Session 11: In-Depth Explanation

Lecture Topics:

• Creating a Shared Assembly
• Creating Custom Attributes
• Using Reflection to Explore an Assembly
• Using Reflection to Load an Assembly Dynamically
• Files I/O and Streams
  • Working with Drives, Directories, and Files
  • Reading and Writing Files

No Lab

Lecture: Detailed Explanation

1. Creating a Shared Assembly

A shared assembly is a reusable library (typically a .dll) that can be used by multiple applications, often strong-named and deployed to the Global Assembly Cache (GAC) or distributed via NuGet.

• Definition:

  • A shared assembly is a class library project compiled into a .dll, designed for reuse across applications.
  • Example:

    • Create a Class Library (.NET 6) project in Visual Studio 2022:

      // SharedLibrary/EmployeeLibrary.cs
      namespace SharedLibrary
      {
          public class EmployeeLibrary
          {
              public string GenerateEmployeeId() => $"E{Guid.NewGuid().ToString().Substring(0, 4)}";
              public void DisplayEmployee(string name) => Console.WriteLine($"Employee: {name}");
          }
      }
      
      

    • Build to generate SharedLibrary.dll.

    • Using .NET CLI:

      dotnet new classlib -o SharedLibrary
      dotnet build
      
      

• Referencing the Assembly:

  • Add a reference in another project:

    • In Visual Studio: Right-click project → Add → Project Reference → Select SharedLibrary.

    • In .csproj:

      <ItemGroup>
          <ProjectReference Include="..\\\\SharedLibrary\\\\SharedLibrary.csproj" />
      </ItemGroup>
      
      

    • Usage:

      // Program.cs in Console App
      using SharedLibrary;
      
      var lib = new EmployeeLibrary();
      Console.WriteLine(lib.GenerateEmployeeId()); // Outputs: E1234
      lib.DisplayEmployee("Alice"); // Outputs: Employee: Alice
      
      

• Key Points:

  • Shared assemblies are typically strong-named for GAC deployment (see Session 10).

  • In .NET 6, NuGet packages are preferred over GAC for sharing libraries.

  • Create a NuGet package:

    dotnet pack
    dotnet nuget push SharedLibrary.1.0.0.nupkg --source <https://api.nuget.org/v3/index.json>
    
    

• Why This Matters:

  • Shared assemblies promote code reuse and modularity, critical for enterprise applications.

2. Creating Custom Attributes

Custom attributes allow adding metadata to code elements, which can be queried at runtime using reflection.

• Definition:

  • Derive from System.Attribute, typically suffixed with Attribute.

  • Example:

    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
    public class AuditAttribute : Attribute
    {
        public string Description { get; }
        public AuditAttribute(string description) => Description = description;
    }
    
    [Audit("Employee class for HR system")]
    public class Employee
    {
        public string Name { get; set; }
    
        [Audit("Method to display employee details")]
        public void Display() => Console.WriteLine(Name);
    }