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Attributes in C#
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Attributes can be used to encapsulate information about classes, methods etc. There are many predifined attributes like [Obsolete], [Serializable], [NotSerialized] that server different purposes.
We can create our own attributes for using with classes and methods. Name of Attribute classes convensionally ends with the Attribute word.
Definition of Attribute Class
--------------------------------
[AttributeUsage] attribute can be used to specified for what purpose the attribute class is going to be used.
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = true)]
class CodeAttribute : Attribute
{
string name;
string type;
string author;
int mversion, sversion;
DateTime dateWritten;
public CodeAttribute(string Name, string Type)
{
this.name = Name;
this.type = Type;
}
public DateTime DateWritten
{
get { return dateWritten; }
set { dateWritten = value; }
}
public string Name { get { return name; } }
public string Type { get { return type; } }
public string Author
{
get { return author; }
set { author = value; }
}
public int MVersion
{
get { return mversion; }
set { mversion = value; }
}
public int SVersion
{
get { return sversion; }
set { sversion = value; }
}
}
The above code defines a class "CodeAttribute" with some properties and fields.
Using Attributes
----------------
The following code demonstrates how to use the 'CodeAttribute' attribute with classes.
Eventhough the class is named "CodeAttribute" it can be referred to as "Code" (omiting "Attribute").
[Code ("Test","Class",Author="Anil")]
[Code ("Test","Class",Author="Mahesh")]
class Test
{
}
Here the class 'Test' is having a two code attributes with different values.
In the following code the CodeAttribute is applied on a method "MyMethod".
public class Program
{
[Code("MyMethod", "Method", Author = "Anil", MVersion = 1, SVersion = 2)]
public static void MyMethod()
{
}
}
Now let us see how these values can be accessed at runtime.
public static void Main(string[] args)
{
Test tst = new Test();
Type t = tst.GetType();
object[] ar = t.GetCustomAttributes(true);
foreach (Attribute a in ar)
{
if (a is CodeAttribute)
{
CodeAttribute attr = (CodeAttribute)a; //a as CodeAttribute;
Console.WriteLine("Name :{0} Type :{1} Author :{2} Version:{3}.{4}", attr.Name, attr.Type, attr.Author, attr.MVersion, attr.SVersion);
}
}
}
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