Head First C#, 5th Edition

Table of contents

1. 1. Start Building apps with C#: Build Something Great…Fast!
   1. Why you should learn C#
   2. Write code and explore C# with Visual Studio
      1. Visual Studio is your gateway to C#
   3. Install Visual Studio Community Edition
   4. Run Visual Studio
   5. Create your first project in Visual Studio – Windows edition
   6. Create your first project in Visual Studio – Mac edition
   7. Let’s build a game!
   8. Break up large projects into smaller parts
   9. Here’s how you’ll build your game
   10. Create a .NET MAUI project in Visual Studio – Windows edition
   11. Create a .NET MAUI project in Visual Studio – Mac edition
   12. Run your new .NET MAUI app
       1. Stop your MAUI app
   13. MAUI apps work on all of your devices
   14. Here’s the page that you’ll build
   15. Start editing your XAML code
   16. Add the XAML for a Button and a Label
   17. Use a FlexLayout to make a grid of animal buttons
   18. Write C# code to add the animals to the buttons
   19. Start editing the PlayAgainButton event handler method
       1. Add a C# statement to the event handler method
   20. Add more statements to your event handler
   21. Add animals to your buttons
   22. Run your app!
       1. Here are just a few things Git can do for you
   23. Visual Studio makes it easy to use Git
   24. Add C# code to handle mouse clicks
   25. Enter the code for the event handler
   26. Run your app and find all the pairs
       1. Uh-oh – there’s a bug in your code
       2. When you find a bug, you need to sleuth it out
   27. Finish the game by adding a timer
   28. Add a timer to your game’s code
   29. Finish the code for your game
       1. Add a field to hold the time elapsed
       2. Finish your TimerTick method
   30. Even better ifs…
2. 2. Variables, Statements, and Methods: Dive into C# code
   1. Take a closer look at the files in your console app
      1. A statement performs one single action
   2. Statements are the building blocks for your apps
   3. Statements live inside of methods
      1. Methods do something
      2. Methods help you organize your code
   4. Your methods use variables to work with data
      1. Declare your variables
      2. Variables vary
      3. You need to assign values to variables before you use them
      4. A few useful types
   5. Generate a new method to work with variables
   6. Add code that uses operators to your method
   7. Use the debugger to watch your variables change
   8. Use operators to work with variables
   9. “if” statements make decisions
      1. if/else statements also do something if a condition isn’t true
   10. Loops perform an action over and over
       1. while loops keep looping statements while a condition is true
       2. do/while loops run the statements then check the condition
       3. for loops run a statement after each loop
   11. Use code snippets to help write loops
   12. Some useful things to keep in mind about C# code
   13. Controls drive the mechanics of your user interfaces
       1. Meet some of the controls you’ll use in this book
   14. Other controls you’ll use in this book
   15. Build a .NET MAUI app to experiment with controls
   16. Create a new app to experiment with controls
   17. Explore your new MAUI app and figure out how it works
   18. Add an Entry control to your app
   19. Add properties to your Entry control
   20. Make your Entry control update a Label
   21. Combine horizontal and vertical stack layouts
       1. You’ll nest one Layout inside another
   22. Add a Picker control to display a list of choices
3. 3. Namespaces and Classes: Organizing your code
   1. Classes help you organize your code
   2. If code is useful, classes can help you reuse it
   3. Some methods take parameters and return a value
   4. Visual Studio helps you explore parameters and return values
   5. Let’s build an app that picks random cards
   6. You’ll use an array to store the cards
   7. Create an app with a Main method
   8. Create your PickRandomCards app without top-level statements
   9. Add a class called CardPicker to your app
   10. Use Quick Actions to remove unnecessary ‘using’ lines
   11. Convert between namespace styles
   12. Use the new keyword to create an array of strings
   13. Here’s the code for your finished CardPicker class
   14. Ana’s working on her next game
   15. Ana’s game is evolving…
   16. …so how can Ana make things easier for herself?
   17. Build a paper prototype for a classic game
   18. Build a MAUI version of your random card app
   19. Make your app accessible!
   20. Make your MAUI app pick random cards
   21. Reuse your the CardPicker class
   22. Add a using directive to use code in another namespace
   23. Ana’s prototypes look great…
       1. …but what if she wants more than one enemy?
