60分钟学会C#

// Single-line comments start with // /* Multi-line comments look like this */ /// <summary> /// This is an XML documentation comment which can be used to generate external /// documentation or provide context help within an IDE /// </summary> //public void MethodOrClassOrOtherWithParsableHelp() {} // Specify the namespaces this source code will be using // The namespaces below are all part of the standard .NET Framework Class Libary using System; using System.Collections.Generic; using System.Dynamic; using System.Linq; using System.Net; using System.Threading.Tasks; using System.IO; // But this one is not: using System.Data.Entity; // In order to be able to use it, you need to add a dll reference // This can be done with the NuGet package manager: `Install-Package EntityFramework` // Namespaces define scope to organize code into "packages" or "modules" // Using this code from another source file: using Learning.CSharp; namespace Learning.CSharp { // Each .cs file should at least contain a class with the same name as the file // you're allowed to do otherwise, but shouldn't for sanity. public class LearnCSharp { // BASIC SYNTAX - skip to INTERESTING FEATURES if you have used Java or C++ before public static void Syntax() { // Use Console.WriteLine to print lines Console.WriteLine("Hello World"); Console.WriteLine( "Integer: " + 10 + " Double: " + 3.14 + " Boolean: " + true); // To print without a new line, use Console.Write Console.Write("Hello "); Console.Write("World"); /////////////////////////////////////////////////// // Types & Variables // // Declare a variable using <type> <name> /////////////////////////////////////////////////// // Sbyte - Signed 8-bit integer // (-128 <= sbyte <= 127) sbyte fooSbyte = 100; // Byte - Unsigned 8-bit integer // (0 <= byte <= 255) byte fooByte = 100; // Short - 16-bit integer // Signed - (-32,768 <= short <= 32,767) // Unsigned - (0 <= ushort <= 65,535) short fooShort = 10000; ushort fooUshort = 10000; // Integer - 32-bit integer int fooInt = 1; // (-2,147,483,648 <= int <= 2,147,483,647) uint fooUint = 1; // (0 <= uint <= 4,294,967,295) // Long - 64-bit integer long fooLong = 100000L; // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807) ulong fooUlong = 100000L; // (0 <= ulong <= 18,446,744,073,709,551,615) // Numbers default to being int or uint depending on size. // L is used to denote that this variable value is of type long or ulong // Double - Double-precision 64-bit IEEE 754 Floating Point double fooDouble = 123.4; // Precision: 15-16 digits // Float - Single-precision 32-bit IEEE 754 Floating Point float fooFloat = 234.5f; // Precision: 7 digits // f is used to denote that this variable value is of type float // Decimal - a 128-bits data type, with more precision than other floating-point types, // suited for financial and monetary calculations decimal fooDecimal = 150.3m; // Boolean - true & false bool fooBoolean = true; // or false // Char - A single 16-bit Unicode character char fooChar = 'A'; // Strings -- unlike the previous base types which are all value types, // a string is a reference type. That is, you can set it to null string fooString = ""escape" quotes and add (new lines) and (tabs)"; Console.WriteLine(fooString); // You can access each character of the string with an indexer: char charFromString = fooString[1]; // => 'e' // Strings are immutable: you can't do fooString[1] = 'X'; // Compare strings with current culture, ignoring case string.Compare(fooString, "x", StringComparison.CurrentCultureIgnoreCase); // Formatting, based on sprintf string fooFs = string.Format("Check Check, {0} {1}, {0} {1:0.0}", 1, 2); // Dates & Formatting DateTime fooDate = DateTime.Now; Console.WriteLine(fooDate.ToString("hh:mm, dd MMM yyyy")); // You can split a string over two lines with the @ symbol. To escape " use "" string bazString = @"Here's some stuff on a new line! ""Wow!"", the masses cried"; // Use const or read-only to make a variable immutable // const values are calculated at compile time const int HoursWorkPerWeek = 9001; /////////////////////////////////////////////////// // Data Structures /////////////////////////////////////////////////// // Arrays - zero indexed // The array size must be decided upon declaration // The format for declaring an array is follows: // <datatype>[] <var name> = new <datatype>[<array size>]; int[] intArray = new int[10]; // Another way to declare & initialize an array int[] y = { 9000, 1000, 1337 }; // Indexing an array - Accessing an element Console.WriteLine("intArray @ 0: " + intArray[0]); // Arrays are mutable. intArray[1] = 1; // Lists // Lists are used more frequently than arrays as they are more flexible // The format for declaring a list is follows: // List<datatype> <var name> = new List<datatype>(); List<int> intList = new List<int>(); List<string> stringList = new List<string>(); List<int> z = new List<int> { 9000, 1000, 1337 }; // intialize // The <> are for generics - Check out the cool stuff section // Lists don't default to a value; // A value must be added before accessing the index intList.Add(1); Console.WriteLine("intList @ 0: " + intList[0]); // Others data structures to check out: // Stack/Queue // Dictionary (an implementation of a hash map) // HashSet // Read-only Collections // Tuple (.Net 4+) /////////////////////////////////////// // Operators /////////////////////////////////////// Console.WriteLine(" ->Operators"); int i1 = 1, i2 = 2; // Shorthand for multiple declarations // Arithmetic is straightforward Console.WriteLine(i1 + i2 - i1 * 3 / 7); // => 3 // Modulo Console.WriteLine("11%3 = " + (11 % 3)); // => 2 // Comparison operators Console.WriteLine("3 == 2? " + (3 == 2)); // => false Console.WriteLine("3 != 2? " + (3 != 2)); // => true Console.WriteLine("3 > 2? " + (3 > 2)); // => true Console.WriteLine("3 < 2? " + (3 < 2)); // => false Console.WriteLine("2 <= 2? " + (2 <= 2)); // => true Console.WriteLine("2 >= 2? " + (2 >= 2)); // => true // Bitwise operators! /* ~ Unary bitwise complement << Signed left shift >> Signed right shift & Bitwise AND ^ Bitwise exclusive OR | Bitwise inclusive OR */ // Incrementations int i = 0; Console.WriteLine(" ->Inc/Dec-rementation"); Console.WriteLine(i++); //i = 1. Post-Incrementation Console.WriteLine(++i); //i = 2. Pre-Incrementation Console.WriteLine(i--); //i = 1. Post-Decrementation Console.WriteLine(--i); //i = 0. Pre-Decrementation /////////////////////////////////////// // Control Structures /////////////////////////////////////// Console.WriteLine(" ->Control Structures"); // If statements are c-like int j = 10; if (j == 10) { Console.WriteLine("I get printed"); } else if (j > 10) { Console.WriteLine("I don't"); } else { Console.WriteLine("I also don't"); } // Ternary operators // A simple if/else can be written as follows // <condition> ? <true> : <false> string isTrue = (true) ? "True" : "False"; // While loop int fooWhile = 0; while (fooWhile < 100) { //Iterated 100 times, fooWhile 0->99 fooWhile++; } // Do While Loop int fooDoWhile = 0; do { // Start iteration 100 times, fooDoWhile 0->99 if (false) continue; // skip the current iteration fooDoWhile++; if (fooDoWhile == 50) break; // breaks from the loop completely } while (fooDoWhile < 100); //for loop structure => for(<start_statement>; <conditional>; <step>) for (int fooFor = 0; fooFor < 10; fooFor++) { //Iterated 10 times, fooFor 0->9 } // For Each Loop // foreach loop structure => foreach(<iteratorType> <iteratorName> in <enumerable>) // The foreach loop loops over any object implementing IEnumerable or IEnumerable<T> // All the collection types (Array, List, Dictionary...) in the .Net framework // implement one or both of these interfaces. // (The ToCharArray() could be removed, because a string also implements IEnumerable) foreach (char character in "Hello World".ToCharArray()) { //Iterated over all the characters in the string } // Switch Case // A switch works with the byte, short, char, and int data types. // It also works with enumerated types (discussed in Enum Types), // the String class, and a few special classes that wrap // primitive types: Character, Byte, Short, and Integer. int month = 3; string monthString; switch (month) { case 1: monthString = "January"; break; case 2: monthString = "February"; break; case 3: monthString = "March"; break; // You can assign more than one case