book

Head First C#, 3rd Edition

by Jennifer Greene, Andrew Stellman

September 2013

Beginner

1098 pages

31h 24m

English

O'Reilly Media, Inc.

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Dedication
A Note Regarding Supplemental Files
Advance Praise for Head First C#
Praise for other Head First books
How to Use this Book: Intro
Who is this book for?Who should probably back away from this book?We know what you’re thinking.And we know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE didHere’s what You can do to bend your brain into submissionRead meWhat version of Windows are you using?Using Windows 8 or later? Then you’ll start with Windows Store appsDon’t have Windows 8 or VS2013 yet? No problem—you’ll start with WPF appsYou’ll move on to create desktop applicationsThe technical review teamAcknowledgmentsSafari® Books Online
1. Start Building with C#: Build something cool, fast!
Why you should learn C#Here’s what the IDE automates for you...What you get with Visual Studio and C#...C# and the Visual Studio IDE make lots of things easyWhat you do in Visual Studio...What Visual Studio does for you...Aliens attack!Only you can help save the EarthHere’s what you’re going to buildStart with a blank applicationSet up the grid for your pageAdd controls to your gridUse properties to change how the controls lookControls make the game workYou’ve set the stage for the gameWhat you’ll do nextAdd a method that does somethingUse the IDE to create your own methodFill in the code for your methodFinish the method and run your programHere’s what you’ve done so farAdd timers to manage the gameplayMake the Start button workRun the program to see your progressAdd code to make your controls interact with the playerDragging humans onto enemies ends the gameYour game is now playableMake your enemies look like aliensAdd a splash screen and a tilePublish your appUse the Remote Debugger to sideload your appStart remote debugging
2. It’s all Just Code: Under the hood
When you’re doing this......the IDE does thisWhere programs come fromEvery program starts out as source code filesBuild the program to create an executableThe .NET Framework gives you the right tools for the jobYour program runs inside the Common Language RuntimeThe IDE helps you codeAnatomy of a programLet’s take a closer look at your codeTwo classes can be in the same namespaceYour programs use variables to work with dataDeclare your variablesVariables varyYou have to assign values to variables before you use themA few useful typesC# uses familiar math symbolsUse the debugger to see your variables changeLoops perform an action over and overUse a code snippet to write simple for loopsif/else statements make decisionsBuild an app from the ground upMake each button do somethingSet up conditions and see if they’re trueUse logical operators to check conditionsWindows Desktop apps are easy to buildRebuild your app for Windows DesktopYour desktop app knows where to startYou can change your program’s entry pointSo what happened?When you change things in the IDE, you’re also changing your codeWait, wait! What did that say?
3. Objects: Get Oriented!: Making code make sense
How Mike thinks about his problemsHow Mike’s car navigation system thinks about his problemsMike’s Navigator class has methods to set and modify routesSome methods have a return valueUse what you’ve learned to build a program that uses a classSo what did you just build?Mike gets an ideaHe could create three different Navigator classes...Mike can use objects to solve his problemYou use a class to build an objectAn object gets its methods from its classWhen you create a new object from a class, it’s called an instance of that classA better solution...brought to you by objects!Theory and practiceA little advice for the code exercisesAn instance uses fields to keep track of thingsMethods are what an object does. Fields are what the object knows.Let’s create some instances!Thanks for the memoryWhat’s on your program’s mindYou can use class and method names to make your code intuitiveGive your classes a natural structureLet’s build a class diagramClass diagrams help you organize your classes so they make senseBuild a class to work with some guysCreate a project for your guysBuild a form to interact with the guysThere’s an easier way to initialize objectsA few ideas for designing intuitive classes
4. Types and References: It’s 10:00. Do you know where your data is?
The variable’s type determines what kind of data it can storeA variable is like a data to-go cup10 pounds of data in a 5-pound bagEven when a number is the right size, you can’t just assign it to any variableSo what happened?When you cast a value that’s too big, C# will adjust it automaticallyC# does some casting automaticallyWhen you call a method, the arguments must be compatible with the types of the parametersDebug the mileage calculatorCombining = with an operatorObjects use variables, tooUsing an intUsing an objectRefer to your objects with reference variablesReferences are like labels for your objectIf there aren’t any more references, your object gets garbage-collectedMultiple references and their side effectsTwo references means TWO ways to change an object’s dataA special case: arraysUse each element in an array like it is a normal variableArrays can contain a bunch of reference variables, tooWelcome to Sloppy Joe’s Budget House o’ Discount Sandwiches!Objects use references to talk to each otherWhere no object has gone beforeBuild a typing gameControls are objects, just like any other object

