In language, we apply an attribute to a type or member by specifying a
constructor (of that attribute type) and passing appropriate arguments. With
reflection, we can get the attribute instances through
"MemberInfo.GetCustomAttributes()". But this way, we can only get the
instances, not how they are initialized, ie. which constructor is used and
what arguments are passed. This information is written in the metadata and
both Reflector and ILDASM can display it. I am wondering if there is some
.net library method that can get this information, or I'll have to inspect
the raw metadata?

The following example illustrate what I am talking about.

public class MyAttrAttribute: Attribute
{
   int _i;
   string _s;
   public MyAttrAttribute(int i, string s) {}
   public MyAttrAttribute(string s, int i) { _i=i; _s=s;}
}

[MyAttr(3+5, "good"+"bye")]
public class MyClass { }

Reflector display the decompiled MyClass
[MyAttr(8, "goodbye")]
public class MyClass
{
     // Methods
     public MyClass();
}

and ILDASM shows
.class public auto ansi beforefieldinit MyClass
      extends [mscorlib]System.Object
{
 .custom instance void ConApp.MyAttrAttribute::.ctor(int32, string) =
         ( 01 00 08 00 00 00 07 67 6F 6F 64 62 79 65 00 00 ) //
.......goodbye..
} // end of class MyClass