Girish,
As you discovered, the attribute declaration does not cause the constructor
to execute. You would need to call GetCustomAttribute on each member in
order for the constructor of the corresponding attribute to be called.
According to Essential .NET,
"Custom attributes are stored as passive BLOBs in the
CLR metadata. These BLOBs represent serialized
constructor calls to the attribute type... Calling
GetCustomAttributes causes the serialized attribute
constructors to execute as the attribute objects are
instantiated from the metadata prior to your code seeing
them."
Stepping through the attached code illustrates this.
Wally
using System;
using System.Reflection;
class MyAttribute : Attribute
{
static int counter = 0;
public MyAttribute()
{
Console.WriteLine("In constructor of attribute #{0}.",
++MyAttribute.counter);
}
}
[MyAttribute]
class MyClass : Object
{
[MyAttribute]
public int i;
[MyAttribute]
public int j;
}
class MyApp
{
static void Main()
{
Type myType = typeof(MyClass);
MyClass myClass = new MyClass();
MemberInfo[] memberInfos = myType.GetMembers();
foreach(MemberInfo mi in memberInfos)
{
// Custom attribute constructor called
// in the following method
mi.GetCustomAttributes(false);
}
}
}
-----Original Message-----
From: Unmoderated discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Girish Jain
Sent: Tuesday, January 18, 2005 7:19 AM
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: [ADVANCED-DOTNET] When does the attribute contructor gets
executed??
Hi All,
I have written a custom attribute and applied it to the public
fields/properties of a class. This attribute actually maintains certain data
per **Type**.
In the constructor of this attribute class I am adding data to a static
HashTable object, declared in the attribute class (Certainly, after checking
that it does not already exist for the given Type)
For example :
public class A
{
[MyCustom("some data...")]
public int i;
[MyCustom("some data...")]
public string Name
{
get { return this._ColName; }
set { this._ColName = value; }
}
}
I expect the attribute constructor to have already executed by the time I
create the first instance of the class A. But it is not happening.
Can anybody tell me when does the constructor for the attribute gets
executed?
Thanks in advance
Regards,
Girish Jain
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