I. C# Lab: A Day at the Races
5. Encapsulation: Keep your privates... Private
Kathleen is an event plannerWhat does the estimator do?You’re going to build a program for KathleenKathleen’s test driveEach option should be calculated individuallyIt’s easy to accidentally misuse your objectsEncapsulation means keeping some of the data in a class privateUse encapsulation to control access to your class’s methods and fieldsBut is the RealName field REALLY protected?Private fields and methods can only be accessed from inside the classEncapsulation makes your classes...Mike’s navigator program could use better encapsulationThink of an object as a black boxA few ideas for encapsulating classesEncapsulation keeps your data pristineA quick example of encapsulationProperties make encapsulation easierBuild an application to test the Farmer classUse automatic properties to finish the classFully encapsulate the Farmer classWhat if we want to change the feed multiplier?Use a constructor to initialize private fields
6. Inheritance: Your object’s family tree
Kathleen does birthday parties, tooWe need a BirthdayParty classHere’s what we’re going to do:Build the Part y Planner version 2.0One more thing...can you add a $100 fee for parties over 12?When your classes use inheritance, you only need to write your code onceDinner parties and birthday parties are both partiesBuild up your class model by starting general and getting more specificHow would you design a zoo simulator?Use inheritance to avoid duplicate code in subclassesDifferent animals make different noisesThink about what you need to overrideThink about how to group the animalsCreate the class hierarchyEvery subclass extends its base classC# always calls the most specific methodUse a colon to inherit from a base classWe know that inheritance adds the base class fields, properties, and methods to the subclass......but some birds don’t fly!A subclass can override methods to change or replace methods it inheritedAny place where you can use a base class, you can use one of its subclasses insteadA subclass can hide methods in the superclassHiding methods versus overriding methodsUse different references to call hidden methodsUse the new keyword when you’re hiding methodsUse the override and virtual keywords to inherit behaviorA subclass can access its base class using the base keywordWhen a base class has a constructor, your subclass needs one, tooThe base class constructor is executed before the subclass constructorNow you’re ready to finish the job for Kathleen!Build a beehive management systemHow you’ll build the beehive management systemUse inheritance to extend the bee management system
7. Interfaces and Abstract Classes: Making classes keep their promises
Let’s get back to bee-sicsLots of things are still the sameWe can use inheritance to create classes for different types of beesAn interface tells a class that it must implement certain methods and propertiesUse the interface keyword to define an interfaceNow you can create an instance of NectarStinger that does both jobsClasses that implement interfaces have to include ALL of the interface’s methodsGet a little practice using interfacesYou can’t instantiate an interface, but you can reference an interfaceInterface references work just like object referencesYou can find out if a class implements a certain interface with “is”Interfaces can inherit from other interfacesAny class that implements an interface that inherits from IWorker must implement its methods and propertiesThe RoboBee 4000 can do a worker bee’s job without using valuable honeyis tells you what an object implements; as tells the compiler how to treat your objectA CoffeeMaker is also an ApplianceUpcasting works with both objects and interfacesDowncasting lets you turn your appliance back into a coffee makerWhen downcasting fails, as returns nullUpcasting and downcasting work with interfaces, tooThere’s more than just public and privateAccess modifiers change visibilitySome classes should never be instantiatedAn abstract class is like a cross between a class and an interfaceLike we said, some classes should never be instantiatedSolution: use an abstract classAn abstract method doesn’t have a bodyThe four principles of object-oriented programmingPolymorphism means that one object can take many different formsKeep your eyes open for polymorphism in the next exercise!
8. Enums and Collections: Storing lots of data
