Introduction to ,NET Framework

Introduction to .NET
By Anurag Singh

What is .NET?
• Microsoft’s vision of the future of
applications in the Internet age
– Increased robustness over classic Windows
apps
– New programming platform
– Built for the web
• .NET is a platform that runs on the
operating system

.NET
• Sits on top on the OS (currently all the Windows;
Linux/Unix subset also available – Mono Project)
– About 20MB download
• Provides language interoperability across
platforms
• Strong emphasis on Web connectivity, using XML
web services to connect and share data between
smart client devices, servers, and developers/users
• Platform/language independent

History
• Development began in 1998
• Beta 1 released Oct, 2000
• Beta 2 released July, 2001
• Finalized in Dec, shipping in Feb 2002
• Vista ships with .NET Framework 3.0
(Runtime)

.NET Overview
• Three main elements:
– The Framework (CLR, FCL, ASP, WinForms)
– The Products (Windows, Visual Studio, Office)
– The Services (My Services)
• Framework Goals
– Improved reliability and integrated security.
– Simplified development and deployment.
– Unified API, multi-language support.
• XML is the .NET “Meta-Language”.
• All MS server products now .NET-enabled.

.NET Framework
Framework Class LibraryFramework Class LibraryFramework Class LibraryFramework Class Library
ADO.NET
Network
XML
Security
Threading
Diagnostics
IO
Etc.
Common Language RuntimeCommon Language RuntimeCommon Language RuntimeCommon Language Runtime
Memory Management Common Type System Lifecycle Monitoring
C# VB.NET C++.NET OtherC# VB.NET C++.NET OtherC# VB.NET C++.NET OtherC# VB.NET C++.NET Other
Operating SystemOperating SystemOperating SystemOperating System
VisualVisual
StudioStudio
.NET.NET
VisualVisual
StudioStudio
.NET.NET
Common Language SpecificationCommon Language SpecificationCommon Language SpecificationCommon Language Specification
Windows FormsWindows FormsWindows FormsWindows FormsASP.NETASP.NETASP.NETASP.NET
Web Services
ASP.NET Application Services
Web Forms ControlsControls Drawing
Windows Application Services

Common Language Runtime
• A runtime provides services to executing
programs
– Standard C library, MFC, VB Runtime, JVM
• CLR provided by .NET manages the execution of
code and provides useful services
– Memory management, type system, etc.
– Services exposed through programming languages
• C# exposes more features of the CLR than other languages
(e.g. VB.NET

.NET Framework Class Library
• Framework – you can call it and it can call
you
• Large class library
– Over 2500 classes
– Major components
• Base Class: Networking, security, I/O, files, etc.
• Data and XML Classes
• Web Services/UI
• Windows UI

Framework Libraries
• Web Services
– Expose application functionalities across the Internet, in the same
way as a class expose services to other classes.
– Each Web service can function as an independent entity, and can
cooperate with one another.
– Data described by XML.
• ASP.NET
– Replacement for the Active Server Technology.
– Web Forms provide an easy way to write interactive Web
applications, much in the same way as “normal” Windows
applications.

Framework Libraries
• Provides facilities to generate Windows
GUI-based client applications easily
• Form-oriented
• Standard GUI components
– buttons, textboxes, menus, scrollbars, etc.
• Event-handling

Common Language Specification
• CLS is a set of rules that specifies features that all
languages should support
– Goal: have the .NET framework support multiple
languages
– CLS is an agreement among language designers and
class library designers about the features and usage
conventions that can be relied upon
• Example: public names should not rely on case for uniqueness
since some languages are not case sensitive
• This does not mean all languages are not case sensitive above
the CLR!

Some .NET Languages
• C#
• COBOL
• Eiffel
• Fortran
• Mercury
• Pascal
• Python
• SML
Perl
Smalltalk
VB.NET
VC++.NET
J#.NET
Scheme
….
More are planned or under
development

VB.NET and C#
• VB.NET introduces long sought-after features:
– Inheritance
– Parameterized Class Constructors
– Function Overloading
– Multi-Threading
– Structured Error Handling
– Creating NT Services
• VB.NET not backward compatible with VB6.
• C#
– New modern, object-oriented language
– Similar to C++/Java
– Considered the most powerful language of .NET

.NET: Language-Independent,
(Mostly) Platform- Specific
Person.vb
Address.cs
Company.cbl
CLRPerson
MSIL
Company
MSILAddress
MSIL
WindowsWindows
WindowsWindows
Others?Others?
CLR
CLR
CLR
Deploy
(Visual Basic)
(C#)
(Cobol)

.NET
• .NET built into Windows; running an executable
invokes the CLR automatically instead of
explicitly invoking the JVM
• Being newer, .NET added improvements such as
native XML support, new features to CLR
• About 3 million C++ developers, 3-8 million VB
developers, around 1 million C# developers
• Today, most development and deployment is
Windows

Common Language Runtime
• The CLR is at the core of the .NET platform - the
execution engine
• The CLR provides a “Managed Execution Environment”.
Manages the execution of code and provides services that
make development easier (like the JVM)
• Code that relies on COM and the Win32 API is “Un-
Managed Code” (e.g. built with Visual Studio 6.0, VB6)
• Code developed for a compiler that targets this platform is
referred to as “Managed Code” (e.g. code developed in
VB.NET … C# allows Managed and Unmanaged)

Multiple Languages
• Common Type System makes interoperability
seamless between languages
• Class in one language can inherit from a class in
another language
• Exceptions can be thrown across languages
• Makes it easier to learn a new .NET language
since the same tools and classes are in place
• Can debug across languages

The Common Type System
• At the core of the Framework is a universal type system called the
.NET Common Type System (CTS).
• Everything is an object - but efficient
– Boxing and Unboxing
• All types fall into two categories - Value types and Reference types.
– Value types contain actual data (cannot be null). Stored on the stack.
Always initialized.
– Three kinds of value types: Primitives, structures, and enumerations.
• Language compilers map keywords to the primitive types. For
example, a C# “int” is mapped to System.Int32.