to an action // But you can't add an action without a break before another case // (if you want to do this, you would have to explicitly add a goto case x case 6: case 7: case 8: monthString = "Summer time!!"; break; default: monthString = "Some other month"; break; } /////////////////////////////////////// // Converting Data Types And Typecasting /////////////////////////////////////// // Converting data // Convert String To Integer // this will throw a FormatException on failure int.Parse("123");//returns an integer version of "123" // try parse will default to type default on failure // in this case: 0 int tryInt; if (int.TryParse("123", out tryInt)) // Function is boolean Console.WriteLine(tryInt); // 123 // Convert Integer To String // Convert class has a number of methods to facilitate conversions Convert.ToString(123); // or tryInt.ToString(); // Casting // Cast decimal 15 to a int // and then implicitly cast to long long x = (int) 15M; } /////////////////////////////////////// // CLASSES - see definitions at end of file /////////////////////////////////////// public static void Classes() { // See Declaration of objects at end of file // Use new to instantiate a class Bicycle trek = new Bicycle(); // Call object methods trek.SpeedUp(3); // You should always use setter and getter methods trek.Cadence = 100; // ToString is a convention to display the value of this Object. Console.WriteLine("trek info: " + trek.Info()); // Instantiate a new Penny Farthing PennyFarthing funbike = new PennyFarthing(1, 10); Console.WriteLine("funbike info: " + funbike.Info()); Console.Read(); } // End main method // CONSOLE ENTRY A console application must have a main method as an entry point public static void Main(string[] args) { OtherInterestingFeatures(); } // // INTERESTING FEATURES // // DEFAULT METHOD SIGNATURES public // Visibility static // Allows for direct call on class without object int // Return Type, MethodSignatures( int maxCount, // First variable, expects an int int count = 0, // will default the value to 0 if not passed in int another = 3, params string[] otherParams // captures all other parameters passed to method ) { return -1; } // Methods can have the same name, as long as the signature is unique // A method that differs only in return type is not unique public static void MethodSignatures( ref int maxCount, // Pass by reference out int count) { count = 15; // out param must be assigned before control leaves the method } // GENERICS // The classes for TKey and TValue is specified by the user calling this function. // This method emulates the SetDefault of Python public static TValue SetDefault<TKey, TValue>( IDictionary<TKey, TValue> dictionary, TKey key, TValue defaultItem) { TValue result; if (!dictionary.TryGetValue(key, out result)) return dictionary[key] = defaultItem; return result; } // You can narrow down the objects that are passed in public static void IterateAndPrint<T>(T toPrint) where T: IEnumerable<int> { // We can iterate, since T is a IEnumerable foreach (var item in toPrint) // Item is an int Console.WriteLine(item.ToString()); } public static void OtherInterestingFeatures() { // OPTIONAL PARAMETERS MethodSignatures(3, 1, 3, "Some", "Extra", "Strings"); MethodSignatures(3, another: 3); // explicity set a parameter, skipping optional ones // BY REF AND OUT PARAMETERS int maxCount = 0, count; // ref params must have value MethodSignatures(ref maxCount, out count); // EXTENSION METHODS int i = 3; i.Print(); // Defined below // NULLABLE TYPES - great for database interaction / return values // any value type (i.e. not a class) can be made nullable by suffixing a ? // <type>? <var name> = <value> int? nullable = null; // short hand for Nullable<int> Console.WriteLine("Nullable variable: " + nullable); bool hasValue = nullable.HasValue; // true if not null // ?? is syntactic sugar for specifying default value (coalesce) // in case variable is null int notNullable = nullable ?? 0; // 0 // IMPLICITLY TYPED VARIABLES - you can let the compiler work out what the type is: var magic = "magic is a string, at compile time, so you still get type safety"; // magic = 9; will not work as magic is a string, not an int // GENERICS // var phonebook = new Dictionary<string, string>() { {"Sarah", "212 555 5555"} // Add some entries to the phone book }; // Calling SETDEFAULT defined as a generic above Console.WriteLine(SetDefault<string,string>(phonebook, "Shaun", "No Phone")); // No Phone // nb, you don't need to specify the TKey and TValue since they can be // derived implicitly Console.WriteLine(SetDefault(phonebook, "Sarah", "No Phone")); // 212 555 5555 // LAMBDA EXPRESSIONS - allow you to write code in line Func<int, int> square = (x) => x * x; // Last T item is the return value Console.WriteLine(square(3)); // 9 // ERROR HANDLING - coping with an uncertain world try { var funBike = PennyFarthing.CreateWithGears(6); // will no longer execute because CreateWithGears throws an exception string some = ""; if (true) some = null; some.ToLower(); // throws a NullReferenceException } catch (NotSupportedException) { Console.WriteLine("Not so much fun now!"); } catch (Exception ex) // catch all other exceptions { throw new ApplicationException("It hit the fan", ex); // throw; // A rethrow that preserves the callstack } // catch { } // catch-all without capturing the Exception finally { // executes after try or catch } // DISPOSABLE RESOURCES MANAGEMENT - let you handle unmanaged resources easily. // Most of objects that access unmanaged resources (file handle, device contexts, etc.) // implement the IDisposable interface. The using statement takes care of // cleaning those IDisposable objects for you. using (StreamWriter writer = new StreamWriter("log.txt")) { writer.WriteLine("Nothing suspicious here"); // At the end of scope, resources will be released. // Even if an exception is thrown. } // PARALLEL FRAMEWORK // http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx var websites = new string[] { "http://www.google.com", "http://www.reddit.com", "http://www.shaunmccarthy.com" }; var responses = new Dictionary<string, string>(); // Will spin up separate threads for each request, and join on them // before going to the next step! Parallel.ForEach(websites, new ParallelOptions() {MaxDegreeOfParallelism = 3}, // max of 3 threads website => { // Do something that takes a long time on the file using (var r = WebRequest.Create(new Uri(website)).GetResponse()) { responses[website] = r.ContentType; } }); // This won't happen till after all requests have been completed foreach (var key in responses.Keys) Console.WriteLine("{0}:{1}", key, responses[key]); // DYNAMIC OBJECTS (great for working with other languages) dynamic student = new ExpandoObject(); student.FirstName = "First Name"; // No need to define class first! // You can even add methods (returns a string, and takes in a string) student.Introduce = new Func<string, string>( (introduceTo) => string.Format("Hey {0}, this is {1}", student.FirstName, introduceTo)); Console.WriteLine(student.Introduce("Beth")); // IQUERYABLE<T> - almost all collections implement this, which gives you a lot of // very useful Map / Filter / Reduce style methods var bikes = new List<Bicycle>(); bikes.Sort(); // Sorts the array bikes.Sort((b1, b2) => b1.Wheels.CompareTo(b2.Wheels)); // Sorts based on wheels var result = bikes .Where(b => b.Wheels > 3) // Filters - chainable (returns IQueryable of previous type) .Where(b => b.IsBroken && b.HasTassles) .Select(b => b.ToString()); // Map - we only this selects, so result is a IQueryable<string> var sum = bikes.Sum(b => b.Wheels); // Reduce - sums all the wheels in the collection // Create a list of IMPLICIT objects based on some parameters of the bike var bikeSummaries = bikes.Select(b=>new { Name = b.Name, IsAwesome = !b.IsBroken && b.HasTassles }); // Hard to show here, but you get type ahead completion since the compiler can implicitly work // out the types above! foreach (var bikeSummary in bikeSummaries.Where(b => b.IsAwesome)) Console.WriteLine(bikeSummary.Name); // ASPARALLEL // And this is where things get wicked - combines linq and parallel operations var threeWheelers = bikes.AsParallel().Where(b => b.Wheels == 3).Select(b => b.Name); // this will happen in parallel! Threads will automagically be spun up and the // results divvied amongst