Strings don’t always work for storing categories of dataEnums let you work with a set of valid valuesEnums let you represent numbers with namesWe could use an array to create a deck of cards......but what if you wanted to do more?Arrays are hard to work withLists make it easy to store collections of...anythingLists are more flexible than arraysLists shrink and grow dynamicallyGenerics can store any typeCollection initializers are similar to object initializersLet’s create a List of DucksHere’s the initializer for your List of DucksLists are easy, but SORTING can be trickyLists know how to sort themselvesIComparable<Duck> helps your list sort its ducksAn object’s CompareTo() method compares it to another objectUse IComparer to tell your List how to sortCreate an instance of your comparer objectMultiple IComparer implementations, multiple ways to sort your objectsIComparer can do complex comparisonsOverriding a ToString() method lets an object describe itselfUpdate your foreach loops to let your Ducks and Cards print themselvesAdd a ToString() method to your Card object, tooYou can upcast an entire list using IEnumerableCombine your birds into a single listYou can build your own overloaded methodsUse a dictionary to store keys and valuesThe dictionary functionality rundownYour key and value can be different typesBuild a program that uses a dictionaryAnd yet MORE collection types...Generic collections are an important part of the .NET FrameworkA queue is FIFO—First In, First OutA stack is LIFO—Last In, First Out
9. Reading and Writing Files: Save the last byte for me!
.NET uses streams to read and write dataDifferent streams read and write different thingsThings you can do with a stream:A FileStream reads and writes bytes to a fileWrite text to a file in three simple stepsThe Swindler launches another diabolical planReading and writing using two objectsData can go through more than one streamUse built-in objects to pop up standard dialog boxesShowDialog() pops up a dialog boxDialog boxes are just another WinForms controlDialog boxes are objects, tooUse the built-in File and Directory classes to work with files and directoriesThings you can do with File:Things you can do with Directory:Use file dialogs to open and save files (all with just a few lines of code)IDisposable makes sure your objects are disposed of properlyAvoid filesystem errors with using statementsUse multiple using statements for multiple objectsTrouble at workYou can help Brian out by building a program to manage his excusesWriting files usually involves making a lot of decisionsUse a switch statement to choose the right optionUse a switch statement to let your deck of cards read from a file or write itself out to oneAdd an overloaded Deck() constructor that reads a deck of cards in from a fileWhat happens to an object when it’s serialized?But what exactly IS an object’s state? What needs to be saved?When an object is serialized, all of the objects it refers to get serialized, too...Serialization lets you read or write a whole object graph all at onceYou’ll need a BinaryFormatter objectNow just create a stream and read or write your objectsIf you want your class to be serializable, mark it with the [Serializable] attributeLet’s serialize and deserialize a deck of cards.NET uses Unicode to store characters and textC# can use byte arrays to move data aroundUse a BinaryWriter to write binary dataUse BinaryReader to read the data back inYou can read and write serialized files manually, tooFind where the files differ, and use that information to alter themWorking with binary files can be trickyUse file streams to build a hex dumperHow to make a hex dumpWorking with hexStreamReader and StreamWriter will do just fine (for now)Use Stream.Read() to read bytes from a stream
II. C# Lab: The Quest
10. Designing Windows Store Apps with XAML: Taking your apps to the next level
Brian’s running Windows 8Windows Forms use an object graph set up by the IDEUse the IDE to explore the object graphWindows Store apps use XAML to create UI objectsRedesign the Go Fish! form as a Windows Store app pagePage layout starts with controlsRows and columns can resize to match the page sizeUse the grid system to lay out app pagesData binding connects your XAML pages to your classesContext, path, and bindingTwo-way binding can get or set the source propertyBind to collections with ObservableCollectionUse code for binding (without using any XAML at all!)XAML controls can contain text...and moreUse data binding to build Sloppy Joe a better menuUse static resources to declare your objects in XAMLUse a data template to display objectsINotifyPropertyChanged lets bound objects send updatesModify MenuMaker to notify you when the GeneratedDate property changes
11. Async, Await, and Data Contract Serialization: Pardon the interruption
Brian runs into file troubleWindows Store apps use await to be more responsiveUse the FileIO class to read and write filesUse the file pickers to locate file pathsBuild a slightly less simple text editorA data contract is an abstract definition of your object’s dataData contract serialization uses XML filesUse async methods to find and open filesKnownFolders helps you access high-profile foldersThe whole object graph is serialized to XMLStream some Guy objects to XML filesTake your Guy Serializer for a test driveUse a Task to call one async method from anotherBuild Brian a new Excuse Manager appSeparate the page, excuse, and Excuse ManagerCreate the main page for the Excuse ManagerAdd the app bar to the main pageBuild the ExcuseManager classAdd the code-behind for the page
12. Exception Handling: Putting out fires gets old
