Introduction to .NET Framework

1

• Introduction to .NET Framework
• Gholamali Semsarzadeh
• July 2001

2
What Is .NET

• .Net is a new framework for developing
  windows-based and web-based applications within
  the Microsoft environment.
• The framework offers a new set of software
  development tools that are superior to the old
  tools.
• The framework offers a fundamental shift in
  Microsoft strategy it moves application
  development from client-centric to
  server-centric.

3
Agenda

• Common language runtime (CLR)
• .NET class library
• Cross language application development
• Tools for developing Windows applications
• Tools for developing Web applications

4
Common Language Runtime (CLR)

• CLR works like a virtual machine in executing all
  languages. Currently it supports two
• C is the new version of C containing all
  features of Java.
• VB.NET is the new version of VB containing full
  object orientation and equal in power to C.
• All .NET languages must obey the rules and
  standards imposed by CLR. Examples
• Object declaration, creation and use
• Data types,language libraries
• Error and exception handling
• Interactive Development Environment (IDE)

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Intermediate Language (IL)

• .NET languages are not compiled to machine code.
  They are compiled to an Intermediate Language
  (IL).
• CLR accepts the IL code and recompiles it to
  machine code. The recompilation is just-in-time
  (JIT) meaning it is done as soon as a function or
  subroutine is called.
• The JIT code stays in memory for subsequent
  calls. In cases where there is not enough memory
  it is discarded thus making JIT process
  interpretive.

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Common Data Types

• CLR provides a set of primitive types that all
  languages must support. The data types include
• Integerthree types 16/32/64 bits
• Floattwo types 32/64 bits
• Boolean and Character
• Date/time and Time span
• The primitive types can be collected into
• Arrays
• Structures
• Combination of the two

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Common Type System

• IL is completely object-oriented. It requires
  everything to be the type of a class, structure
  or interface.
• Examples of types
• Integer
• String
• Rectangle
• Customer
• Contract
• Chart
• Recordset
• Check
• Financial Institution

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Examples of Types
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Metadata

• A type must be self descriptive It must
  describe properties and methods that it exposes.
• Examples
• The type Integer describes what values it takes
  and what operations it accepts.
• The type Check describes what values (e.g.,
  AccountNo and Amount) it takes and what
  operations (e.g., Cash, Deposit) it accepts.
• The Metadata is an integral part of an executable
  such as CHART.DLL. The DLL describes two things
  about the Chart type what it does and how it
  does it.

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Assembly

• To allow others to use a type, the developer must
  package it in an assembly.
• A component (delivered in an assembly) is the
  building block for software construction.
• Structurally an assembly consists of a manifest
  and one or more modules. Each module consists of
  metadata (in IDL) and one or more types (in IL).

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Manifest

• The manifest identifies an assembly and declares
  its contents.
• It describes
• Identity of an assembly
• Its security requirements
• The identity of other assemblies it depends on
• The types exposed by the assembly

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.NET Class Library

• In traditional environments different categories
  of services are provided to the programmer via
  libraries such as C run time library, Win32
  APIs, I/O and database access libraries,
  statistical libraries, etc.
• These libraries are language dependent, operating
  system dependent, and often contain simple
  subroutine calls as opposed to self describing
  types.
• In .NET all services fall into a single,
  hierarchy organized, language independent Class
  Library.

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.NET Class Library 2

• The organization of the Class Library is similar
  to the file system
• Each folder is a NameSpace
• Each file is an assembly exposing one or more
  types
• The root of the Class Library is the System
  NameSpace
• The Class Library contains 25 second level
  NameSpaces such as Data, I/O, WinForms, Security,
  etc. that contain thousands of types exposing all
  services of the operating system.
• All components developed by the users or vendors
  must be added to the Class Library before they
  can be used.

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VB.NET

• The .NET version of Visual Basic is as powerful
  as C and is incompatible with its previous
  version VB 6.0.
• It contains the following new features all of
  which are enforced by CLR and are common with C
• Common IDE (Interactive Development Environment)
• Common type system
• Common object orientation capabilities
• Common language library
• Common error and exception handling
• Common form drawing tools
• Common Web page design tools

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The OBJECT Class

• OBJECT is the type from which all other types are
  derived.
• The properties and methods that are shared by all
  objects are constructed in the OBJECT class.
  They include
• Equals
• GetType
• Clone (duplicate)
• GetHashCode
• ToString
• The OBJECT type in VB.NET replaces the VARIANT
  type in previous versions of VB.

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Visual Basic Form as a Class

• All .NET languages use the same tools (WinForms)
  to create the user interface of an application as
  a form.
• A form a class containing other classes (called
  controls) such as TextBox, ListBox or Button.
• The act of drawing a form (such as Form1)
  generates the VB.NET code that defines the
  corresponding class named Form1.
• As a class, Form1 has methods, properties, and
  events. Examples
• Form1.Show is a method that displays the Form1 on
  the screen.
• Form1.EmpName.Text references the contents of the
  TextBox EmpName in Form1.
• EmpName_Change is the name of the event handler
  that is invoked when the user changes contents of
  EmpName TextBox.

