Switch Class

Provides an abstract base class to create new debugging and tracing switches.

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

'Declaration
Public MustInherit Class Switch
'Usage
Dim instance As Switch

A switch provides an efficient mechanism for controlling tracing and debugging output at run time using external settings. The Switch class implements default behavior for switches, allowing you to change the switch level at run time.

This class is the base class for the BooleanSwitch, SourceSwitch and the TraceSwitch classes. These switches meet most debugging and tracing needs. For more information about trace switches, see Trace Switches.

You must enable tracing or debugging to use a switch. The following syntax is compiler specific. If you use compilers other than C# or Visual Basic, refer to the documentation for your compiler.

  • To enable debugging in C#, add the /d:DEBUG flag to the compiler command line when you compile your code, or you can add #define DEBUG to the top of your file. In Visual Basic, add the /d:DEBUG=True flag to the compiler command line.

  • To enable tracing using in C#, add the /d:TRACE flag to the compiler command line when you compile your code, or add #define TRACE to the top of your file. In Visual Basic, add the /d:TRACE=True flag to the compiler command line.

To set the level of your switch, edit the configuration file that corresponds to the name of your application. Within this file, you can add a switch and set its value, remove a switch, or clear all the switches previously set by the application. The configuration file should be formatted like the following example:

<configuration>
  <system.diagnostics>
    <switches>
      <add name="mySwitch" value="true" />
    </switches>
  </system.diagnostics>
</configuration>

This example configuration section defines a BooleanSwitch with the DisplayName property set to mySwitch and the Enabled value set to true. Within your application, you can use the configured switch value by creating a BooleanSwitch with the same name, as shown in the following code example.

Private Shared boolSwitch As New BooleanSwitch("mySwitch", _
    "Switch in config file")

Public Shared Sub Main(ByVal CmdArgs() As String)
    '...
    Console.WriteLine("Boolean switch {0} configured as {1}", _
        boolSwitch.DisplayName, boolSwitch.Enabled.ToString())
    If boolSwitch.Enabled Then
        '...
    End If

End Sub

Notes to Inheritors:

If you need trace levels, or mechanisms for setting switch levels different from those provided by BooleanSwitch, SourceSwitch and TraceSwitch, you can inherit from Switch. When inheriting from this class, you must implement the SwitchSetting method.

The following example shows how to define a new Switch class with four levels of tracing that can be used to trace a call stack. You can use the switch to instrument your application to log each time the method is entered or exited.

The first example creates the enumeration used to set the level of the switch.

' The following are possible values for the new switch. 
Public Enum MethodTracingSwitchLevel
    Off = 0
    EnteringMethod = 1
    ExitingMethod = 2
    Both = 3
End Enum 'MethodTracingSwitchLevel

The following example creates the new switch. The code implements a Level property to set the value of the new switch. Level calls the protected property SwitchSetting that assigns the value to the new switch. This example also implements two assessor properties to get the assigned value of the switch.

Public Class MyMethodTracingSwitch
    Inherits Switch
    Protected outExit As Boolean 
    Protected outEnter As Boolean 
    Protected myLevel As MethodTracingSwitchLevel

    Public Sub New(displayName As String, description As String)
        MyBase.New(displayName, description)
    End Sub 'New 


    Public Property Level() As MethodTracingSwitchLevel
        Get 
            Return myLevel
        End Get 
        Set
            SetSwitchSetting(CInt(value))
        End Set 
    End Property 


    Protected Sub SetSwitchSetting(value As Integer)
        If value < 0 Then
            value = 0
        End If 
        If value > 3 Then
            value = 3
        End If

        myLevel = CType(value, MethodTracingSwitchLevel)

        outEnter = False 
        If value = CInt(MethodTracingSwitchLevel.EnteringMethod) Or _
            value = CInt(MethodTracingSwitchLevel.Both) Then

            outEnter = True 
        End If

        outExit = False 
        If value = CInt(MethodTracingSwitchLevel.ExitingMethod) Or _
            value = CInt(MethodTracingSwitchLevel.Both) Then

            outExit = True 
        End If 
    End Sub 'SetSwitchSetting


    Public ReadOnly Property OutputExit() As Boolean 
        Get 
            Return outExit
        End Get 
    End Property 


    Public ReadOnly Property OutputEnter() As Boolean 
        Get 
            Return outEnter
        End Get 
    End Property 
End Class 'MyMethodTracingSwitch

The following example creates a new switch in Main. It creates a new switch and assigns it a value. Then, depending on the switch settings, it outputs debugging messages for entering and leaving the method.

Public Class Class1
    ' Create an instance of MyMethodTracingSwitch. 
    Private Shared mySwitch As New _
        MyMethodTracingSwitch("Methods", "Trace entering and exiting method")

    Public Shared Sub Main()
        ' Add the console listener to see trace messages as console output
        Trace.Listeners.Add(New ConsoleTraceListener(True))
        Debug.AutoFlush = True 

        ' Set the switch level to both enter and exit
        mySwitch.Level = MethodTracingSwitchLevel.Both

        ' Write a diagnostic message if the switch is set to entering.
        Debug.WriteLineIf(mySwitch.OutputEnter, "Entering Main")

        ' Insert code to handle processing here... 

        ' Write another diagnostic message if the switch is set to exiting.
        Debug.WriteLineIf(mySwitch.OutputExit, "Exiting Main")
    End Sub 
End Class 'MyClass

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

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
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