Brief Introduction To C# The Native Language Of

COMPSCI 711C# 1.2radu/2009Brief introduction to C# – the native language of .NETo C# Language Specifications, 4th Edition, Standard ECMA-334, 2006, Ch 8 – Language ions/standards/Ecma-334.htmo CSharp Language Specification, Version 3.0, 2007, Ch 1 – p/aa336809.aspxCompiling from the command-lineo We need csc on the patho We can also call vsvars32.batAssembly .NET executable binary: .EXE or .DLLEx: mscorlib.dll, System.Windows.Forms.dllSET PATH llCompilers (csc) and Tools (VS) aretypically configured to automaticallyreference several ―core‖ libraries, suchas mscorlib.dllhello.csLinqPadA great 3rd party free interactivetesting tool1.13

COMPSCI 711C# 1.2radu/2009Type system unificationAll types—including value types—derive from the root type object (in one or more steps)7.ToString();// Value types and reference typesThe different meanings of B AReference type : one balloon, two handles Value typeobjectboxingunboxingA: 7B: 7ABo An int value can be converted (actually copied) to an object (boxing)o and back again to int (unboxing).object o i;// implicit boxing, by copyint j (int) o;// explicit unboxing, by copyUsed carefully, boxing provides object-ness, without introducing unnecessary overhead (careful).2.13

COMPSCI 711C# 1.2radu/2009Boxing in Classic Collectionspublic class Stack {public void Push(object o){. }public object Pop(){. }}Stack stack new Stack();stack.Push(12);int i (int)stack.Pop();Safe type-castfor reference typesstring s s stack.Pop()stack.Pop()asasstring;string;o What if the top is not an int?o Exception! needs a try blocko or a safe typecasto s null if cast is not possibleo sNo nullif cast is not possibleexception!No exception!Generic Collectionspublic class Stack T {public void Push(T o){. }public T Pop(){. }}Stack int stack new Stack int ();stack.Push(12);int i stack.Pop(); // conversion not neededAdvantageso Static type safetyo PerformanceLater we’ll talk a bit more about generictypes and methods3.13

COMPSCI 711C# 1.2radu/2009Reference parameters – the values of corresponding variables may changestatic void Swap(ref int a, ref int b) {int t a;a b;pre:x 1, y 2b t;post:x 2, y 1}int x 1; int y 2;Console.WriteLine("pre: x {0}, y {1}", x, y);Swap(ref x, ref y);Console.WriteLine("post: x {0}, y {1}", x, y);An output parameter – like a ref parameter, but the initial value is unimportantstatic void Divide(int a, int b,out int quotient, out int remainder) {quotient a / b;remainder a % b;}int i 5, j 2, q, r ;Divide(i, j, out q, out r);Console.WriteLine("{0} / {1} {2} rest {3}",i, j, q, r);5 / 2 2 rest 14.13

COMPSCI 711C# 1.2radu/2009A parameter array represents a variable length argument list.static void F(params int[] args) {Console.WriteLine("# of arguments: {0}", args.Length);for (int i 0; i args.Length; i )Console.WriteLine("\targs[{0}] {1}", i, args[i]);}// could also use foreach, as belowF( );F(1);F(1, 2);F(1, 2, 3);F(new int[] {1, 2, 3, 4});foreach statementso foreach can be applied to any array, collection, or stringo in fact to any object that implements IEnumerable or IEnumerable T – i.e., to sequenceso foreach statements make life easier for users such sequenceso we’ll see later how iterators simplify the task of sequence developersint[] args ;ArrayList args ;foreach (int a in args) {Console.WriteLine(a);}IEnumerator myEnumerator args.GetEnumerator();while (myEnumerator.MoveNext()) {int a (int) myEnumerator.Current;Console.WriteLine(a);}5.13

COMPSCI 711C# 1.2radu/2009PropertiesProperties extend fields. However, instead of defining storage locations, properties have get andset accessors that specify the statements to be executed when their values are read or written.public class Button { // simplifiedprivate string caption;public string Caption {get {return caption;}set {caption value;Repaint();}}}Button b new Button();b.Caption "ABC";// set; causes repaintstring s b.Caption;// getb.Caption "DEF";// get & set; causes repaintthe same in old Java-like styleb.setCaption( b.getCaption() ―DEF‖ );which one is more readable?6.13

COMPSCI 711C# 1.2radu/2009Indexers – look like associative arraysAn indexer is a property extended with parameters, that enables an object to be indexed like an array– and its ―indices‖ can be not only integers, but also strings or any other object type.// Sample usage:public class Vector { // simplifiedVector v new Vector();public object this[int index] {v[0] 10;// setget {// setif (! ValidIndex(index)) throw v[1] 11;int i v[1];// getelse return some value v[1] 2;// get & set}// Traditional usageset {v.set ElementAt(2, v.get ElementAt(2); 2);if (! ValidIndex(index)) throw else store some value }A collection example: Dictionary TKey, TValue generic class}Maps key objects, typically strings object values.Indexers can be overloaded, e.g.,}Dictionary string, string openWith new Dictionary string, string ();public object this[string index] { }openWith["rtf"] "winword.exe";7.13

