Is there a quicker/better way to get Methods that have attribute applied in C#

Question

I have a marker interface something like this:

[AttributeUsage(AttributeTargets.Method, AllowMultiple=false, Inherited=true)]
public class MyAttribute : Attribute
{
}

And i want to apply it to methods on different classes in different assemblies...

Then I want to Get a MethodInfo for all methods that have this attribute applied. I need to search the whole AppDomain and get a reference to all these methods.

I know we can get all types and then get all methods, but is there a quicker/better way to do this? ... or is this the quickest manner to get the information I need?

(I'm using ASP.NET MVC 1.0, C#, ./NET 3.5)

Thanks heaps!

Answer 1

Ultimately, no - you have to scan them. LINQ makes it fairly pain-free though.

        var qry = from asm in AppDomain.CurrentDomain.GetAssemblies()
                  from type in asm.GetTypes()
                  from method in type.GetMethods()
                  where Attribute.IsDefined(method, typeof(MyAttribute))
                  select method;

Note this only scans loaded assemblies "as is".

Answer 2

I've searched for this a few weeks ago as well. I think there is no easier way.
You might be able to spiffy it up a bit with LINQ.

Answer 3

One thing you should consider is an additional attribute that you can apply to a class/struct, indicating that zero or more methods of that type are marked. That should give you at least an order of magnitude improvement in performance.

If the attribute is user-defined (not built in to the .NET framework), then when you're enumerating the assemblies to get the types, you should skip framework assemblies such as mscorlib and System.

Answer 4

If you really need the performance gain, do as Marc suggested and then cache the results in a file. The next time the application load, if the cached file exists, it can load the appropriate method without parsing every assemblies.

Here is an example of a possible cache file:

<attributeCache>

  <assembly name='Assembly1' filename='Assembly1.dll' timestamp='02/02/2010'>
    <type name='Assembly1.Type1'>
      <method name='Method1'/>
    </type>
  </assembly>

 <assembly name='Assembly2' filename='Assembly2.dll' timestamp='02/02/2010' />
</attributeCache>