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Inheritance Hierarchy of a Form

• The following hierarchy shows how the Visual
  Basic Form Class is derived from the Object
  class.
• Object The base class for everything
• RefObject Objects called by reference
• Component RefObjects that can be reused
• Control components with visual interface
• RichControl controls with advanced visual
  presentation such as color, font, docking
  capability
• ScrollableControl controls that can be scrolled
• ContainerControl Controls that can hold other
  controls and change focus among them
• Form Base Form class from which application
  specific forms are derived

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Inheriting From User Forms

• The class Form is located in the NameSpace
  System.WinForms.
• The act of drawing a form (Form1) in the IDE
  generates VB code containing the following
  declarations
• Imports System.WinForms
• Public Class Form1 Inherits Form
• The user then adds additional controls and code
  to Form1. Form1 can now be used as the base
  class for Form2 using the following declaration
• Imports System.WinForms
• Public Class Form2 Inherits Form1

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Visual Basic and WebForms

• In a manner similar to drawing a WinForm, the VB
  programmer can now draw a WebForm (I.e., a Web
  Page)and attach event handlers to it.
• WinForm controls such as Text, Image, and Anchor
  are similar to WinForm controls.
• A Web page, just like a form, is a class with its
  own methods, properties and events. It can be
  inherited by other Web pages.
• VB can thus be used to develop Web-based
  applications.

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Visual Basic and Web Services

• A Web Service a class (running on a Web Server)
  whose one or more methods are designated as
  WebMethods.
• A WebMethod can be called from any client across
  the Internet.
• The protocol for exchange of information is
  called SOAP (Simple Object Activation Protocol).
  It wraps the calling sequence in XML, invokes the
  remotely located method, and returns the computed
  results in XML.
• DCOM distributes logic over tightly connected
  nodes on a LAN. SOAP distributes logic over
  nodes that are loosely connected across the
  Internet.

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Web Applications in .NET

• The central question in creation of Web pages is
  weather an HTML markup is instruction or data
• lthtmlgtltbodygt
• ltpgtThis is some text.lt/pgt
• lt/bodygtlt/htmlgt
• The perspective varies depending on whether or
  not we are using
• HTML or DHTML to respond to user inputs
• ASP (or JSP) to generate HTML markups
• No matter how the Web page is generated the code
  behind it is very ad-hoc and non-structured. In
  the .NET platform, ASP.NET attempts to solve some
  of these problems.

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Server-Side Controls

• ASP and JSP provide a language to generate HTML
  markups. In ASP.NET the complexity of this
  language is significantly reduced by using
  server-side controls.
• For each HTML control (such as a list box or an
  input text box) there exists a server-side
  control in ASP.NET. When a Browser requests a
  specific ASP.NET page in its URL the following
  events happen
• The ASP.NET program is executed
• Each server-side control in that program
  generates a corresponding HTML control
• As the final result, the ASP.NET program
  generates an HTML page that is targeted to the
  version of the Browser that requested the page.

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ExampleServer-Side Controls

• ASP.NET code for displaying a listbox
• ltASPListBox IDList1 RUNATServergt
• ltASPListItemgtJanlt/ASPListItemgt
• ltASPListItemgtFeblt/ASPListItemgt
• ltASPListItemgtMarlt/ASPListItemgt
• lt/ASPListBoxgt
• Corresponding HTML code
• ltSELECT Size3gt
• ltOptiongtJanlt/Optiongt
• ltOptiongtFeblt/Optiongt
• ltOptiongtMarlt/Optiongt
• lt/SELECTgt

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Server-Side Processing

• A server-side control can detect a user event
  (e.g., a mouse click) and execute a server-side
  script that contains the code (the event handler)
  to handle that event.
• The event is generated on the client-side but
  handled on the server-side.
• The event handler typically changes the
  properties and calls the methods of various
  controls on the ASP.NET page.
• At the termination of the event handler a new
  HTML page is posted back to the Browser.

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Example Server-Side Processing

• lt_at_ import Namespacesystem.data gt
• lt_at_ import Namespacesystem.data.SQL gt
• lthtmlgt
• ltheadgtltScript LANGUAGEVB, RUNATServer gt
• Sub Page-load( )
• Dim SqlCmd As NEW SQLDataSetCOmmand (
• ServerlocalhostdatabaseBooks,
• select from Authors )
• Dim ds As New DataSet
• SqlCmd.FillDataSet(ds, Authors)
• Grid1.DataSourceds.Tables(Authors).Defaul
  tView
• Grid1.DataBind
• End Sub
• lt/Scriptgt
• lt/headgt
• ltbodygt
• ltASPDataGrid IDGrid1 RUNATServer /gt
• lt/bodygtlt/htmlgt

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ASP.NET Benefits

• ASP.NET Uses .NET languages to generate HTML
  pages. HTML page is targeted to the capabilities
  of the requesting Browser
• ASP.NET Program is compiled into a .NET class
  and cached the first time it is called. All
  subsequent calls use the cached version.
• ASP.NET programs are developed using the same
  IDE tools as VB Programs. There are however two
  important differences
• The code behind the controls is executed on the
  server
• The Web application does not need the CLR or the
  .NET Class Library to executeany Browser will do.