Trace.WriteIf Method (Boolean, Object, String)


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Writes a category name and the value of the object's ToString method to the trace listeners in the Listeners collection if a condition is true.

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

Public Shared Sub WriteIf (
	condition As Boolean,
	value As Object,
	category As String


Type: System.Boolean

true to cause a message to be written; otherwise, false.

Type: System.Object

An Object whose name is sent to the Listeners.

Type: System.String

A category name used to organize the output.

By default, the output is written to an instance of DefaultTraceListener.

The category parameter can be used to group output messages.

This method calls the Write method of the trace listener.

Notes to Implementers:

You can minimize the performance penalty of instrumenting your application by using If...Then statements instead of using WriteIf statements. The following two code examples send the same debugging message. However, the first example is much faster when tracing is off, because if mySwitch.TraceError evaluates to false you do not call Write. The second example always calls WriteIf, even when mySwitch.TraceError is false and no tracing output is produced. This can result in unnecessary execution of arbitrarily complex code.

First example

    Trace.Write("aNumber = " + aNumber + " out of range");

Second example

Trace.WriteIf(mySwitch.TraceError, "aNumber = " + aNumber + " out of range");

The following example creates a TraceSwitch named generalSwitch. This switch is set outside the code sample.

If the switch is set to the TraceLevelVerbose, the example outputs the name of the myObject and the category to the Listeners. For information on adding a listener to the Listeners collection, see the TraceListenerCollection class.

Then, if the TraceLevel is set to Error or higher, the example outputs the second error message on the same line as the first message. The second message is followed by a line terminator.

' Class-level declaration.
' Create a TraceSwitch.
Private Shared generalSwitch As New TraceSwitch("General", "Entire Application")    

Public Shared Sub MyErrorMethod(myObject As Object, category As String)
    ' Write the message if the TraceSwitch level is set to Verbose.
    Trace.WriteIf(generalSwitch.TraceVerbose, myObject, category)

    ' Write a second message if the TraceSwitch level is set to Error or higher.
    Trace.WriteLineIf(generalSwitch.TraceError, _
        " Object is not valid for this category.")
End Sub

.NET Framework
Available since 1.1
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