Chapter 1 Presentation

Chapter 1: Framework Fundamentals produced by BichTran

Objectives Manage data by using the .NET Framework 2.0 system types. Implement .NET Framework interfaces Control interactions between components by using events and delegates

Agenda Lesson 1: Using Value Types Lesson 2: Using Common Reference Types Lesson 3: Constructing Classes Lesson 4: Converting Between Types Question and answer Practice test

Using Value Types Built-in types : sbyte – byte – short – int – uint – float long –double – decimal char – bool – date – none (Pointer to a memory address) Enumerations : - enum User-defined types: - struct ( Operators is new in .NET 2.0) struct Cycle { int _val, _min, _max; public Cycle (int min, int max) { _val = min; _min = min; _max = max;} public static Cycle operator +(Cycle arg1, int arg2) { arg1.Value += arg2; return arg1; } public static Cycle operator -(Cycle arg1, int arg2) { arg1.Value -= arg2; return arg1;} }

Using Value Types (cont.) Use with new feature of Struct (operators) in .NET 2.0 Cycle degrees = new Cycle(0, 359); Cycle quarters = new Cycle(1, 4); for (int i = 0; i <= 8; i++) { degrees += 90; quarters += 1; Console.WriteLine("degrees = {0}, quarters = {1}", degrees, quarters); } In short, structure types is suitable for simple data, size less than 16 bytes, not be changed after creation, not be cast to a reference type Summary: Assigning value-type variables, the data is copied and stored on the stack. Value-types represent simple values, they have methods (as objects) The Nullable type is new in .NET 2.0. Case: use a variable as nullable when its value has not been assigned. Ex: a bool variable has not been assigned

Using Common Reference Types There are about 2500 built-in reference types in the .NET Framework (not derived from System. ValueType ): Object: the most general type, any type can be converted to Object. String and StringBuilder: StringBuilder is more flexible than String Exception : unexpected events that interrupt normal execution of an assembly. Use following blocks in case catching exceptions: try {} catch (Exception ex) {} finally {} Tips: - Your own exceptions will be derived from System.ApplicationException - The runtime will execute only the first Catch block matching exception type. So order of Catch blocks should be from the most-specific to the least-specific . ,etc.

Constructing Classes Inheritance: use inheritance to create new types based on existing ones. Interface: use interfaces to define a common set of members that must be implemented by related types. For example, the IComparable , IDisposable, IConvertible .etc. Partial class: use partial classes to split a class definition across multiple source files. Use: “ partial ”is preceded keyword “ class ” Generics (new in .NET 2.0) NET 1.0 and 1.1 did not support generics. With Generics Without Generics public class Gen<T, U> { public T t; public U u; public Gen(T _t, U _u) { t = _t; u = _u;} } public class Obj { public Object t; public Object u; public Obj(Object _t, Object _u) { t = _t; u = _u; } }

Constructing Classes (cont.) With Generics Without Generics Gen<string, string> ga = new Gen<string, string>("Hello, ", "World!"); string s = ga.t + ga.u; Gen<double, int> gb = new Gen<double, int>(10.125, 2005); double db = gb.t + gb.u; Obj oa = new Obj("Hello, ", "World!"); string s = (string)oa.t + (string)oa.u); Obj ob = new Obj(10.125, 2005); double db = (double)ob.t + (int)ob.u); double db = (int)ob.t + (int)ob.u); // runtime exception

Constructing Classes (cont.) Event: An event is a message sent by an object to signal the occurrence of an action. Delegate : A delegate is a class that can hold references to a methods which matches its signature. ( like method-pointer) public event MyEventHandler MyEvent; public delegate void MyEventHandler(object sender, EventArgs e); Raise event : MyEventHandler handler = MyEvent; EventArgs e = new EventArgs(); if (handler != null) { // Invokes the delegates. handler(this, e); } //C# checks to determine whether handler is null. Respond to the event: private void button1_Click(object sender, EventArgs e) {} button1.Click += new System.EventHandler(this.button1_Click);

Constructing Classes (cont.) Attributes: Use attributes to describe assemblies, types, and members. For example : [Serializable] class ShoppingCartItem {….} Type Forwarding (thinking) Using attribute “TypeForwardedTo” to move a type from one class library to another using System.Runtime.CompilerServices; [assembly:TypeForwardedTo(typeof(DestLib.TypeA))]

Converting Between Types Conversion: 2 kinds Widening Conversion : the range of the destination type is wider than that of the source type.(implicit conversion) Narrowing conversion: the range or precision of the source type exceeds that of the destination type, which usually requires explicit conversion. NOTE : Use TryParse, TryParseExact, and TryCast are new in .NET 2.0. Instead of attempting a parsing/conversion and catch the exception if it failed. Boxing and Unboxing Boxing converts a value type to a reference type. Unboxing converts a reference type to a value type. Unboxing Boxing object o = 123; int i = (int) o; int i = 123; object o = (object) i;

Chapter 1 Presentation

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Chapter 1 Presentation