• Reference types are type-safe object pointers. Allocated in the
“managed heap”
• Four kinds of reference types: Classes, arrays, delegates, and
interfaces.
– When instances of value types go out of scope, they are instantly
destroyed and memory is reclaimed.
– When instances of reference types go out of scope, they are garbage
collected.
• Boxing = converting an instance of a value type to a reference type.
Usually done implicitly through parameter passing or variable
assignments.
• UnBoxing = casting a reference type back into a value type variable.

Primitive TypesPrimitive Types
Int16
Int32
Int64
Single
Double
Decimal
Boolean
Byte
Char
Currency
DateTime
TimeSpan
ObjectObject
ArrayArrayStringString
EnumEnum
ValueTypeValueType ExceptionException DelegateDelegate
Multicast
Delegate
Multicast
Delegate
Class1Class1
Class2Class2
Class3Class3

MSIL and JIT Compilation
• Source code is compiled into MSIL (Microsoft Intermediate
Language). Similar to Java bytecodes - CPU-independent instructions
• MSIL allows for runtime type-safety and security, as well as portable
execution platforms.
• The MSIL architecture results in apps that run in one address space -
thus much less OS overhead.
• Compilers also produce “metadata” or glue that binds the code with
debuggers, browsers, etc.
– Definitions of each type in your code.
– Signatures of each type’s members.
– Members that your code references.
– Other runtime data for the CLR.

MSIL and JIT Compilation
• Metadata in the load file along with the MSIL enables
code to be self-describing - no need for separate type
libraries, IDL, or registry entries.
• When code is executed by the CLR, a JIT compilation step
occurs.
– Code is compiled method-by-method to native machine code as
methods are invoked
– Results in performance slowdown when a program is first
executed, but can be efficient for code that is never executed
– Subsequent invocations reuse compiled code, so no slowdown

Packaging: Modules, Types,
Assemblies, and the Manifest
• A “module” refers to a managed binary, such as an EXE or
DLL.
• Modules contain definitions of managed types, such as
classes, interfaces, structures, and enumerations.
• An assembly can be defined as one or more modules that
make up a unit of functionality. Assemblies also can
“contain” other files that make up an application, such as
bitmaps and resource files.
• An assembly is the the fundamental unit of deployment,
version control, activation scoping, and security
permissions.

• An assembly is a set of boundaries:
– A security boundary - the unit to which
permissions are requested and granted.
– A type boundary - the scope of an assembly
uniquely qualifies the types contained within.
– A reference scope boundary - specifies the
types that are exposed outside the assembly.
– A version boundary - all types in an assembly
are versioned together as a unit.
• Avoid multiple version problem for DLL’s

• An assembly contains a “manifest”, which is a catalog of component
metadata containing:
– Assembly name.
– Version (major, minor, revision, build).
– Assembly file list - all files “contained” in the assembly.
– Type references - mapping the managed types included in the assembly
with the files that contain them.
– Scope - private or shared.
– Referenced assemblies.
• In many cases, an assembly consists of a single EXE or DLL -
containing the module’s MSIL, the component metadata, and the
assembly manifest. In other cases, the assembly may consist of many
DLLs, with the manifest in its own file.
• No MSIL code can ever be executed unless there is a manifest
associated with it.

ILDASM
• Can examine assemblies, assembly code
with the ILDASM tool
• Here is ILDASM run on
VideoUnScramble.exe

MSIL Sample Code
IL_006e: ldloc.s V_4
IL_0070: ldloc.1
IL_0071: ldelema [System.Drawing]System.Drawing.Color
IL_0076: ldloc.0
IL_0077: ldloc.1
IL_0078: ldarg.1
IL_0079: sub
IL_007a: ldloc.2
IL_007b: callvirt instance valuetype [System.Drawing]System.Drawing.Color
[System.Drawing]System.Drawing.Bitmap::GetPixel(int32, int32)
IL_0080: stobj [System.Drawing]System.Drawing.Color
IL_0085: ldloc.1
IL_0086: ldc.i4.1
IL_0087: sub
IL_0088: stloc.1
IL_0089: ldloc.1
IL_008a: ldarg.1
IL_008b: bge.s IL_006e
IL_008d: ldc.i4.0
IL_008e: stloc.1
IL_008f: br.s IL_00aa

Summary
• Next we will study C#
• C# does not exist in isolation but has a close
connection with the .NET framework
• .NET
– CLR a relatively new, Java-like platform, but
multi-language
– SrcMSILJITNative Code
– .NET framework includes many class libraries

Introduction to ,NET Framework

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