ConditionalAttribute Class


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Indicates to compilers that a method call or attribute should be ignored unless a specified conditional compilation symbol is defined.

Namespace:   System.Diagnostics
Assembly:  mscorlib (in mscorlib.dll)


[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Method, 
	AllowMultiple = true)]
public sealed class ConditionalAttribute : Attribute


Initializes a new instance of the ConditionalAttribute class.


Gets the conditional compilation symbol that is associated with the ConditionalAttribute attribute.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)


Returns the hash code for this instance.(Inherited from Attribute.)


Gets the Type of the current instance.(Inherited from Object.)


When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

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.

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. You will get a compilation error in Visual Studio if you apply this attribute to a method that does not return void. 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:

  • Use compiler command-line options; for example, /define:DEBUG.

  • Use environment variables in the operating system shell; for example, set DEBUG=1.

  • Use pragmas in the source code; for example, define the compilation variable as follows:

    #define DEBUG

    To undefine the variable, use the following:

    #undef DEBUG

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


In Visual Basic, the AddressOf operator is not affected by this attribute. For example, Call CType(AddressOf delegate, Action) always invokes delegate, although Call delegate() might not.

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

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

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

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

    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
Using the Debug class
DEBUG is defined

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

Any public static ( Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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