Hendry
Just to be clear Cecil can read attributes and you can even extract
out properties and constructor parameters.
The thing u can do with cecil is instantiate and instance of those
attributes at runtime. You would have to switch back to standard
reflection to do that.
So what does this mean for you... Just dont write code in your
attributes and you will be fine. Use Attributes soley for "metadata"
then have another class that does something with that metadata.
For example I have an attribute like this
public class NotifyPropertyAttribute : Attribute
{
public bool PerformEqualityCheck { get; set; }
public string[] AlsoNotifyFor { get; set; }
}
At weaving time I extract the PerformEqualityCheck property using this code
static bool? GetCheckForEquality(CustomAttribute notifyAttribute)
{
var performEqualityCheck =
notifyAttribute.Properties.FirstOrDefault(x => x.Name ==
"PerformEqualityCheck");
var equalityCheckValue = performEqualityCheck.Argument.Value;
if (equalityCheckValue != null)
{
return (bool)equalityCheckValue;
}
return null;
}
Would this approach meet your requirements?
On Sun, Apr 24, 2011 at 12:52 PM, Hendry Luk <[email protected]> wrote:
> Thanks for the response, Jb.
> I was speculating there might be a way to convert (i.e. load) from cecil
> object models into the .net runtime.
> I use cecil because the main business my application does is weaving
> assemblies (AOP), and unfortunately in few places I often need to read
> attribute metadata to control the weaving behavior.
> I guess I will need to use both .net reflection and cecil for this, and
> somehow swap back and forth between them. Efficiency was my concern.
>
> Thanks again
>
> On Sun, Apr 24, 2011 at 5:55 AM, Jb Evain <[email protected]> wrote:
>>
>> Hi,
>>
>> On Sat, Apr 23, 2011 at 9:30 PM, Hendry Luk <[email protected]> wrote:
>> > Hi,
>> > Is there any easy way in cecil to get a certain custom-attributes (of a
>> > specific type) from a method, and execute a virtual method on it?
>> > Just like it can easily be done using a basic System.Reflection.
>> >
>> > The only way i can think of is to manually load the assembly containing
>> > that
>> > attributes (that I've discovered using cecil), then instantiate the
>> > attribute using the constructor-arguments information (from cecil), and
>> > then
>> > copy across all property-values (from cecil). Once you got the attribute
>> > instance, I can then execute the method. It seems to be a lot of work
>> > for
>> > such a _very_ common thing.
>>
>> .net attributes have been designed to be instantiated at runtime.
>> Cecil is not a runtime feature, it just gives you an object model
>> which maps to the serialized metadata. Cecil has obviously no way to
>> instantiate an object based on this metadata.
>>
>> If you want to instantiate attributes, you're looking at the wrong tool.
>>
>> > Oh while I'm here, is there also an easy way to do
>> > type.IsAssignableFrom(type) on cecil? At the moment i'm recursively
>> > checking
>> > all the base-classes within its ancestry line, as well as their
>> > interfaces,
>> > but it feels very inefficient, considering it's also a very common thing
>> > (checking for types assignability is probably far more common than
>> > checking
>> > for an exact equality). Is there a better way to do this?
>>
>> Not really, I don't think I have such a method around.
>>
>> Jb
>>
>> --
>> --
>> mono-cecil
>
> --
> --
> mono-cecil
--
--
mono-cecil