   24. Ana can use objects to solve her problem
   25. You use a class to build an object
       1. An object gets its methods from its class
   26. When you create a new object from a class, it’s called an instance of that class
   27. A better solution for Ana…brought to you by objects
       1. Theory and practice
   28. An instance uses fields to keep track of things
       1. Methods are what an object does. Fields are what the object knows.
   29. Thanks for the memory
   30. What’s on your app’s mind
   31. Sometimes code can be difficult to read
       1. Extremely compact code can be especially problematic
   32. Most code doesn’t come with a manual
   33. Use intuitive class and method names
   34. Build a class to work with some guys
   35. There’s an easier way to initialize objects with C#
   36. Use the C# Interactive window or csi to run C# code
4. 4. Data, Types, Objects, and References: Managing your App’s Data
   1. Owen could use our help!
      1. Storytelling, fantasy, and mechanics
   2. Character sheets store different types of data on paper
   3. A variable’s type determines what kind of data it can store
   4. C# has several types for storing integers
   5. Types for storing really HUGE and really tiny numbers
   6. Let’s talk about strings
   7. A literal is a value written directly into your code
      1. Use suffixes to give your literals types
   8. A variable is like a data to-go cup
      1. Use the Convert class to explore bits and bytes
   9. Other types come in different sizes, too
   10. 10 pounds of data in a 5-pound bag
   11. Casting lets you copy values that C# can’t automatically convert to another type
       1. So what happened?
       2. When you cast a value that’s too big, C# adjusts it to fit its new container
   12. C# does some conversions automatically
   13. When you call a method, the arguments need to be compatible with the types of the parameters
   14. Owen is constantly improving his game...
   15. ...but the trial and error can be time-consuming
   16. Let’s help Owen experiment with ability scores
   17. Fix the compiler error by adding a cast
       1. Add a cast to get the AbilityScoreCalculator class to compile...
       2. ...but there’s still a bug!
