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Showing content from https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.conditionalattribute below:

ConditionalAttribute Class (System.Diagnostics) | Microsoft Learn

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

public ref class ConditionalAttribute sealed : Attribute

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

[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=true)]
[System.Serializable]
public sealed class ConditionalAttribute : Attribute

[System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Method, AllowMultiple=true)]
[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public sealed class ConditionalAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Method, AllowMultiple=true)>]
type ConditionalAttribute = class
    inherit Attribute

[<System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=true)>]
[<System.Serializable>]
type ConditionalAttribute = class
    inherit Attribute

[<System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Method, AllowMultiple=true)>]
[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type ConditionalAttribute = class
    inherit Attribute

Public NotInheritable Class ConditionalAttribute
Inherits Attribute

Inheritance

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");
        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
*/

#Const CONDITION1 = True
#Const CONDITION2 = True
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

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
  

  #Const DEBUG=True
  

  To undefine the variable, use the following:

  #undef DEBUG
  

  #Const DEBUG=False
  

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

Note

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 Attributes.

Maps a set of names to a corresponding set of dispatch identifiers.

Retrieves the type information for an object, which can be used to get the type information for an interface.

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

Provides access to properties and methods exposed by an object.

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