attributes c#.net software development version 1.0

Attributes

C# .Net Software Development

Version 1.0

Overview

Attributes Provide Declarative Metadata

Must inherit from System.Attribute Conventions TestAttribute class ildasm utility

Copyright 2006-2008 © by Dennis A. Fairclough all rights reserved.

Attributes (C# Standard 1.2/3.0)

Contemporary software design increasingly relies on software components in the form of self-contained and self-describing packages of functionality.

Key to such components is that they present a programming model with properties, methods, and events; They have attributes that provide declarative information

about the component; and they incorporate their own documentation.

Attributes are such and provide declarative metadata


Declarative Information (Attributes)

C# generalizes this capability such that user-defined types of declarative information can be attached to program entities and retrieved at runtime. C# programs specify this additional declarative information by defining and using attributes.


System.Attribute

All attribute classes must derive from the System.Attribute base class provided by the .NET Framework.

If an attribute’s name ends in Attribute, that part of the name can be omitted when the attribute is referenced i.e. TestAttritbute or Test



What are Attributes? Declarative Information Provider (Decorator Pattern) Attributes encapsulate meta information about

assemblies types (classes, structs, enums, etc.) data and method members

Attributes can indicate Threading Model Security Access COM Access style How a type is to be used Serialization style Custom information

Attribute information is stored in the Assembly Manifest

An User-Defined Attribute Class

public class TestAttritbute : Attribute{

}


Example TestAttribute public class TestAttribute : Attribute { private string _Name; public string Name { get { return _Name; } set { _Name = value; } } private string _Mode; public string Mode { get { return _Mode; } set { _Mode = value; } } public TestAttribute(string name) { _Name = name; _Mode = "<none>"; } }//END class TestAttribute


Attribute Usage

[Test("Dennis", Mode="ReadOnly")] class Program { static void Main(string[] args) { MemberInfo member = typeof(Program); TestAttribute mattr = (TestAttribute)Attribute.GetCustomAttribute(member,typeof(TestAttribute) ) as TestAttribute; if (mattr == null) Console.WriteLine("No attribute information"); else Console.WriteLine("TestAttribute for: {0} with {1} and {2}",member,mattr.Name,mattr.Mode); Console.Read(); }//END Main() }//END class Program

Attribute (implied)

Attribute Property


ildasm (MSIL Dissassembler)

ildasm <filename.exe>



FlagsAttribute (Flags)

Used to modify the behavior of an enum Use reflector (or another reflection tool) to

view System.Enum Look at ToString (which has to test for the

FlagsAttribute)

(See Test_Attributes Demo)


Library Attributes CLSCompliantAttribute CategoryAttribute ToolboxBitmapAttribute FlagsAttribute SecurityAttribute WebMethodAttribute And many more.


Attribute Usage Attribute suffix can be omitted

[FlagsAttribute] [Flags]

The attribute tag is actually a constructor call [Flags( )] [PrincipalPermission(SecurityAction.Demand)] Note: You can omit the parens if there are no params

Named constructor parameters: Set Public property values

[PrincipalPermission( SecurityAction.Demand, Name="DEMO/demo", Role="User")]

Property accesses must follow actual parameters


Attribute Usage

Attributes can be used on Assemblies Types Data & Method Members

Attribute usage can be restricted to one type of entity See AttributeTargets enum


Assembly Level Attributes

In the AssemblyInfo.cs file


Querying Attribute Info

Use reflection to access attributes Type.GetCustomAttributes MemberInfo.GetCustomAttributes MethodInfo.GetCustomAttributes MemberInfo.IsDefined etc.


Custom Attribute Must ultimately inherit from System.Attribute Limit where the attribute can be used using the

AttributeUsageAttribute ValidOn (positional parameter)

AttributeTargets enum AllowMultiple (named parameter)

bool (default is false) Inherited (named parameter)

bool (default is true)


The Conditional Attribute

Allows you to define conditional methods Calls to this method are based upon whether

the conditional symbol is defined at the time of the call Parameter(s) are not evaluated if the call is not

made

Similar to #define DEBUG


ObsoleteAttribute

Tag an entity (Class, Struct, Method, etc.) to generate a compile-time warning or error if that entity is used.


Demo

See Attributes Example Code


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attributes c#.net software development version 1.0

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