       3. Now we can finally fix Owen’s bug—and get the REAL “Sharpen” answer
   18. Use reference variables to access your objects
   19. References are like sticky notes for your objects
   20. If there aren’t any more references, your object gets garbage-collected
   21. Multiple references and their side effects
   22. Two references mean TWO variables that can change the same object’s data
   23. Objects use references to talk to each other
   24. Arrays hold multiple values
       1. Use each element in an array like it’s a normal variable
   25. Arrays can contain reference variables
   26. null means a reference points to nothing
       1. Console.ReadLine returns a null when there are no lines available
   27. Use the string? type when a string might be null
       1. int.TryParse takes a string? parameter
   28. Welcome to Sloppy Joe’s Budget House o’ Discount Sandwiches!
   29. Sloppy Joe’s menu app uses a Grid layout
   30. Grid controls
       1. Use Grid properties to put a control in a cell
   31. Define the rows and columns for a Grid
   32. Create the Sloppy Joe’s menu app and set up the grid
       1. Here’s the XAML for the app.
   33. The C# code for the main page
   34. Can we make the app more accessible?
       1. Set the main header so the screen reader narrates it
       2. Try setting the item1 label’s SemanticProperties.Description instead
   35. Use the SetValue method to change a control’s semantic properties
5. 5. Encapsulation: How Objects Keep their Secrets
   1. Let’s help Owen roll for damage
   2. Create a console app to calculate damage
   3. Design a MAUI version of the damage calculator app
      1. How your damage calculator app will work
   4. Tabletop talk (or maybe... dice discussion?)
   5. Let’s try to fix that bug
      1. Oops! It’s still not working
   6. Use Debug.WriteLine to print diagnostic information
   7. It’s easy to accidentally misuse your objects
   8. Encapsulation means keeping some data in a class private
      1. When in doubt, make it private
   9. Use encapsulation to control access to your class’s methods and fields
   10. But is the RealName field REALLY protected?
   11. Private fields and methods can only be accessed from instances of the same class
   12. Why encapsulation? Think of an object as an opaque box...
       1. Encapsulation makes your classes...
   13. A few ideas for encapsulating classes
   14. Let’s use encapsulation to improve the SwordDamage class
       1. Is every member of the SwordDamage class public?
       2. Are fields or methods being misused?
       3. Is there calculation required after setting a field?
       4. So what fields and methods really need to be public?
   15. Encapsulation keeps your data safe
       1. Let’s use encapsulation in a class
   16. Write a console app to test the PaintballGun class
       1. Our class is well-encapsulated, but...
   17. Properties make encapsulation easier
       1. Replace the GetBalls and SetBalls methods with a property
   18. Modify your top-level statements to use the Balls property
       1. Debug your PaintballGun class to understand how the property works
   19. Auto-implemented properties simplify your code
       1. Use the prop snippet to create an auto-implemented property
   20. Use a private setter to create a read-only property
       1. Make the BallsLoaded setter private
   21. What if we want to change the magazine size?
       1. But there’s a problem...how do we initialize MagazineSize?
   22. Use a constructor with parameters to initialize properties
   23. Specify arguments when you use the “new” keyword
   24. Pool Puzzle
   25. Pool Puzzle Solution
   26. Initialize fields and properties inline or in the constructor
   27. Make the screen reader announce each roll
   28. A few useful facts about methods and properties
   29. Objectcross
6. 6. Inheritance: Your Object’s Family Tree
   1. Calculate damage for MORE weapons
   2. Use a switch statement to match several candidates
   3. One more thing...can we calculate damage for a dagger? and a mace? and a staff? and...
   4. When your classes use inheritance, you only need to write your code once
   5. Build up your class model by starting general and getting more specific
   6. How would you design a zoo simulator?
   7. Different animals have different behaviors
   8. Every subclass extends its base class
      1. C# always calls the most specific method
   9. Any place where you can use a base class, you can use one of its subclasses instead
   10. Use a colon to extend a base class
   11. We know that inheritance adds the base class fields, properties, and methods to the subclass...
       1. ...but some birds don’t fly!
   12. A subclass can override methods to change or replace members it inherited
   13. Some members are only implemented in a subclass
   14. Use the debugger to understand how overriding works
   15. Build an app to explore virtual and override
   16. A subclass can hide methods in the base class
       1. Thank you for returning my precious jewels!
       2. Hiding methods versus overriding methods
       3. Use the new keyword when you’re hiding methods
       4. Use different references to call hidden methods
   17. Use the override and virtual keywords to inherit behavior
   18. A subclass can access its base class using the base keyword
   19. When a base class has a constructor, your subclass needs to call it
   20. A subclass and base class can have different constructors
   21. It’s time to finish the job for Owen
       1. Use the debugger to really understand how these classes work
   22. A class do should just one thing
   23. Build a beehive management system
   24. How the Beehive Management System app works
   25. The page uses a grid to lay out the controls for the UI
       1. The Bee Jobs box uses a Border with a VerticalStackLayout
   26. The beehive management system class model
   27. All bees in the system extend the Bee class
   28. All the constants are in their own static class
   29. The worker bees extend the Bee class
   30. The Queen class: how she manages the worker bees
   31. Here’s the code-behind for MainPage.xaml.cs
   32. Feedback drives your Beehive Management game
       1. Workers and honey are in a feedback loop
   33. The Beehive Management System is turn-based... now let’s convert it to real-time
   34. Some classes should never be instantiated
   35. An abstract class is an intentionally incomplete class
       1. Let’s plan a trip to another planet
   36. Like we said, some classes should never be instantiated
       1. Solution: use an abstract class
   37. An abstract method doesn’t have a body
   38. Abstract properties work just like abstract methods
   39. The Deadly Diamond of Death
7. 7. Interfaces, Casting, and “is”: Making Classes keep their Promises
   1. The beehive is under attack!
   2. HiveDefender needs a DefendHive method because enemies can attack at any time
   3. We could use casting to call the DefendHive method…
      1. …but what if we add more Bee subclasses that can defend?
   4. An interface defines methods and properties that a class must implement…
      1. …but there’s no limit to the number of interfaces a class can implement
   5. Interfaces let unrelated classes do the same job
   6. Get a little practice using interfaces
      1. What’s the picture ?
   7. What’s the declaration ?
   8. You can’t instantiate an interface, but you can reference an interface
      1. If you try to instantiate an interface, your code won’t build
      2. Use the interface to reference an object you already have
   9. Interface references are ordinary object references
   10. The RoboBee 4000 can do a worker bee’s job without using valuable honey
   11. The IWorker’s Job property is a hack
   12. Use “is” to check the type of an object
   13. Use “is” to access methods in a subclass
   14. What if we want different animals to swim or hunt in packs?
   15. Use interfaces to work with classes that do the same job
       1. Use the “is” keyword to check if the Animal is a swimmer or pack hunter
   16. Safely navigate your class hierarchy with “is”
   17. C# has another tool for safe type conversion: the “as” keyword
   18. Use upcasting and downcasting to move up and down a class hierarchy
   19. A quick example of upcasting
   20. Upcasting turns your CoffeeMaker into an Appliance
   21. Downcasting turns your Appliance back into a CoffeeMaker
   22. Upcasting and downcasting work with interfaces, too
   23. Interfaces can inherit from other interfaces
   24. Interfaces can have static members
   25. Default implementations give bodies to interface methods
   26. Add a ScareAdults method with a default implementation
   27. Data binding updates MAUI controls automatically
   28. Add data binding to the default MAUI app
   29. Make Moods implement the INotifyPropertyChanged interface
   30. Use the PropertyChanged event to make data binding work
   31. Polymorphism means that one object can take many different forms
       1. Keep your eyes open for polymorphism!
       2. The four core principles of object-oriented programming
8. About the Authors