dotnetframework/System.Composition.AttributedModelv9.0.1
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Provides the foundational attributes that allow you to declare parts for composition, such as imports, exports, and metadata with the Managed Extensibility Framework (MEF).
Get Started
$ dotnet add package System.Composition.AttributedModelReadme
About
System.Composition.AttributedModel is part of the Managed Extensibility Framework (MEF) 2.0, a composition library for .NET that enables dependency injection through attributes or conventions.
This package provides the foundational attributes that allow you to declare parts for composition, such as imports, exports, and metadata. It is used to mark classes, properties, methods, and constructors for MEF's discovery and composition process.
Key Features
- Provides attributes for declaring composable parts, importing dependencies, metadata, and creating shared or non-shared parts
How to Use
Mark classes for export and import using attributes.
using System.Composition;
using System.Composition.Hosting;
var configuration = new ContainerConfiguration()
.WithPart<Service>()
.WithPart<Application>();
using CompositionHost container = configuration.CreateContainer();
Application app = container.GetExport<Application>();
app.Service.Execute();
// Service is running!
[Export]
public class Application
{
[Import]
public Service Service { get; set; }
}
[Export]
public class Service
{
public void Execute() => Console.WriteLine("Service is running!");
}
Metadata can be used to differentiate between multiple exports of the same contract.
using System.Composition;
using System.Composition.Hosting;
ContainerConfiguration configuration = new ContainerConfiguration()
.WithPart<FileLogger>()
.WithPart<ConsoleLogger>()
.WithPart<Application>();
using CompositionHost container = configuration.CreateContainer();
Application app = container.GetExport<Application>();
app.Run();
// Using FileLogger to log.
// FileLogger: Hello, World!
// Using ConsoleLogger to log.
// ConsoleLogger: Hello, World!
public interface ILogger
{
void Log(string message);
}
[Export(typeof(ILogger))]
[ExportMetadata("Name", "FileLogger")]
public class FileLogger : ILogger
{
public void Log(string message) => Console.WriteLine($"FileLogger: {message}");
}
[Export(typeof(ILogger))]
[ExportMetadata("Name", "ConsoleLogger")]
public class ConsoleLogger : ILogger
{
public void Log(string message) => Console.WriteLine($"ConsoleLogger: {message}");
}
[Export]
public class Application
{
[ImportMany]
public required IEnumerable<Lazy<ILogger, IDictionary<string, object>>> Loggers { get; set; }
public void Run()
{
foreach (var logger in Loggers)
{
var name = logger.Metadata["Name"];
Console.WriteLine($"Using {name} to log.");
logger.Value.Log("Hello, World!");
}
}
}