Debug.WriteIf Method (Boolean, Object)


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Writes 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


Type: System.Boolean

The conditional expression to evaluate. If the condition is true, the value is written to the trace listeners in the collection.

Type: System.Object

An object whose name is sent to the Listeners.

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

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:

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

Second example:

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

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

If the switch is set to the TraceLevelError or higher, the example outputs the first name of the value parameter to the Listeners. For information on adding a listener to the Listeners collection, see the TraceListenerCollection class.

Then, if the TraceLevel is set to Verbose, the example outputs a message on the same line as the first message. A line terminator follows the second message.

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

Public Shared Sub MyErrorMethod(myObject As Object)
    ' Write the message if the TraceSwitch level is set to Error or higher.
    Debug.WriteIf(generalSwitch.TraceError, myObject)

    ' Write a second message if the TraceSwitch level is set to Verbose.
    Debug.WriteLineIf(generalSwitch.TraceVerbose, " is not a valid value for this method.")
End Sub 'MyErrorMethod

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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