ConditionalAttribute Class (System.Diagnostics)

You can apply the ConditionalAttribute attribute to methods and classes. However, its use on classes is valid only for types that are derived from Attribute. ConditionalAttribute either will be ignored or will produce a compiler warning or error message if you apply it to any other type.

Note
In the .NET Framework versions 1.0 and 1.1, the ConditionalAttribute attribute can be applied only to methods.

Applying ConditionalAttribute to a method indicates to compilers that a call to the method should not be compiled into Microsoft intermediate language (MSIL) unless the conditional compilation symbol that is associated with ConditionalAttribute is defined. Applying ConditionalAttribute to an attribute indicates that the attribute should not be emitted to metadata unless the conditional compilation symbol is defined. Any arguments passed to the method or attribute are still type-checked by the compiler.

You can use the following techniques to define conditional compilation symbols:

• Compiler command-line options (for example, /define:DEBUG).

• Environment variables in the operating system shell (for example, set DEBUG=1).

• Pragmas in the source code (for example, #define DEBUG to define the compilation variable and #undef DEBUG to undefine it).

Compilers that comply with the Common Language Specification (CLS) are permitted to ignore ConditionalAttribute. The C#, J#, and Visual Basic compilers support ConditionalAttribute; the C++ and JScript compilers do not support the attribute.

ConditionalAttribute is applied to the methods that are defined in the Debug and Trace classes.

For more information about how to use attributes, see Extending Metadata Using Attributes.

The following code example demonstrates the use of ConditionalAttribute. The example assumes that the condition is defined in the /define compiler option. You can obtain different results by changing the compiler option. You can optionally define the conditions in the sample code instead of identifying them as compiler options.

#Const CONDITION1 = True
#Const CONDITION2 = True
Imports System
Imports System.Diagnostics

Class Test

    Shared Sub Main()
        Console.WriteLine("Calling Method1")
        Method1(3)
        Console.WriteLine("Calling Method2")
        Method2()

        Console.WriteLine("Using the Debug class")
        Debug.Listeners.Add(New ConsoleTraceListener())
        Debug.WriteLine("DEBUG is defined")
    End Sub

    <ConditionalAttribute("CONDITION1")> _
    Shared Sub Method1(x As Integer)
        Console.WriteLine("CONDITION1 is defined")
    End Sub

    <ConditionalAttribute("CONDITION1"), ConditionalAttribute("CONDITION2")> _
    Shared Sub Method2()
        Console.WriteLine("CONDITION1 or CONDITIOIN2 is defined")
    End Sub

End Class


' When compiled as shown, the application (named ConsoleApp) 
' produces the following output.

'Calling Method1
'CONDITION1 is defined
'Calling Method2
'CONDITION1 or CONDITION2 is defined
'Using the Debug class
'DEBUG is defined

#define CONDITION1
#define CONDITION2
using System;
using System.Diagnostics;

class Test
{
    static void Main()
    {               
        Console.WriteLine("Calling Method1");
        Method1(3);
        Console.WriteLine("Calling Method2");
        Method2();

        Console.WriteLine("Using the Debug class");
        Debug.Listeners.Add(new ConsoleTraceListener());
        Debug.WriteLine("DEBUG is defined");
    }

    [Conditional("CONDITION1")]
    public static void Method1(int x)
    {
        Console.WriteLine("CONDITION1 is defined");
    }

    [Conditional("CONDITION1"), Conditional("CONDITION2")]  
    public static void Method2()
    {
        Console.WriteLine("CONDITION1 or CONDITION2 is defined");
    }
}

/*
When compiled as shown, the application (named ConsoleApp) 
produces the following output.

Calling Method1
CONDITION1 is defined
Calling Method2
CONDITION1 or CONDITION2 is defined
Using the Debug class
DEBUG is defined
*/

.NET Framework

.NET Framework Client Profile

Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference