C# : Attributes : Part 21

Attributes

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• An attribute tag is used for declaration, which is used to provide basic information about the behaviour of method, classes, structures, etc.
• The declaration of attribute can be done by writting the attribute in square bracket above the element for which you neeed to add
• few Pre defined attributes in .net are as follows
• Obsolete : It is used to make class, method, fields outdated.
• WebMethod : To expose a method as an xml web service method.
• Serializable : Indicates that a class can be serialized. When you are working on cross domain application, e.g. service. if the object will be crossing cross domain boundaries than those classes needs to be serialized.
• Example

 [Obsolete]  
 public static int addNum(int a, int b)  
 {  
   return a + b;  
 }  

• If the above method is called in the programm it will give warning with green underline for it.
• Refer following figure



• When a string message is also specified along with Obsolete, it will give warning from where the method is called along with the typed message
• Refer following figure 



• The above technique is generally used when the developers tries to use old method but is warned to use the new method instead.
• The old method is also to be kept it cannot be removed so as to keep the backward compatibility.
• Thus using attribute Obselete provide the best way to throw warning or message.
• Attribute Obselete can be also used to throw error by writing true along with the message, Refer following image