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Program.cs
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Program.cs
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using System.Reflection;
using System.Runtime.InteropServices;
using CustomAttributes;
static void ShowPluginInformation(string pluginFolder)
{
var dir = new DirectoryInfo(pluginFolder);
foreach (FileInfo file in dir.GetFiles("*.dll"))
{
Assembly pluginAssembly = Assembly.LoadFrom(file.FullName);
var plugins =
from type in pluginAssembly.ExportedTypes
let info = type.GetCustomAttribute<PluginInformationAttribute>()
where info != null
select new { type, info };
foreach (var plugin in plugins)
{
Console.WriteLine($"Plugin type: {plugin.type.Name}");
Console.WriteLine(
$"Name: {plugin.info.Name}, written by {plugin.info.Author}");
Console.WriteLine($"Description: {plugin.info.Description}");
}
}
}
// We're adding two different sorts of things here, so separate steps
// better express what's happening.
static void ShowPluginInformationMetadataLoadContext(FileInfo file)
{
Type pluginAttributeType = typeof(PluginInformationAttribute);
// Create the list of assembly paths consisting of runtime assemblies and the inspected assembly.
string[] runtimeAssemblies = Directory.GetFiles(RuntimeEnvironment.GetRuntimeDirectory(), "*.dll");
var paths = new List<string>(runtimeAssemblies);
paths.Add(file.FullName);
var resolver = new PathAssemblyResolver(paths);
var mlc = new MetadataLoadContext(resolver);
Assembly pluginAssembly = mlc.LoadFromAssemblyPath(file.FullName);
var plugins =
from type in pluginAssembly.ExportedTypes
let info = type.GetCustomAttributesData().SingleOrDefault(attrData =>
attrData.AttributeType.FullName == pluginAttributeType.FullName)
where info != null
let description = (CustomAttributeNamedArgument?)info.NamedArguments
.SingleOrDefault(a => a.MemberName == "Description")
select new
{
type,
Name = (string)info.ConstructorArguments[0].Value!,
Author = (string)info.ConstructorArguments[1].Value!,
Description = description?.TypedValue.Value
};
foreach (var plugin in plugins)
{
Console.WriteLine($"Plugin type: {plugin.type.Name}");
Console.WriteLine($"Name: {plugin.Name}, written by {plugin.Author}");
Console.WriteLine($"Description: {plugin.Description}");
}
}
Console.WriteLine("Normal reflection");
ShowPluginInformation(Path.GetDirectoryName(typeof(Program).Assembly.Location)!);
Console.WriteLine();
Console.WriteLine("MetadataLoadContext reflection");
ShowPluginInformationMetadataLoadContext(new FileInfo(typeof(Program).Assembly.Location));
// .NET defines this type. The book shows it only for illustration, hence the
// #if false here.
#if false
public interface ICustomAttributeProvider
{
object[] GetCustomAttributes(bool inherit);
object[] GetCustomAttributes(Type attributeType, bool inherit);
bool IsDefined(Type attributeType, bool inherit);
}
#endif