COMPSCI 711C# 1.2radu/2009Struct’s (structures)Similar to classes but more ―light-weight‖:o struct’s are value types rather than reference typeso inheritance is not supported for struct’so struct values are stored ―on the stack‖ or ―in-line‖o struct values are copied on assignment ( )o careful use may enhance performance.struct Point {public int x, y;public Point(int x, int y) {this.x x;this.y y;}}Point p, q;p new Point(10, 20);q p;q.x 30;o check the last values of p and qo what will happen if Point were a class8.13

COMPSCI 711C# 1.2radu/2009Delegateso Delegates are object-oriented, type-safe, and secure function pointers that encapsulates one ormore methods (multicast), together with their associated instance or class.{ (instance, method on that instance), (class, method on that class), }.delegate void SimpleDelegate();// matches both S and I belowclass Test {public static void S() { }public void I() { }}As we will see later, methodscan also be defined on-the-fly,via anonymous delegates orlambda expressions.SimpleDelegate d;d new SimpleDelegate(Test.S);d Test.S;d();// or// since C# 2.0// calls Test.S()// SimpleDelegate d;Test t new Test();d t.I;d();// calls t.I()// SimpleDelegate d;d Test.S; d t.I;d();// calls Test.S() and t.I()9.13

COMPSCI 711C# 1.2radu/2009Eventso An event is a member of a delegate type that enables an object or class to provide notifications.o Only and - are available from outside (why?).public delegate void EventHandler(object sender,System.EventArgs e);// System definitionpublic class Button { // simplifiedpublic event EventHandler Click;public void Reset() {Click null;}// somewhere we fire the event// and this will broadcast it// to all registered handlers, if anyif (Click ! null) Click( , );}public class Form1: Form {Button Button1 new Button();public void Form1() {Button1.Click Button1 Click1;Button1.Click Button1 Click2;}void Button1 Click1(object sender, EventArgs e) {Console.WriteLine("Button1 was clicked (1)!");}void Button1 Click2(object sender, EventArgs e) {Console.WriteLine("Button1 was clicked (2)!");}What is executed? Considerpublic void Disconnect() { several scenarios.Button1.Click - Button1 Click2;}}10.13

COMPSCI 711C# 1.2radu/2009Attributeso To attach declarative information to various program entities, such as methods, fields and classes,and later retrieve and interpret this declarative information at run-time (using reflection)o ASP.NET, XML and most run-time environments rely heavily on specific system-defined attributes.Example: OperationContract Attribute (WCF, more later)System definition:public sealed class OperationContractAttribute : AttributeSample usage:[OperationContract()] AddToCart(object o) { }[OperationContract] AddToCart(object o) { }[OperationContract(IsOneWay true)] AddToCart(object o){ }Other examplesStructLayout To create union types (unavailable in the language)DllImportTo import ―legacy‖ DLLsObsoleteCompiler will complain if target is used11.13o Attribute usage is really objectinstantiation.o A crisp notation combiningconstructor call plus propertysetup, e.g.,OperationContractAttribute oc new OperationContractAttribute ();OperationContractAttribute oc new OperationContractAttribute ();oc.IsOneWay true;

COMPSCI 711Versioning, explicitvirtual chains,broken chainsC# 1.2radu/2009Solves the ―fragile base class‖ 336813.aspxhttp://www.cs.aau.dk/ e-fbc-problem.htmlclass A {public void f() { }}class A {public virtual void f() { }}class A {public virtual void f() { }}class B: A {public void f() { }}class B: A {public override void f() { }}class B: A {public override void f() { }}class C: B {public void f() { }}class C: B {public override void f() { }}class C: B {public new virtual void f() { }}A x new C();x.f(); //A.f()A x new C();x.f(); //C.f()A x new C();x.f(); //B.f()No implicit overriding!Warning w/o newExplicit overriding!Explicit virtual chain A-B-C.12.13Partial overriding!―Broken chain‖ between B and C(2 chains: A-B and C)

COMPSCI 711C# 1.2radu/2009Summary of the possibly most interesting new language features (C# version 1)Type system unification & boxing7.ToString(); stack.Push(12);Type-safe castingobj as PointRef/out parametersSwap(ref int a, ref int b)Params arraysF(1); F(1, 2); F(1, 2, 3);Foreach loopsforeach (string s in args) { }Propertiesint MyProp {get {return ;} set { }}Indexersint this[int index] {get {return ;} set { }}Structuresstruct Point {public int x, y;}Delegatesdelegate void SimpleDelegate();EventsButton1.Click Button1 Click1; //new EventHandler( )Attributes[OperationContract(IsOneWay true)]public bool AddToCart(object o)Versioning – explicit overridepublic virtual void f() { }public override void f() { }13.13

COMPSCI 711 C# 1.2 radu/2009 2.13 boxing o An int value can be converted (actually copied) to an object (boxing) o and back again to int (unboxing). object o i; // implicit boxing, by copy int j (int) o; // explicit unboxing, by copy Used carefully, boxing provides object-ness, without introducin