Brian needs his excuses to be mobileBut the program isn’t working!When your program throws an exception, .NET generates an Exception objectBrian’s code did something unexpectedAll exception objects inherit from ExceptionThe debugger helps you track down and prevent exceptions in your codeUse the IDE’s debugger to ferret out exactly what went wrong in the Excuse ManagerUh oh—the code’s still got problems...Handle exceptions with try and catchWhat happens when a method you want to call is risky?Use the debugger to follow the try/catch flowIf you have code that ALWAYS should run, use a finally blockUse the Exception object to get information about the problemUse more than one catch block to handle multiple types of exceptionsOne class throws an exception that a method in another class can catchBees need an OutOfHoney exceptionAn easy way to avoid a lot of problems: using gives you try and finally for freeException avoidance: implement IDisposable to do your own cleanupThe worst catch block EVER: catch-all plus commentsYou should handle your exceptions, not bury themTemporary solutions are OK (temporarily)A few simple ideas for exception handlingBrian finally gets his vacation......and things are looking up back home!
13. Captain Amazing: The Death of the Object
Your last chance to DO something... your object’s finalizerWhen EXACTLY does a finalizer run?You can SUGGEST to .NET that it’s time to collect the garbageDispose() works with using; finalizers work with garbage collectionFinalizers can’t depend on stabilityMake an object serialize itself in its Dispose()A struct looks like an object......but isn’t an objectValues get copied; references get assignedStructs are value types; objects are reference typesHere’s what happened...The stack vs. the heap: more on memoryUse out parameters to make a method return more than one valuePass by reference using the ref modifierUse optional parameters to set default valuesUse nullable types when you need nonexistent valuesNullable types help you make your programs more robust“Captain” Amazing...not so muchExtension methods add new behavior to EXISTING classesExtending a fundamental type: string
14. Querying Data and Building Apps With Linq: Get control of your data
Jimmy’s a Captain Amazing super-fan......but his collection’s all over the placeLINQ can pull data from multiple sources.NET collections are already set up for LINQLINQ makes queries easyLINQ is simple, but your queries don’t have to beJimmy could use some helpWindows Store apps use page-based navigationUse the IDE to explore app page navigationStart building Jimmy an appUse the new keyword to create anonymous typesLINQ is versatileAdd the new queries to Jimmy’s appLINQ can combine your results into groupsCombine Jimmy’s values into groupsUse join to combine two collections into one sequenceJimmy saved a bunch of doughUse semantic zoom to navigate your dataAdd semantic zoom to Jimmy’s appYou made Jimmy’s dayThe IDE’s Split App template helps you build apps for navigating data
15. Events and Delegates: What your code does when you’re not looking
Ever wish your objects could think for themselves?But how does an object KNOW to respond?When an EVENT occurs...objects listenWant to DO SOMETHING with an event? You need an event handlerOne object raises its event, others listen for it...Then, the other objects handle the eventConnecting the dotsUse a standard name when you add a method to raise an eventThe IDE generates event handlers for you automaticallyGeneric EventHandlers let you define your own event typesC# does implicit conversion when you leave out the new keyword and typeWindows Forms use many different eventsOne event, multiple handlersWindows Store apps use events for process lifetime managementUse the IDE to explore process lifetime management eventsAdd process lifetime management to Jimmy’s comicsXAML controls use routed eventsIsHitTestVisible determines if an element is “visible” to the pointer or mouseCreate an app to explore routed eventsConnecting event senders with event listeners“My people will get in touch with your people.”A delegate STANDS IN for an actual methodA delegate adds a new type to your projectDelegates in actionAn object can subscribe to an event......but that’s not always a good thing!Use a callback to control who’s listeningA callback is just a way to use delegatesMessageDialog uses the callback patternUse delegates to use the Windows settings charm
16. Architecting Apps with the mvvm Pattern: Great apps on the inside and outside
The Head First Basketball Conference needs an appBut can they agree on how to build it?Do you design for binding or for working with data?MVVM lets you design for binding and dataUse the MVVM pattern to start building the basketball roster appUser controls let you create your own controlsThe ref needs a stopwatchMVVM means thinking about the state of the appStart building the stopwatch app’s ModelEvents alert the rest of the app to state changesBuild the view for a simple stopwatchAdd the stopwatch ViewModelFinish the stopwatch appConverters automatically convert values for bindingConverters can work with many different typesStyles set properties on multiple controlsUse a resource dictionary to share resources between pagesVisual states make controls respond to changesUse DoubleAnimation to animate double valuesUse object animations to animate object valuesBuild an analog stopwatch using the same ViewModelUI controls can be instantiated with C# code, tooC# can build “real” animations, tooCreate a project and add the picturesCreate a user control to animate a pictureMake your bees fly around a pageUse ItemsPanelTemplate to bind controls to a CanvasCongratulations! (But you’re not done yet...)