them! Amazing for large datasets when you have lots of // cores // LINQ - maps a store to IQueryable<T> objects, with delayed execution // e.g. LinqToSql - maps to a database, LinqToXml maps to an xml document var db = new BikeRepository(); // execution is delayed, which is great when querying a database var filter = db.Bikes.Where(b => b.HasTassles); // no query run if (42 > 6) // You can keep adding filters, even conditionally - great for "advanced search" functionality filter = filter.Where(b => b.IsBroken); // no query run var query = filter .OrderBy(b => b.Wheels) .ThenBy(b => b.Name) .Select(b => b.Name); // still no query run // Now the query runs, but opens a reader, so only populates are you iterate through foreach (string bike in query) Console.WriteLine(result); } } // End LearnCSharp class // You can include other classes in a .cs file public static class Extensions { // EXTENSION FUNCTIONS public static void Print(this object obj) { Console.WriteLine(obj.ToString()); } } // Class Declaration Syntax: // <public/private/protected/internal> class <class name>{ // //data fields, constructors, functions all inside. // //functions are called as methods in Java. // } public class Bicycle { // Bicycle's Fields/Variables public int Cadence // Public: Can be accessed from anywhere { get // get - define a method to retrieve the property { return _cadence; } set // set - define a method to set a proprety { _cadence = value; // Value is the value passed in to the setter } } private int _cadence; protected virtual int Gear // Protected: Accessible from the class and subclasses { get; // creates an auto property so you don't need a member field set; } internal int Wheels // Internal: Accessible from within the assembly { get; private set; // You can set modifiers on the get/set methods } int _speed; // Everything is private by default: Only accessible from within this class. // can also use keyword private public string Name { get; set; } // Enum is a value type that consists of a set of named constants // It is really just mapping a name to a value (an int, unless specified otherwise). // The approved types for an enum are byte, sbyte, short, ushort, int, uint, long, or ulong. // An enum can't contain the same value twice. public enum BikeBrand { AIST, BMC, Electra = 42, //you can explicitly set a value to a name Gitane // 43 } // We defined this type inside a Bicycle class, so it is a nested type // Code outside of this class should reference this type as Bicycle.Brand public BikeBrand Brand; // After declaring an enum type, we can declare the field of this type // Decorate an enum with the FlagsAttribute to indicate that multiple values can be switched on [Flags] // Any class derived from Attribute can be used to decorate types, methods, parameters etc public enum BikeAccessories { None = 0, Bell = 1, MudGuards = 2, // need to set the values manually! Racks = 4, Lights = 8, FullPackage = Bell | MudGuards | Racks | Lights } // Usage: aBike.Accessories.HasFlag(Bicycle.BikeAccessories.Bell) // Before .NET 4: (aBike.Accessories & Bicycle.BikeAccessories.Bell) == Bicycle.BikeAccessories.Bell public BikeAccessories Accessories { get; set; } // Static members belong to the type itself rather then specific object. // You can access them without a reference to any object: // Console.WriteLine("Bicycles created: " + Bicycle.bicyclesCreated); public static int BicyclesCreated { get; set; } // readonly values are set at run time // they can only be assigned upon declaration or in a constructor readonly bool _hasCardsInSpokes = false; // read-only private // Constructors are a way of creating classes // This is a default constructor public Bicycle() { this.Gear = 1; // you can access members of the object with the keyword this Cadence = 50; // but you don't always need it _speed = 5; Name = "Bontrager"; Brand = BikeBrand.AIST; BicyclesCreated++; } // This is a specified constructor (it contains arguments) public Bicycle(int startCadence, int startSpeed, int startGear, string name, bool hasCardsInSpokes, BikeBrand brand) : base() // calls base first { Gear = startGear; Cadence = startCadence; _speed = startSpeed; Name = name; _hasCardsInSpokes = hasCardsInSpokes; Brand = brand; } // Constructors can be chained public Bicycle(int startCadence, int startSpeed, BikeBrand brand) : this(startCadence, startSpeed, 0, "big wheels", true, brand) { } // Function Syntax: // <public/private/protected> <return type> <function name>(<args>) // classes can implement getters and setters for their fields // or they can implement properties (this is the preferred way in C#) // Method parameters can have default values. // In this case, methods can be called with these parameters omitted public void SpeedUp(int increment = 1) { _speed += increment; } public void SlowDown(int decrement = 1) { _speed -= decrement; } // properties get/set values // when only data needs to be accessed, consider using properties. // properties may have either get or set, or both private bool _hasTassles; // private variable public bool HasTassles // public accessor { get { return _hasTassles; } set { _hasTassles = value; } } // You can also define an automatic property in one line // this syntax will create a backing field automatically. // You can set an access modifier on either the getter or the setter (or both) // to restrict its access: public bool IsBroken { get; private set; } // Properties can be auto-implemented public int FrameSize { get; // you are able to specify access modifiers for either get or set // this means only Bicycle class can call set on Framesize private set; } // It's also possible to define custom Indexers on objects. // All though this is not entirely useful in this example, you // could do bicycle[0] which yields "chris" to get the first passenger or // bicycle[1] = "lisa" to set the passenger. (of this apparent quattrocycle) private string[] passengers = { "chris", "phil", "darren", "regina" }; public string this[int i] { get { return passengers[i]; } set { return passengers[i] = value; } } //Method to display the attribute values of this Object. public virtual string Info() { return "Gear: " + Gear + " Cadence: " + Cadence + " Speed: " + _speed + " Name: " + Name + " Cards in Spokes: " + (_hasCardsInSpokes ? "yes" : "no") + " ------------------------------ " ; } // Methods can also be static. It can be useful for helper methods public static bool DidWeCreateEnoughBycles() { // Within a static method, we only can reference static class members return BicyclesCreated > 9000; } // If your class only needs static members, consider marking the class itself as static. } // end class Bicycle // PennyFarthing is a subclass of Bicycle class PennyFarthing : Bicycle { // (Penny Farthings are those bicycles with the big front wheel. // They have no gears.) // calling parent constructor public PennyFarthing(int startCadence, int startSpeed) : base(startCadence, startSpeed, 0, "PennyFarthing", true, BikeBrand.Electra) { } protected override int Gear { get { return 0; } set { throw new InvalidOperationException("You can't change gears on a PennyFarthing"); } } public static PennyFarthing CreateWithGears(int gears) { var penny = new PennyFarthing(1, 1); penny.Gear = gears; // Oops, can't do this! return penny; } public override string Info() { string result = "PennyFarthing bicycle "; result += base.ToString(); // Calling the base version of the method return result; } } // Interfaces only contain signatures of the members, without the implementation. interface IJumpable { void Jump(int meters); // all interface members are implicitly public } interface IBreakable { bool Broken { get; } // interfaces can contain properties as well as methods & events } // Class can inherit only one other class, but can implement any amount of interfaces class MountainBike : Bicycle, IJumpable, IBreakable { int damage = 0; public void Jump(int meters) { damage += meters; } public bool Broken { get { return damage > 100; } } } /// <summary> /// Used to connect to DB for LinqToSql example. /// EntityFramework Code First is awesome (similar to Ruby's ActiveRecord, but bidirectional) /// http://msdn.microsoft.com/en-us/data/jj193542.aspx /// </summary> public class BikeRepository : DbContext { public BikeRepository() : base() { } public DbSet<Bicycle> Bikes { get; set; } } } // End Namespace