What are predefined attributes in C#?

The following are the predefined attributes in C# −

• AttributeUsage
• Conditional
• Obsolete

AttributeUsage

The pre-defined attribute AttributeUsage describes how a custom attribute class can be used. Here is the syntax −

[AttributeUsage (
   validon,
   AllowMultiple = allowmultiple,
   Inherited = inherited
)]

Conditional

This predefined attribute marks a conditional method whose execution depends on a specified preprocessing identifier. It causes conditional compilation of method calls, depending on the specified value such as Debug or Trace.

The following is the syntax −

[Conditional(
   conditionalSymbol
)]

Obsolete

This predefined attribute marks a program entity that should not be used. It enables you to inform the compiler to discard a particular target element. Here is the syntax −

[Obsolete (
   message
)]

[Obsolete (
   message,
   iserror
)]