III. C# Lab Invaders
A. Leftovers: The top 10 things we wanted to include in this book
#1. There’s so much more to Windows Store#2. The Basics...more basics...#3. Namespaces and assemblies...so what did I just do?Building a “Hello World” program from the command line#4. Use BackgroundWorker to make your WinForms responsive#5. The Type class and GetType()#6. Equality, IEquatable, and Equals()#7. Using yield return to create enumerable objects#8. RefactoringExtract a methodRename a variableConsolidate a conditional expression#9. Anonymous types, anonymous methods, and lambda expressions#10. LINQ to XMLSave and load XML filesQuery your dataRead data from an RSS feedDid you know that C# and the .NET Framework can...
B. Windows Presentation Foundation: WPF Learner’s Guide to Head First C#
Why you should learn WPFBuild WPF projects in Visual StudioHow to use this appendixChapter 1Start with a blank applicationSet up the grid for your windowAdd controls to your gridUse properties to change how the controls lookControls make the game workYou’ve set the stage for the gameWhat you’ll do nextAdd a method that does somethingUse the IDE to create your own methodFill in the code for your methodFinish the method and run your programHere’s what you’ve done so farAdd timers to manage the gameplayMake the Start button workRun the program to see your progressAdd code to make your controls interact with the playerDragging humans onto enemies ends the gameYour game is now playableMake your enemies look like aliensChapter 2Use the debugger to see your variables changeBuild an app from the ground upChapter 10WPF applications use XAML to create UI objectsRedesign the Go Fish! form as a WPF applicationPage layout starts with controlsRows and columns can resize to match the page sizeUse data binding to build Sloppy Joe a better menuUse static resources to declare your objects in XAMLUse a data template to display objectsINotifyPropertyChanged lets bound objects send updatesModify MenuMaker to notify you when the GeneratedDate property changesChapter 11C# programs can use await to be more responsiveStream some Guy objects to a fileTake your Guy Serializer for a test driveChapter 12Brian’s code did something unexpectedUse the IDE’s debugger to ferret out exactly what went wrong in the Excuse ManagerUh-oh—the code’s still got problems...Handle exceptions with try and catchWhat happens when a method you want to call is risky?Use the debugger to follow the try/catch flowIf you have code that should ALWAYS run, use a finally blockChapter 14Build a WPF comic query applicationChapter 15XAML controls use routed eventsIsHitTestVisible determines if an element is “visible” to the pointer or mouseCreate an app to explore routed eventsChapter 16Use the MVVM pattern to start building the basketball roster appUser controls let you create your own controlsBuild the view for a simple stopwatchFinish the stopwatch appConverters automatically convert values for bindingConverters can work with many different typesBuild an analog stopwatch using the same ViewModelUI controls can be instantiated with C# code, tooCreate a user control to animate a pictureMake your bees fly around a pageUse ItemsPanelTemplate to bind controls to a CanvasCongratulations! (But you’re not done yet...)
Index
About the Authors
Copyright

Content preview from Head First C#, 3rd Edition

Chapter 15. Events and Delegates: What your code does when you’re not looking

Your objects are starting to think for themselves.

You can’t always control what your objects are doing. Sometimes things...happen. And when they do, you want your objects to be smart enough to respond to anything that pops up. And that’s what events are all about. One object publishes an event, other objects subscribe, and everyone works together to keep things moving. Which is great, until you want your object to take control over who can listen. That’s when callbacks will come in handy.

Ever wish your objects could think for themselves?

Suppose you’re writing a baseball simulator. You’re going to model a game, sell the software to the Yankees (they’ve got deep pockets, right?), and make a million bucks. You create your Ball, Pitcher, Umpire, and Fan objects, and a whole lot more. You even write code so that the Pitcher object can catch a ball.

Now you just need to connect everything together. You add an OnBallInPlay() method to Ball, and now you want your Pitcher object to respond with its event handler method. Once the methods are written, you just need to tie the separate methods together:

Note

That’s a commonly used way of naming methods—we’ll talk more about it later.

But how does an object KNOW to respond? ...

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