the event handlers to use the resource Dictionary
  • Use what youve learned to build an app with two decks
• Unity Lab #4 User Interfaces
  • Add a score that goes up when the player clicks a ball
  • Add two different modes to your game
  • Add game mode to your game
  • Add a UI to your game
    • Use the 2D view to work with the Canvas
  • Set up the Text that will display the score in the UI
  • Add a Button that calls a method to start the game
  • Make the Play Again button and Score Text work
  • Finish the code for the game
  • Get creative!
• 9. LINQ and Lambdas Get Control of your data
  • Jimmys a Captain Amazing superfan...
  • ...but his collections all over the place
  • Use LINQ to query your collections
  • LINQ works with any sequence
    • LINQ methods enumerate your sequencesjust like foreach loops
  • LINQs query syntax
    • LINQ queries are built from clauses
  • LINQ works with objects
  • Use a LINQ query to finish the app for Jimmy
  • The var keyword lets C# figure out variable types for you
    • When you use var, C# figures out the variables type automatically
  • LINQ is versatile
  • LINQ queries arent run until you access their results
  • Use a group query to separate your sequence into groups
  • Use join queries to merge data from two sequences
  • Use the new keyword to create anonymous types
  • Unit tests help you make sure your code works
    • Add a second project to your solution for the unit tests
  • Start writing your first test method
    • Run the unit test
  • Give your unit tests access to the classes theyre testing
    • Add a project reference so the unit tests can access the classes they need to test
  • One project can only access public classes in another project
    • Make your JimmyLinq classes and enums public
  • Use the Arrange-Act-Assert pattern to write an effective test
    • Use Assert.AreEqual to check that a calculated value matches an expected value
  • Finish your first unit test
  • Write a unit test for the GetReviews method
  • Write unit tests to handle edge cases and weird data
  • Use the => operator to create lambda expressions
  • Refactor a clown with lambdas
  • Use the ?: operator to make your lambdas make choices
  • LINQ queries are made up of methods
    • You can use lambda expressions with methods that take a Func parameter
  • LINQ declarative syntax can be refactored into chained methods
  • Use the => operator to create switch expressions
  • Explore the Enumerable class
    • Enumerable.Empty creates an empty sequence of any type
    • Enumerable.Repeat repeats a value a specific number of times
    • So what exactly is an IEnumerable<T>?
  • Create an enumerable sequence by hand
  • Use yield return to create your own sequences
    • Use the debugger to explore yield return
  • Use yield return to refactor ManualSportSequence
    • Add an indexer to BetterSportSequence
  • Collectioncross
  • Collectioncross solution
• 10. Reading and Writing Files Save the last byte for me
  • .NET uses streams to read and write data
  • Different streams read and write different things
    • Things you can do with a stream:
  • A FileStream reads and writes bytes in a file
  • Write text to a file in three simple steps
  • The Swindler launches another diabolical plan
    • StreamWriter.WriteLine works just like Console.WriteLine
  • StreamWriter Magnets
  • StreamWriter Magnets Solution
  • Use a StreamReader to read a file
  • Data can go through more than one stream
  • Use the static File and Directory classes to work with files and directories
    • Things you can do with the static File class:
    • Things you can do with the static Directory class:
  • IDisposable makes sure objects are closed properly
    • Use the IDE to explore IDisposable
  • Avoid filesystem errors with using statements
    • Use multiple using statements for multiple objects
  • Use a MemoryStream to stream data to memory
    • Use Encoding.UTF8.GetString to convert byte arrays to strings
  • What happens to an object when its serialized?
  • But what exactly IS an objects state? What needs to be saved?
  • When an object is serialized, all of the objects it refers to get serialized too
  • Use JsonSerializer to serialize your objects
  • JSON only includes data, not specific C# types
  • Next up: well take a deep dive into our data
  • C# strings are encoded with Unicode
  • Visual Studio works really well with Unicode
  • .NET uses Unicode to store characters and text
  • C# can use byte arrays to move data around
  • Use a BinaryWriter to write binary data
  • Use BinaryReader to read the data back in
  • A hex dump lets you see the bytes in your files
    • How to make a hex dump of some plain text
  • Use StreamReader to build a hex dumper
  • Use Stream.Read to read bytes from a stream
  • Modify your hex dumper to read directly from the stream
  • Run your app from the command line
    • Use the args variable to access command-line arguments
  • Pass command-line arguments to an app run in the IDE
• Unity Lab #5 Raycasting
  • Create a new Unity project and start to set up the scene
  • Set up the camera
  • Create a GameObject for the player
  • Introducing Unitys navigation system
  • Install the AI Navigation package
  • Things youll do with navigation
  • Set up the NavMesh
    • Fix the carved-out hole in your NavMesh
  • Make your player automatically navigate the play area
• 11. Captain Amazing the Death of the Object
  • The life and death of an object
  • Use the GC class (with caution) to force garbage collection
  • Your last chance to DO something... your objects finalizer
  • When EXACTLY does a finalizer run?
    • You can SUGGEST to .NET that its time to collect the garbage
  • Finalizers cant depend on other objects
    • Dont use finalizers for serialization
  • A struct looks like an object...
    • ...but isnt an object
  • Values get copied; references get assigned
  • Structs are value types; objects are reference types
    • Heres what happened...
  • The stack vs. the heap: more on memory
  • Use out parameters to make a method return more than one value
  • Pass by reference using the ref modifier
  • Use optional parameters to set default values
  • A null reference doesnt refer to any object
  • Non-nullable reference types help you avoid NREs
    • Use encapsulation to prevent your property from ever being null
  • Nullable value types can be null...and handled safely
  • The null-coalescing operator ?? checks for nulls automatically
    • ?? checks for null and returns an alternative
    • ??= assigns a value to a variable only if its null
  • Captain Amazing...not so much
  • Records give your objects value equality automatically
  • Dont modify recordscopy them
    • Use the with keyword to create a modified copy of your Duck
  • Extension methods add new behavior to EXISTING classes
  • Extending a fundamental type: string
• 12. Exception Handling Putting out fires gets old
  • Your hex dumper reads a filename from the command line
    • But what happens if you give HexDump an invalid filename?
  • When your program throws an exception, the CLR generates an Exception object
  • All Exception objects inherit from System.Exception
  • There are some files you just cant dump
  • What happens when a method you want to call is risky?
  • Handle exceptions with try and catch
  • Use the debugger to follow the try/catch flow
  • If you have code that ALWAYS needs to run, use a finally block
  • Catch-all exceptions handle System.Exception
    • Avoid catch-all exception with multiple catch blocks
  • Pool Puzzle
  • Pool Puzzle Solution
  • Use the right exception for the situation
    • Catch custom exceptions that extend System.Exception
  • Exception Magnets
  • Exception Magnets Solution
  • Exception filters help you create precise handlers
  • The worst catch block EVER: catch-all plus comments
    • You should handle your exceptions, not bury them
  • Temporary solutions are OK (temporarily)
  • Use NuGet to add a logging library to your app
    • Packages add DLLs with classes
  • Add logging to your ExceptionExperiment app
• Unity Lab #6 Scene Navigation
  • Lets pick up where the last Unity Lab left off
  • Add a platform to your scene
  • Use bake options to make the platform walkable
  • Include the stairs and ramp in the NavMesh
  • Make the player navigate around the obstacles
    • Fix the moving obstacle
  • Get creative!
  • Thank you for reading our book!
    • But wait, theres more! Your journeys just begun...
    • Check out these essential (and amazing!) books written by our friends and colleagues, also published by
• Index

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