On Wed, 2009-12-09 at 16:20 +0100, Leszek Ciesielski wrote:
> This foreach loop is a common pattern for loading subclasses/plugins
> from an assembly, is there a better pattern for this?
Yes: assembly-level attributes.
http://weblogs.asp.net/justin_rogers/articles/61042.aspx
See the "1. Assembly Attribute Marking" section.
In short, you'd add a new attribute:
[AttributeUsage(AttributeTargets.Assembly, AllowMultiple=true)]
class PluginAttribute : Attribute {
public PluginAttribute (Type type) {this.Type = type;}
public Type Type {get; private set;}
}
Then specify this attribute at the assembly level:
[assembly:Plugin (typeof(Plugin1))]
[assembly:Plugin (typeof(Plugin2))]
// ...
Then query the assembly for all the PluginAttributes:
Assembly a = ...;
PluginAttribute[] plugins =
(PluginAttribute[]) a.GetCustomAttributes (
typeof(PluginAttribute), true);
foreach (var plugin in plugins)
// plugin.Type is the type to use as a plugin
This can be significantly faster than using Assembly.GetTypes(), as only
the types which are listed in [assembly:Plugin] attributes actually need
to be loaded, which can significantly decrease the amount of memory
consumed (depending on the number of types in the assembly).
- Jon
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