Importing outside DLLs into .Net platform and using them

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Importing outside DLLs into .Net platform and
using them

• By
• Anupama Atmakur

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Overview

• What is a DLL ?
• Issues in using DLL DLL hell.
• Subtle difference between a DLL and a dot net
  assembly
• What is an assembly?
• How to create a DLL?
• How is a DLL imported into .net?
• Demo showing how to import a DLL into .net?

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What is a DLL?

• DLL stands for dynamic-link library.
• It is an executable file that acts as a shared
  library of functions.
• The executable code for the functions are located
  in a DLL, which are compiled, linked, and stored
  separately from the processes that use them.

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What makes it dynamic?

• DLL is a file that is loaded, and its functions
  linked dynamically at run time.
• It allows an executable module to include only
  the information needed to locate the executable
  code for a DLL.
• Where as in static linking, the linker gets all
  of the referenced functions from the static link
  library and places it with in your code into your
  executable.

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Advantages

• Save memory and disk space.
• Upgrade easier.
• Provide after-market support.
• Provide a mechanism to extend the MFC library
  classes.
• Support Multilanguage programs

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DLL Hell problem using DLLs

• When a DLL is updated on a computer, the older
  version is removed and replaced with the newer
  version. If the new version is not compatible
  with the previous version, this usually crashes
  applications that use the component.

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Solution

• The .NET Framework provides support for
  side-by-side execution, which allows multiple
  versions of an assembly to be installed on the
  same computer, at the same time. As a result
  managed applications can select which version to
  use without affecting other applications that use
  a different version.

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Shift from DLL to Dot Net Assemblies in
Microsoft. NET

• DLL contains library code to be used by any
  program running on Windows.
• Dot net assemblies are understandable to only
  Microsoft. NET and can be used only in .NET
  managed applications.
• Assemblies can maintain versioning with the help
  of the manifest.
• Giving a Strong name to an assembly is a key to
  avoid DLL Hell.

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What is an assembly?

• Assemblies are the building blocks of .NET
  Framework applications.
• They contain the definition of types, versioning
  information for the type, meta-data, and
  manifest.
• They form the fundamental unit of deployment,
  version control, reuse and security permissions.

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How to create a DLL?

• A DLL can be created using the following command
  line statements
• Single-File
• csc /outadd.dll /targetlibrary add.cs
• Multi-File
• csc /outsamlemodule.netmodule /targetmodule
  add.cs
• al /outMultiFileAssembly.dll /targetlibrary
  samlemodule.netmodule

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Using a DLL

• Using command line statement
• csc /targetlibrary /referenceadd.dllprogram.cs
  
• Using GUI

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Strong Name

• Shared assemblies must have a strong name as it
  is a unique identifier of an assembly.
• A strong name consists of the assembly's name,
  version and culture metadata, plus a
  cryptographic public key and a digital signature.
• Public key is used for validation.
• sn -k Keyfile.snk
• This command creates a new pair of keys and
  stores it in a filenamed Keyfile.snk.

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Creating an Assembly Strong Name

• The following attribute are added to the
  AssemblyInfo.cs
• using System.Reflection
• using System.Runtime.CompilerServices
• assembly AssemblyCulture(en-us")
• assembly AssemblyVersion(1.0.0.0")
• assembly AssemblyKeyFile(" Keyfile.snk")

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Sharing an Assembly The Global Assembly Cache

• Install an assembly in the GAC gacutil /i mult.dll
  
• Remove the assembly from the GAC
• gacutil /u math

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• Demo to secure a dll using a keyfile.

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References

• http//msdn2.microsoft.com/en-US/library/3707x96z(
  VS.80).aspx
• http//support.microsoft.com/kb/815065
• http//www.codeproject.com/dll/The_DLL_Hell.asp

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• Questions??